940 lines
40 KiB
ReStructuredText
940 lines
40 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+
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.. sectionauthor:: Simon Glass <sjg@chromium.org>
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Design Details
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==============
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This README contains high-level information about driver model, a unified
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way of declaring and accessing drivers in U-Boot. The original work was done
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by:
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* Marek Vasut <marex@denx.de>
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* Pavel Herrmann <morpheus.ibis@gmail.com>
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* Viktor Křivák <viktor.krivak@gmail.com>
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* Tomas Hlavacek <tmshlvck@gmail.com>
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This has been both simplified and extended into the current implementation
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by:
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* Simon Glass <sjg@chromium.org>
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Terminology
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-----------
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Uclass
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a group of devices which operate in the same way. A uclass provides
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a way of accessing individual devices within the group, but always
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using the same interface. For example a GPIO uclass provides
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operations for get/set value. An I2C uclass may have 10 I2C ports,
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4 with one driver, and 6 with another.
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Driver
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some code which talks to a peripheral and presents a higher-level
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interface to it.
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Device
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an instance of a driver, tied to a particular port or peripheral.
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How to try it
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-------------
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Build U-Boot sandbox and run it::
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make sandbox_defconfig
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make
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./u-boot -d u-boot.dtb
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(type 'reset' to exit U-Boot)
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There is a uclass called 'demo'. This uclass handles
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saying hello, and reporting its status. There are two drivers in this
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uclass:
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- simple: Just prints a message for hello, doesn't implement status
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- shape: Prints shapes and reports number of characters printed as status
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The demo class is pretty simple, but not trivial. The intention is that it
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can be used for testing, so it will implement all driver model features and
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provide good code coverage of them. It does have multiple drivers, it
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handles parameter data and platdata (data which tells the driver how
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to operate on a particular platform) and it uses private driver data.
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To try it, see the example session below::
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=>demo hello 1
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Hello '@' from 07981110: red 4
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=>demo status 2
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Status: 0
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=>demo hello 2
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g
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r@
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e@@
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e@@@
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n@@@@
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g@@@@@
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=>demo status 2
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Status: 21
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=>demo hello 4 ^
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y^^^
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e^^^^^
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l^^^^^^^
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l^^^^^^^
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o^^^^^
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w^^^
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=>demo status 4
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Status: 36
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=>
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Running the tests
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-----------------
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The intent with driver model is that the core portion has 100% test coverage
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in sandbox, and every uclass has its own test. As a move towards this, tests
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are provided in test/dm. To run them, try::
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./test/py/test.py --bd sandbox --build -k ut_dm -v
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You should see something like this::
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(venv)$ ./test/py/test.py --bd sandbox --build -k ut_dm -v
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+make O=/root/u-boot/build-sandbox -s sandbox_defconfig
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+make O=/root/u-boot/build-sandbox -s -j8
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============================= test session starts ==============================
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platform linux2 -- Python 2.7.5, pytest-2.9.0, py-1.4.31, pluggy-0.3.1 -- /root/u-boot/venv/bin/python
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cachedir: .cache
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rootdir: /root/u-boot, inifile:
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collected 199 items
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test/py/tests/test_ut.py::test_ut_dm_init PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_adc_bind] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_adc_multi_channel_conversion] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_adc_multi_channel_shot] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_adc_single_channel_conversion] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_adc_single_channel_shot] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_adc_supply] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_adc_wrong_channel_selection] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_autobind] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_autobind_uclass_pdata_alloc] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_autobind_uclass_pdata_valid] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_autoprobe] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_bus_child_post_bind] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_bus_child_post_bind_uclass] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_bus_child_pre_probe_uclass] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_bus_children] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_bus_children_funcs] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_bus_children_iterators] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_bus_parent_data] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_bus_parent_data_uclass] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_bus_parent_ops] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_bus_parent_platdata] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_bus_parent_platdata_uclass] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_children] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_clk_base] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_clk_periph] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_device_get_uclass_id] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_eth] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_eth_act] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_eth_alias] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_eth_prime] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_eth_rotate] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_fdt] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_fdt_offset] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_fdt_pre_reloc] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_fdt_uclass_seq] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_gpio] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_gpio_anon] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_gpio_copy] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_gpio_leak] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_gpio_phandles] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_gpio_requestf] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_i2c_bytewise] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_i2c_find] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_i2c_offset] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_i2c_offset_len] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_i2c_probe_empty] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_i2c_read_write] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_i2c_speed] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_leak] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_led_base] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_led_gpio] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_led_label] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_lifecycle] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_mmc_base] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_net_retry] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_operations] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_ordering] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_pci_base] