ubuntu-linux-kernel/drivers/media/usb/dvb-usb-v2/mxl111sf-i2c.c

838 lines
18 KiB
C

/*
* mxl111sf-i2c.c - driver for the MaxLinear MXL111SF
*
* Copyright (C) 2010-2014 Michael Krufky <mkrufky@linuxtv.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#include "mxl111sf-i2c.h"
#include "mxl111sf.h"
/* SW-I2C ----------------------------------------------------------------- */
#define SW_I2C_ADDR 0x1a
#define SW_I2C_EN 0x02
#define SW_SCL_OUT 0x04
#define SW_SDA_OUT 0x08
#define SW_SDA_IN 0x04
#define SW_I2C_BUSY_ADDR 0x2f
#define SW_I2C_BUSY 0x02
static int mxl111sf_i2c_bitbang_sendbyte(struct mxl111sf_state *state,
u8 byte)
{
int i, ret;
u8 data = 0;
mxl_i2c("(0x%02x)", byte);
ret = mxl111sf_read_reg(state, SW_I2C_BUSY_ADDR, &data);
if (mxl_fail(ret))
goto fail;
for (i = 0; i < 8; i++) {
data = (byte & (0x80 >> i)) ? SW_SDA_OUT : 0;
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | data);
if (mxl_fail(ret))
goto fail;
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | data | SW_SCL_OUT);
if (mxl_fail(ret))
goto fail;
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | data);
if (mxl_fail(ret))
goto fail;
}
/* last bit was 0 so we need to release SDA */
if (!(byte & 1)) {
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | SW_SDA_OUT);
if (mxl_fail(ret))
goto fail;
}
/* CLK high for ACK readback */
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | SW_SCL_OUT | SW_SDA_OUT);
if (mxl_fail(ret))
goto fail;
ret = mxl111sf_read_reg(state, SW_I2C_BUSY_ADDR, &data);
if (mxl_fail(ret))
goto fail;
/* drop the CLK after getting ACK, SDA will go high right away */
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | SW_SDA_OUT);
if (mxl_fail(ret))
goto fail;
if (data & SW_SDA_IN)
ret = -EIO;
fail:
return ret;
}
static int mxl111sf_i2c_bitbang_recvbyte(struct mxl111sf_state *state,
u8 *pbyte)
{
int i, ret;
u8 byte = 0;
u8 data = 0;
mxl_i2c("()");
*pbyte = 0;
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | SW_SDA_OUT);
if (mxl_fail(ret))
goto fail;
for (i = 0; i < 8; i++) {
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN |
SW_SCL_OUT | SW_SDA_OUT);
if (mxl_fail(ret))
goto fail;
ret = mxl111sf_read_reg(state, SW_I2C_BUSY_ADDR, &data);
if (mxl_fail(ret))
goto fail;
if (data & SW_SDA_IN)
byte |= (0x80 >> i);
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | SW_SDA_OUT);
if (mxl_fail(ret))
goto fail;
}
*pbyte = byte;
fail:
return ret;
}
static int mxl111sf_i2c_start(struct mxl111sf_state *state)
{
int ret;
mxl_i2c("()");
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | SW_SCL_OUT | SW_SDA_OUT);
if (mxl_fail(ret))
goto fail;
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | SW_SCL_OUT);
if (mxl_fail(ret))
goto fail;
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN); /* start */
mxl_fail(ret);
fail:
return ret;
}
static int mxl111sf_i2c_stop(struct mxl111sf_state *state)
{
int ret;
mxl_i2c("()");
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN); /* stop */
if (mxl_fail(ret))
goto fail;
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | SW_SCL_OUT);
if (mxl_fail(ret))
goto fail;
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | SW_SCL_OUT | SW_SDA_OUT);
if (mxl_fail(ret))
goto fail;
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_SCL_OUT | SW_SDA_OUT);
mxl_fail(ret);
fail:
return ret;
}
static int mxl111sf_i2c_ack(struct mxl111sf_state *state)
{
int ret;
u8 b = 0;
mxl_i2c("()");
