67 lines
2.6 KiB
Plaintext
67 lines
2.6 KiB
Plaintext
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UniPhier System Bus
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The UniPhier System Bus is an external bus that connects on-board devices to
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the UniPhier SoC. It is a simple (semi-)parallel bus with address, data, and
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some control signals. It supports up to 8 banks (chip selects).
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Before any access to the bus, the bus controller must be configured; the bus
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controller registers provide the control for the translation from the offset
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within each bank to the CPU-viewed address. The needed setup includes the base
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address, the size of each bank. Optionally, some timing parameters can be
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optimized for faster bus access.
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Required properties:
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- compatible: should be "socionext,uniphier-system-bus".
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- reg: offset and length of the register set for the bus controller device.
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- #address-cells: should be 2. The first cell is the bank number (chip select).
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The second cell is the address offset within the bank.
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- #size-cells: should be 1.
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- ranges: should provide a proper address translation from the System Bus to
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the parent bus.
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Note:
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The address region(s) that can be assigned for the System Bus is implementation
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defined. Some SoCs can use 0x00000000-0x0fffffff and 0x40000000-0x4fffffff,
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while other SoCs can only use 0x40000000-0x4fffffff. There might be additional
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limitations depending on SoCs and the boot mode. The address translation is
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arbitrary as long as the banks are assigned in the supported address space with
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the required alignment and they do not overlap one another.
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For example, it is possible to map:
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bank 0 to 0x42000000-0x43ffffff, bank 5 to 0x46000000-0x46ffffff
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It is also possible to map:
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bank 0 to 0x48000000-0x49ffffff, bank 5 to 0x44000000-0x44ffffff
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There is no reason to stick to a particular translation mapping, but the
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"ranges" property should provide a "reasonable" default that is known to work.
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The software should initialize the bus controller according to it.
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Example:
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system-bus {
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compatible = "socionext,uniphier-system-bus";
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reg = <0x58c00000 0x400>;
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#address-cells = <2>;
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#size-cells = <1>;
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ranges = <1 0x00000000 0x42000000 0x02000000
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5 0x00000000 0x46000000 0x01000000>;
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ethernet@1,01f00000 {
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compatible = "smsc,lan9115";
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reg = <1 0x01f00000 0x1000>;
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interrupts = <0 48 4>
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phy-mode = "mii";
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};
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uart@5,00200000 {
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compatible = "ns16550a";
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reg = <5 0x00200000 0x20>;
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interrupts = <0 49 4>
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clock-frequency = <12288000>;
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};
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};
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In this example,
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- the Ethernet device is connected at the offset 0x01f00000 of CS1 and
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mapped to 0x43f00000 of the parent bus.
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- the UART device is connected at the offset 0x00200000 of CS5 and
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mapped to 0x46200000 of the parent bus.
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