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_pci_busnum] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_pci_swapcase] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_platdata] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_power_pmic_get] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_power_pmic_io] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_power_regulator_autoset] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_power_regulator_autoset_list] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_power_regulator_get] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_power_regulator_set_get_current] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_power_regulator_set_get_enable] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_power_regulator_set_get_mode] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_power_regulator_set_get_voltage] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_pre_reloc] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_ram_base] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_regmap_base] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_regmap_syscon] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_remoteproc_base] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_remove] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_reset_base] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_reset_walk] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_rtc_base] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_rtc_dual] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_rtc_reset] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_rtc_set_get] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_spi_find] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_spi_flash] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_spi_xfer] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_syscon_base] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_syscon_by_driver_data] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_timer_base] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_uclass] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_uclass_before_ready] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_uclass_devices_find] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_uclass_devices_find_by_name] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_uclass_devices_get] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_uclass_devices_get_by_name] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_usb_base] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_usb_flash] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_usb_keyb] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_usb_multi] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_usb_remove] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_usb_tree] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_usb_tree_remove] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_usb_tree_reorder] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_video_base] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_video_bmp] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_video_bmp_comp] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_video_chars] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_video_context] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_video_rotation1] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_video_rotation2] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_video_rotation3] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_video_text] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_video_truetype] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_video_truetype_bs] PASSED
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test/py/tests/test_ut.py::test_ut[ut_dm_video_truetype_scroll] PASSED
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======================= 84 tests deselected by '-kut_dm' =======================
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================== 115 passed, 84 deselected in 3.77 seconds ===================
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What is going on?
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-----------------
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Let's start at the top. The demo command is in common/cmd_demo.c. It does
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the usual command processing and then:
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.. code-block:: c
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struct udevice *demo_dev;
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ret = uclass_get_device(UCLASS_DEMO, devnum, &demo_dev);
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UCLASS_DEMO means the class of devices which implement 'demo'. Other
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classes might be MMC, or GPIO, hashing or serial. The idea is that the
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devices in the class all share a particular way of working. The class
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presents a unified view of all these devices to U-Boot.
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This function looks up a device for the demo uclass. Given a device
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number we can find the device because all devices have registered with
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the UCLASS_DEMO uclass.
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The device is automatically activated ready for use by uclass_get_device().
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Now that we have the device we can do things like:
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.. code-block:: c
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return demo_hello(demo_dev, ch);
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This function is in the demo uclass. It takes care of calling the 'hello'
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method of the relevant driver. Bearing in mind that there are two drivers,
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this particular device may use one or other of them.
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The code for demo_hello() is in drivers/demo/demo-uclass.c:
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.. code-block:: c
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int demo_hello(struct udevice *dev, int ch)
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{
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const struct demo_ops *ops = device_get_ops(dev);
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if (!ops->hello)
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return -ENOSYS;
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return ops->hello(dev, ch);
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}
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As you can see it just calls the relevant driver method. One of these is
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in drivers/demo/demo-simple.c:
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.. code-block:: c
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static int simple_hello(struct udevice *dev, int ch)
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{
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const struct dm_demo_pdata *pdata = dev_get_platdata(dev);
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printf("Hello from %08x: %s %d\n", map_to_sysmem(dev),
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pdata->colour, pdata->sides);
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return 0;
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}
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So that is a trip from top (command execution) to bottom (driver action)
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but it leaves a lot of topics to address.
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Declaring Drivers
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-----------------
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A driver declaration looks something like this (see
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drivers/demo/demo-shape.c):
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.. code-block:: c
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static const struct demo_ops shape_ops = {
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.hello = shape_hello,
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.status = shape_status,
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};
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U_BOOT_DRIVER(demo_shape_drv) = {
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.name = "demo_shape_drv",
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.id = UCLASS_DEMO,
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.ops = &shape_ops,
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.priv_data_size = sizeof(struct shape_data),
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};
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This driver has two methods (hello and status) and requires a bit of
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private data (accessible through dev_get_priv(dev) once the driver has
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been probed). It is a member of UCLASS_DEMO so will register itself
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there.
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In U_BOOT_DRIVER it is also possible to specify special methods for bind
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and unbind, and these are called at appropriate times. For many drivers
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it is hoped that only 'probe' and 'remove' will be needed.
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The U_BOOT_DRIVER macro creates a data structure accessible from C,
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so driver model can find the drivers that are available.
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The methods a device can provide are documented in the device.h header.
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Briefly, they are:
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* bind - make the driver model aware of a device (bind it to its driver)
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* unbind - make the driver model forget the device
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* ofdata_to_platdata - convert device tree data to platdata - see later
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* probe - make a device ready for use
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* remove - remove a device so it cannot be used until probed again
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The sequence to get a device to work is bind, ofdata_to_platdata (if using
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device tree) and probe.
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Platform Data
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-------------
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Note: platform data is the old way of doing things. It is
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basically a C structure which is passed to drivers to tell them about
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platform-specific settings like the address of its registers, bus
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speed, etc. Device tree is now the preferred way of handling this.
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Unless you have a good reason not to use device tree (the main one
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being you need serial support in SPL and don't have enough SRAM for
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the cut-down device tree and libfdt libraries) you should stay away
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from platform data.
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Platform data is like Linux platform data, if you are familiar with that.
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It provides the board-specific information to start up a device.
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Why is this information not just stored in the device driver itself? The
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idea is that the device driver is generic, and can in principle operate on
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any board that has that type of device. For example, with modern
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highly-complex SoCs it is common for the IP to come from an IP vendor, and
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therefore (for example) the MMC controller may be the same on chips from
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different vendors. It makes no sense to write independent drivers for the
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MMC controller on each vendor's SoC, when they are all almost the same.
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Similarly, we may have 6 UARTs in an SoC, all of which are mostly the same,
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but lie at different addresses in the address space.
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Using the UART example, we have a single driver and it is instantiated 6
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times by supplying 6 lots of platform data. Each lot of platform data
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gives the driver name and a pointer to a structure containing information
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about this instance - e.g. the address of the register space. It may be that
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one of the UARTS supports RS-485 operation - this can be added as a flag in
|
|
the platform data, which is set for this one port and clear for the rest.
|
|
|
|
Think of your driver as a generic piece of code which knows how to talk to
|
|
a device, but needs to know where it is, any variant/option information and
|
|
so on. Platform data provides this link between the generic piece of code
|
|
and the specific way it is bound on a particular board.
|
|
|
|
Examples of platform data include:
|
|
|
|
- The base address of the IP block's register space
|
|
- Configuration options, like:
|
|
- the SPI polarity and maximum speed for a SPI controller
|
|
- the I2C speed to use for an I2C device
|
|
- the number of GPIOs available in a GPIO device
|
|
|
|
Where does the platform data come from? It is either held in a structure
|
|
which is compiled into U-Boot, or it can be parsed from the Device Tree
|
|
(see 'Device Tree' below).
|
|
|
|
For an example of how it can be compiled in, see demo-pdata.c which
|
|
sets up a table of driver names and their associated platform data.
|
|
The data can be interpreted by the drivers however they like - it is
|
|
basically a communication scheme between the board-specific code and
|
|
the generic drivers, which are intended to work on any board.
|
|
|
|
Drivers can access their data via dev->info->platdata. Here is
|
|
the declaration for the platform data, which would normally appear
|
|
in the board file.
|
|
|
|
.. code-block:: c
|
|
|
|
static const struct dm_demo_cdata red_square = {
|
|
.colour = "red",
|
|
.sides = 4.
|
|
};
|
|
|
|
static const struct driver_info info[] = {
|
|
{
|
|
.name = "demo_shape_drv",
|
|
.platdata = &red_square,
|
|
},
|
|
};
|
|
|
|
demo1 = driver_bind(root, &info[0]);
|
|
|
|
|
|
Device Tree
|
|
-----------
|
|
|
|
While platdata is useful, a more flexible way of providing device data is
|
|
by using device tree. In U-Boot you should use this where possible. Avoid
|
|
sending patches which make use of the U_BOOT_DEVICE() macro unless strictly
|
|
necessary.
|
|
|
|
With device tree we replace the above code with the following device tree
|
|
fragment:
|
|
|
|
.. code-block:: c
|
|
|
|
red-square {
|
|
compatible = "demo-shape";
|
|
colour = "red";
|
|
sides = <4>;
|
|
};
|
|
|
|
This means that instead of having lots of U_BOOT_DEVICE() declarations in
|
|
the board file, we put these in the device tree. This approach allows a lot
|
|
more generality, since the same board file can support many types of boards
|
|
(e,g. with the same SoC) just by using different device trees. An added
|
|
benefit is that the Linux device tree can be used, thus further simplifying
|
|
the task of board-bring up either for U-Boot or Linux devs (whoever gets to
|
|
the board first!).
|
|
|
|
The easiest way to make this work it to add a few members to the driver:
|
|
|
|
.. code-block:: c
|
|
|
|
.platdata_auto_alloc_size = sizeof(struct dm_test_pdata),
|
|
.ofdata_to_platdata = testfdt_ofdata_to_platdata,
|
|
|
|
The 'auto_alloc' feature allowed space for the platdata to be allocated
|
|
and zeroed before the driver's ofdata_to_platdata() method is called. The
|
|
ofdata_to_platdata() method, which the driver write supplies, should parse
|
|
the device tree node for this device and place it in dev->platdata. Thus
|
|
when the probe method is called later (to set up the device ready for use)
|
|
the platform data will be present.
|
|
|
|
Note that both methods are optional. If you provide an ofdata_to_platdata
|
|
method then it will be called first (during activation). If you provide a
|
|
probe method it will be called next. See Driver Lifecycle below for more
|
|
details.
|
|
|
|
If you don't want to have the platdata automatically allocated then you
|
|
can leave out platdata_auto_alloc_size. In this case you can use malloc
|
|
in your ofdata_to_platdata (or probe) method to allocate the required memory,
|
|
and you should free it in the remove method.
|
|
|
|
The driver model tree is intended to mirror that of the device tree. The
|
|
root driver is at device tree offset 0 (the root node, '/'), and its
|
|
children are the children of the root node.
|
|
|
|
In order for a device tree to be valid, the content must be correct with
|
|
respect to either device tree specification
|
|
(https://www.devicetree.org/specifications/) or the device tree bindings that
|
|
are found in the doc/device-tree-bindings directory. When not U-Boot specific
|
|
the bindings in this directory tend to come from the Linux Kernel. As such
|
|
certain design decisions may have been made already for us in terms of how
|
|
specific devices are described and bound. In most circumstances we wish to
|
|
retain compatibility without additional changes being made to the device tree
|
|
source files.
|
|
|
|
Declaring Uclasses
|
|
------------------
|
|
|
|
The demo uclass is declared like this:
|
|
|
|
.. code-block:: c
|
|
|
|
U_BOOT_CLASS(demo) = {
|
|
.id = UCLASS_DEMO,
|
|
};
|
|
|
|
It is also possible to specify special methods for probe, etc. The uclass
|
|
numbering comes from include/dm/uclass.h. To add a new uclass, add to the
|
|
end of the enum there, then declare your uclass as above.
|
|
|
|
|
|
Device Sequence Numbers
|
|
-----------------------
|
|
|
|
U-Boot numbers devices from 0 in many situations, such as in the command
|
|
line for I2C and SPI buses, and the device names for serial ports (serial0,
|
|
serial1, ...). Driver model supports this numbering and permits devices
|
|
to be locating by their 'sequence'. This numbering uniquely identifies a
|
|
device in its uclass, so no two devices within a particular uclass can have
|
|
the same sequence number.
|
|
|
|
Sequence numbers start from 0 but gaps are permitted. For example, a board
|
|
may have I2C buses 1, 4, 5 but no 0, 2 or 3. The choice of how devices are
|
|
numbered is up to a particular board, and may be set by the SoC in some
|
|
cases. While it might be tempting to automatically renumber the devices
|
|
where there are gaps in the sequence, this can lead to confusion and is
|
|
not the way that U-Boot works.
|
|
|
|
Each device can request a sequence number. If none is required then the
|
|
device will be automatically allocated the next available sequence number.
|
|
|
|
To specify the sequence number in the device tree an alias is typically
|
|
used. Make sure that the uclass has the DM_UC_FLAG_SEQ_ALIAS flag set.
|
|
|
|
.. code-block:: none
|
|
|
|
aliases {
|
|
serial2 = "/serial@22230000";
|
|
};
|
|
|
|
This indicates that in the uclass called "serial", the named node
|
|
("/serial@22230000") will be given sequence number 2. Any command or driver
|
|
which requests serial device 2 will obtain this device.
|
|
|
|
More commonly you can use node references, which expand to the full path:
|
|
|
|
.. code-block:: none
|
|
|
|
aliases {
|
|
serial2 = &serial_2;
|
|
};
|
|
...
|
|
serial_2: serial@22230000 {
|
|
...
|
|
};
|
|
|
|
The alias resolves to the same string in this case, but this version is
|
|
easier to read.
|
|
|
|
Device sequence numbers are resolved when a device is probed. Before then
|
|
the sequence number is only a request which may or may not be honoured,
|
|
depending on what other devices have been probed. However the numbering is
|
|
entirely under the control of the board author so a conflict is generally
|
|
an error.
|
|
|
|
|
|
Bus Drivers
|
|
-----------
|
|
|
|
A common use of driver model is to implement a bus, a device which provides
|
|
access to other devices. Example of buses include SPI and I2C. Typically
|
|
the bus provides some sort of transport or translation that makes it
|
|
possible to talk to the devices on the bus.
|
|
|
|
Driver model provides some useful features to help with implementing buses.
|
|
Firstly, a bus can request that its children store some 'parent data' which
|
|
can be used to keep track of child state. Secondly, the bus can define
|
|
methods which are called when a child is probed or removed. This is similar
|
|
to the methods the uclass driver provides. Thirdly, per-child platform data
|
|
can be provided to specify things like the child's address on the bus. This
|
|
persists across child probe()/remove() cycles.
|
|
|
|
For consistency and ease of implementation, the bus uclass can specify the
|
|
per-child platform data, so that it can be the same for all children of buses
|
|
in that uclass. There are also uclass methods which can be called when
|
|
children are bound and probed.
|
|
|
|
Here an explanation of how a bus fits with a uclass may be useful. Consider
|
|
a USB bus with several devices attached to it, each from a different (made
|
|
up) uclass::
|
|
|
|
xhci_usb (UCLASS_USB)
|
|
eth (UCLASS_ETHERNET)
|
|
camera (UCLASS_CAMERA)
|
|
flash (UCLASS_FLASH_STORAGE)
|
|
|
|
Each of the devices is connected to a different address on the USB bus.
|
|
The bus device wants to store this address and some other information such
|
|
as the bus speed for each device.
|
|
|
|
To achieve this, the bus device can use dev->parent_platdata in each of its
|
|
three children. This can be auto-allocated if the bus driver (or bus uclass)
|
|
has a non-zero value for per_child_platdata_auto_alloc_size. If not, then
|
|
the bus device or uclass can allocate the space itself before the child
|
|
device is probed.
|
|
|
|
Also the bus driver can define the child_pre_probe() and child_post_remove()
|
|
methods to allow it to do some processing before the child is activated or
|
|
after it is deactivated.
|
|
|
|
Similarly the bus uclass can define the child_post_bind() method to obtain
|
|
the per-child platform data from the device tree and set it up for the child.
|
|
The bus uclass can also provide a child_pre_probe() method. Very often it is
|
|
the bus uclass that controls these features, since it avoids each driver
|
|
having to do the same processing. Of course the driver can still tweak and
|
|
override these activities.
|
|
|
|
Note that the information that controls this behaviour is in the bus's
|
|
driver, not the child's. In fact it is possible that child has no knowledge
|
|
that it is connected to a bus. The same child device may even be used on two
|
|
different bus types. As an example. the 'flash' device shown above may also
|
|
be connected on a SATA bus or standalone with no bus::
|
|
|
|
xhci_usb (UCLASS_USB)
|
|
flash (UCLASS_FLASH_STORAGE) - parent data/methods defined by USB bus
|
|
|
|
sata (UCLASS_SATA)
|
|
flash (UCLASS_FLASH_STORAGE) - parent data/methods defined by SATA bus
|
|
|
|
flash (UCLASS_FLASH_STORAGE) - no parent data/methods (not on a bus)
|
|
|
|
Above you can see that the driver for xhci_usb/sata controls the child's
|
|
bus methods. In the third example the device is not on a bus, and therefore
|
|
will not have these methods at all. Consider the case where the flash
|
|
device defines child methods. These would be used for *its* children, and
|
|
would be quite separate from the methods defined by the driver for the bus
|
|
that the flash device is connetced to. The act of attaching a device to a
|
|
parent device which is a bus, causes the device to start behaving like a
|
|
bus device, regardless of its own views on the matter.
|
|
|
|
The uclass for the device can also contain data private to that uclass.
|
|
But note that each device on the bus may be a memeber of a different
|
|
uclass, and this data has nothing to do with the child data for each child
|
|
on the bus. It is the bus' uclass that controls the child with respect to
|
|
the bus.
|
|
|
|
|
|
Driver Lifecycle
|
|
----------------
|
|
|
|
Here are the stages that a device goes through in driver model. Note that all
|
|
methods mentioned here are optional - e.g. if there is no probe() method for
|
|
a device then it will not be called. A simple device may have very few
|
|
methods actually defined.
|
|
|
|
Bind stage
|
|
^^^^^^^^^^
|
|
|
|
U-Boot discovers devices using one of these two methods:
|
|
|
|
- Scan the U_BOOT_DEVICE() definitions. U-Boot looks up the name specified
|
|
by each, to find the appropriate U_BOOT_DRIVER() definition. In this case,
|
|
there is no path by which driver_data may be provided, but the U_BOOT_DEVICE()
|
|
may provide platdata.
|
|
|
|
- Scan through the device tree definitions. U-Boot looks at top-level
|
|
nodes in the the device tree. It looks at the compatible string in each node
|
|
and uses the of_match table of the U_BOOT_DRIVER() structure to find the
|
|
right driver for each node. In this case, the of_match table may provide a
|
|
driver_data value, but platdata cannot be provided until later.
|
|
|
|
For each device that is discovered, U-Boot then calls device_bind() to create a
|
|
new device, initializes various core fields of the device object such as name,
|
|
uclass & driver, initializes any optional fields of the device object that are
|
|
applicable such as of_offset, driver_data & platdata, and finally calls the
|
|
driver's bind() method if one is defined.
|
|
|
|
At this point all the devices are known, and bound to their drivers. There
|
|
is a 'struct udevice' allocated for all devices. However, nothing has been
|
|
activated (except for the root device). Each bound device that was created
|
|
from a U_BOOT_DEVICE() declaration will hold the platdata pointer specified
|
|
in that declaration. For a bound device created from the device tree,
|
|
platdata will be NULL, but of_offset will be the offset of the device tree
|
|
node that caused the device to be created. The uclass is set correctly for
|
|
the device.
|
|
|
|
The device's bind() method is permitted to perform simple actions, but
|
|
should not scan the device tree node, not initialise hardware, nor set up
|
|
structures or allocate memory. All of these tasks should be left for
|
|
the probe() method.
|
|
|
|
Note that compared to Linux, U-Boot's driver model has a separate step of
|
|
probe/remove which is independent of bind/unbind. This is partly because in
|
|
U-Boot it may be expensive to probe devices and we don't want to do it until
|
|
they are needed, or perhaps until after relocation.
|
|
|
|
Activation/probe
|
|
^^^^^^^^^^^^^^^^
|
|
|
|
When a device needs to be used, U-Boot activates it, by following these
|
|
steps (see device_probe()):
|
|
|
|
1. If priv_auto_alloc_size is non-zero, then the device-private space
|
|
is allocated for the device and zeroed. It will be accessible as
|
|
dev->priv. The driver can put anything it likes in there, but should use
|
|
it for run-time information, not platform data (which should be static
|
|
and known before the device is probed).
|
|
|
|
2. If platdata_auto_alloc_size is non-zero, then the platform data space
|
|
is allocated. This is only useful for device tree operation, since
|
|
otherwise you would have to specific the platform data in the
|
|
U_BOOT_DEVICE() declaration. The space is allocated for the device and
|
|
zeroed. It will be accessible as dev->platdata.
|
|
|
|
3. If the device's uclass specifies a non-zero per_device_auto_alloc_size,
|
|
then this space is allocated and zeroed also. It is allocated for and
|
|
stored in the device, but it is uclass data. owned by the uclass driver.
|
|
It is possible for the device to access it.
|
|
|
|
4. If the device's immediate parent specifies a per_child_auto_alloc_size
|
|
then this space is allocated. This is intended for use by the parent
|
|
device to keep track of things related to the child. For example a USB
|
|
flash stick attached to a USB host controller would likely use this
|
|
space. The controller can hold information about the USB state of each
|
|
of its children.
|
|
|
|
5. All parent devices are probed. It is not possible to activate a device
|
|
unless its predecessors (all the way up to the root device) are activated.
|
|
This means (for example) that an I2C driver will require that its bus
|
|
be activated.
|
|
|
|
6. The device's sequence number is assigned, either the requested one
|
|
(assuming no conflicts) or the next available one if there is a conflict
|
|
or nothing particular is requested.
|
|
|
|
7. If the driver provides an ofdata_to_platdata() method, then this is
|
|
called to convert the device tree data into platform data. This should
|
|
do various calls like fdtdec_get_int(gd->fdt_blob, dev_of_offset(dev), ...)
|
|
to access the node and store the resulting information into dev->platdata.
|
|
After this point, the device works the same way whether it was bound
|
|
using a device tree node or U_BOOT_DEVICE() structure. In either case,
|
|
the platform data is now stored in the platdata structure. Typically you
|
|
will use the platdata_auto_alloc_size feature to specify the size of the
|
|
platform data structure, and U-Boot will automatically allocate and zero
|
|
it for you before entry to ofdata_to_platdata(). But if not, you can
|
|
allocate it yourself in ofdata_to_platdata(). Note that it is preferable
|
|
to do all the device tree decoding in ofdata_to_platdata() rather than
|
|
in probe(). (Apart from the ugliness of mixing configuration and run-time
|
|
data, one day it is possible that U-Boot will cache platform data for
|
|
devices which are regularly de/activated).
|
|
|
|
8. The device's probe() method is called. This should do anything that
|
|
is required by the device to get it going. This could include checking
|
|
that the hardware is actually present, setting up clocks for the
|
|
hardware and setting up hardware registers to initial values. The code
|
|
in probe() can access:
|
|
|
|
- platform data in dev->platdata (for configuration)
|
|
- private data in dev->priv (for run-time state)
|
|
- uclass data in dev->uclass_priv (for things the uclass stores
|
|
about this device)
|
|
|
|
Note: If you don't use priv_auto_alloc_size then you will need to
|
|
allocate the priv space here yourself. The same applies also to
|
|
platdata_auto_alloc_size. Remember to free them in the remove() method.
|
|
|
|
9. The device is marked 'activated'
|
|
|
|
10. The uclass's post_probe() method is called, if one exists. This may
|
|
cause the uclass to do some housekeeping to record the device as
|
|
activated and 'known' by the uclass.
|
|
|
|
Running stage
|
|
^^^^^^^^^^^^^
|
|
|
|
The device is now activated and can be used. From now until it is removed
|
|
all of the above structures are accessible. The device appears in the
|
|
uclass's list of devices (so if the device is in UCLASS_GPIO it will appear
|
|
as a device in the GPIO uclass). This is the 'running' state of the device.
|
|
|
|
Removal stage
|
|
^^^^^^^^^^^^^
|
|
|
|
When the device is no-longer required, you can call device_remove() to
|
|
remove it. This performs the probe steps in reverse:
|
|
|
|
1. The uclass's pre_remove() method is called, if one exists. This may
|
|
cause the uclass to do some housekeeping to record the device as
|
|
deactivated and no-longer 'known' by the uclass.
|
|
|
|
2. All the device's children are removed. It is not permitted to have
|
|
an active child device with a non-active parent. This means that
|
|
device_remove() is called for all the children recursively at this point.
|
|
|
|
3. The device's remove() method is called. At this stage nothing has been
|
|
deallocated so platform data, private data and the uclass data will all
|
|
still be present. This is where the hardware can be shut down. It is
|
|
intended that the device be completely inactive at this point, For U-Boot
|
|
to be sure that no hardware is running, it should be enough to remove
|
|
all devices.
|
|
|
|
4. The device memory is freed (platform data, private data, uclass data,
|
|
parent data).
|
|
|
|
Note: Because the platform data for a U_BOOT_DEVICE() is defined with a
|
|
static pointer, it is not de-allocated during the remove() method. For
|
|
a device instantiated using the device tree data, the platform data will
|
|
be dynamically allocated, and thus needs to be deallocated during the
|
|
remove() method, either:
|
|
|
|
- if the platdata_auto_alloc_size is non-zero, the deallocation
|
|
happens automatically within the driver model core; or
|
|
|
|
- when platdata_auto_alloc_size is 0, both the allocation (in probe()
|
|
or preferably ofdata_to_platdata()) and the deallocation in remove()
|
|
are the responsibility of the driver author.
|
|
|
|
5. The device sequence number is set to -1, meaning that it no longer
|
|
has an allocated sequence. If the device is later reactivated and that
|
|
sequence number is still free, it may well receive the name sequence
|
|
number again. But from this point, the sequence number previously used
|
|
by this device will no longer exist (think of SPI bus 2 being removed
|
|
and bus 2 is no longer available for use).
|
|
|
|
6. The device is marked inactive. Note that it is still bound, so the
|
|
device structure itself is not freed at this point. Should the device be
|
|
activated again, then the cycle starts again at step 2 above.
|
|
|
|
Unbind stage
|
|
^^^^^^^^^^^^
|
|
|
|
The device is unbound. This is the step that actually destroys the device.
|
|
If a parent has children these will be destroyed first. After this point
|
|
the device does not exist and its memory has be deallocated.
|
|
|
|
|
|
Data Structures
|
|
---------------
|
|
|
|
Driver model uses a doubly-linked list as the basic data structure. Some
|
|
nodes have several lists running through them. Creating a more efficient
|
|
data structure might be worthwhile in some rare cases, once we understand
|
|
what the bottlenecks are.
|
|
|
|
|
|
Changes since v1
|
|
----------------
|
|
|
|
For the record, this implementation uses a very similar approach to the
|
|
original patches, but makes at least the following changes:
|
|
|
|
- Tried to aggressively remove boilerplate, so that for most drivers there
|
|
is little or no 'driver model' code to write.
|
|
- Moved some data from code into data structure - e.g. store a pointer to
|
|
the driver operations structure in the driver, rather than passing it
|
|
to the driver bind function.
|
|
- Rename some structures to make them more similar to Linux (struct udevice
|
|
instead of struct instance, struct platdata, etc.)
|
|
- Change the name 'core' to 'uclass', meaning U-Boot class. It seems that
|
|
this concept relates to a class of drivers (or a subsystem). We shouldn't
|
|
use 'class' since it is a C++ reserved word, so U-Boot class (uclass) seems
|
|
better than 'core'.
|
|
- Remove 'struct driver_instance' and just use a single 'struct udevice'.
|
|
This removes a level of indirection that doesn't seem necessary.
|
|
- Built in device tree support, to avoid the need for platdata
|
|
- Removed the concept of driver relocation, and just make it possible for
|
|
the new driver (created after relocation) to access the old driver data.
|
|
I feel that relocation is a very special case and will only apply to a few
|
|
drivers, many of which can/will just re-init anyway. So the overhead of
|
|
dealing with this might not be worth it.
|
|
- Implemented a GPIO system, trying to keep it simple
|
|
|
|
|
|
Pre-Relocation Support
|
|
----------------------
|
|
|
|
For pre-relocation we simply call the driver model init function. Only
|
|
drivers marked with DM_FLAG_PRE_RELOC or the device tree 'u-boot,dm-pre-reloc'
|
|
property are initialised prior to relocation. This helps to reduce the driver
|
|
model overhead. This flag applies to SPL and TPL as well, if device tree is
|
|
enabled (CONFIG_OF_CONTROL) there.
|
|
|
|
Note when device tree is enabled, the device tree 'u-boot,dm-pre-reloc'
|
|
property can provide better control granularity on which device is bound
|
|
before relocation. While with DM_FLAG_PRE_RELOC flag of the driver all
|
|
devices with the same driver are bound, which requires allocation a large
|
|
amount of memory. When device tree is not used, DM_FLAG_PRE_RELOC is the
|
|
only way for statically declared devices via U_BOOT_DEVICE() to be bound
|
|
prior to relocation.
|
|
|
|
It is possible to limit this to specific relocation steps, by using
|
|
the more specialized 'u-boot,dm-spl' and 'u-boot,dm-tpl' flags
|
|
in the device tree node. For U-Boot proper you can use 'u-boot,dm-pre-proper'
|
|
which means that it will be processed (and a driver bound) in U-Boot proper
|
|
prior to relocation, but will not be available in SPL or TPL.
|
|
|
|
To reduce the size of SPL and TPL, only the nodes with pre-relocation properties
|
|
('u-boot,dm-pre-reloc', 'u-boot,dm-spl' or 'u-boot,dm-tpl') are keept in their
|
|
device trees (see README.SPL for details); the remaining nodes are always bound.
|
|
|
|
Then post relocation we throw that away and re-init driver model again.
|
|
For drivers which require some sort of continuity between pre- and
|
|
post-relocation devices, we can provide access to the pre-relocation
|
|
device pointers, but this is not currently implemented (the root device
|
|
pointer is saved but not made available through the driver model API).
|
|
|
|
|
|
SPL Support
|
|
-----------
|
|
|
|
Driver model can operate in SPL. Its efficient implementation and small code
|
|
size provide for a small overhead which is acceptable for all but the most
|
|
constrained systems.
|
|
|
|
To enable driver model in SPL, define CONFIG_SPL_DM. You might want to
|
|
consider the following option also. See the main README for more details.
|
|
|
|
- CONFIG_SYS_MALLOC_SIMPLE
|
|
- CONFIG_DM_WARN
|
|
- CONFIG_DM_DEVICE_REMOVE
|
|
- CONFIG_DM_STDIO
|
|
|
|
|
|
Enabling Driver Model
|
|
---------------------
|
|
|
|
Driver model is being brought into U-Boot gradually. As each subsystems gets
|
|
support, a uclass is created and a CONFIG to enable use of driver model for
|
|
that subsystem.
|
|
|
|
For example CONFIG_DM_SERIAL enables driver model for serial. With that
|
|
defined, the old serial support is not enabled, and your serial driver must
|
|
conform to driver model. With that undefined, the old serial support is
|
|
enabled and driver model is not available for serial. This means that when
|
|
you convert a driver, you must either convert all its boards, or provide for
|
|
the driver to be compiled both with and without driver model (generally this
|
|
is not very hard).
|
|
|
|
See the main README for full details of the available driver model CONFIG
|
|
options.
|
|
|
|
|
|
Things to punt for later
|
|
------------------------
|
|
|
|
Uclasses are statically numbered at compile time. It would be possible to
|
|
change this to dynamic numbering, but then we would require some sort of
|
|
lookup service, perhaps searching by name. This is slightly less efficient
|
|
so has been left out for now. One small advantage of dynamic numbering might
|
|
be fewer merge conflicts in uclass-id.h.
|