ret = mxl111sf_read_reg(state, SW_I2C_BUSY_ADDR, &b);
if (mxl_fail(ret))
goto fail;
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN);
if (mxl_fail(ret))
goto fail;
/* pull SDA low */
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | SW_SCL_OUT);
if (mxl_fail(ret))
goto fail;
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | SW_SDA_OUT);
mxl_fail(ret);
fail:
return ret;
}
static int mxl111sf_i2c_nack(struct mxl111sf_state *state)
{
int ret;
mxl_i2c("()");
/* SDA high to signal last byte read from slave */
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | SW_SCL_OUT | SW_SDA_OUT);
if (mxl_fail(ret))
goto fail;
ret = mxl111sf_write_reg(state, SW_I2C_ADDR,
0x10 | SW_I2C_EN | SW_SDA_OUT);
mxl_fail(ret);
fail:
return ret;
}
/* ------------------------------------------------------------------------ */
static int mxl111sf_i2c_sw_xfer_msg(struct mxl111sf_state *state,
struct i2c_msg *msg)
{
int i, ret;
mxl_i2c("()");
if (msg->flags & I2C_M_RD) {
ret = mxl111sf_i2c_start(state);
if (mxl_fail(ret))
goto fail;
ret = mxl111sf_i2c_bitbang_sendbyte(state,
(msg->addr << 1) | 0x01);
if (mxl_fail(ret)) {
mxl111sf_i2c_stop(state);
goto fail;
}
for (i = 0; i < msg->len; i++) {
ret = mxl111sf_i2c_bitbang_recvbyte(state,
&msg->buf[i]);
if (mxl_fail(ret)) {
mxl111sf_i2c_stop(state);
goto fail;
}
if (i < msg->len - 1)
mxl111sf_i2c_ack(state);
}
mxl111sf_i2c_nack(state);
ret = mxl111sf_i2c_stop(state);
if (mxl_fail(ret))
goto fail;
} else {
ret = mxl111sf_i2c_start(state);
if (mxl_fail(ret))
goto fail;
ret = mxl111sf_i2c_bitbang_sendbyte(state,
(msg->addr << 1) & 0xfe);
if (mxl_fail(ret)) {
mxl111sf_i2c_stop(state);
goto fail;
}
for (i = 0; i < msg->len; i++) {
ret = mxl111sf_i2c_bitbang_sendbyte(state,
msg->buf[i]);
if (mxl_fail(ret)) {
mxl111sf_i2c_stop(state);
goto fail;
}
}
/* FIXME: we only want to do this on the last transaction */
mxl111sf_i2c_stop(state);
}
fail:
return ret;
}
/* HW-I2C ----------------------------------------------------------------- */
#define USB_WRITE_I2C_CMD 0x99
#define USB_READ_I2C_CMD 0xdd
#define USB_END_I2C_CMD 0xfe
#define USB_WRITE_I2C_CMD_LEN 26
#define USB_READ_I2C_CMD_LEN 24
#define I2C_MUX_REG 0x30
#define I2C_CONTROL_REG 0x00
#define I2C_SLAVE_ADDR_REG 0x08
#define I2C_DATA_REG 0x0c
#define I2C_INT_STATUS_REG 0x10
static int mxl111sf_i2c_send_data(struct mxl111sf_state *state,
u8 index, u8 *wdata)
{
int ret = mxl111sf_ctrl_msg(state, wdata[0],
&wdata[1], 25, NULL, 0);
mxl_fail(ret);
return ret;
}
static int mxl111sf_i2c_get_data(struct mxl111sf_state *state,
u8 index, u8 *wdata, u8 *rdata)
{
int ret = mxl111sf_ctrl_msg(state, wdata[0],
&wdata[1], 25, rdata, 24);
mxl_fail(ret);
return ret;
}
static u8 mxl111sf_i2c_check_status(struct mxl111sf_state *state)
{
u8 status = 0;
u8 buf[26];
mxl_i2c_adv("()");
buf[0] = USB_READ_I2C_CMD;
buf[1] = 0x00;
buf[2] = I2C_INT_STATUS_REG;
buf[3] = 0x00;
buf[4] = 0x00;
buf[5] = USB_END_I2C_CMD;
mxl111sf_i2c_get_data(state, 0, buf, buf);
if (buf[1] & 0x04)
status = 1;
return status;
}
static u8 mxl111sf_i2c_check_fifo(struct mxl111sf_state *state)
{
u8 status = 0;
u8 buf[26];
mxl_i2c("()");
buf[0] = USB_READ_I2C_CMD;
buf[1] = 0x00;
buf[2] = I2C_MUX_REG;
buf[3] = 0x00;
buf[4] = 0x00;
buf[5] = I2C_INT_STATUS_REG;
buf[6] = 0x00;
buf[7] = 0x00;
buf[8] = USB_END_I2C_CMD;
mxl111sf_i2c_get_data(state, 0, buf, buf);
if (0x08 == (buf[1] & 0x08))
status = 1;
if ((buf[5] & 0x02) == 0x02)
mxl_i2c("(buf[5] & 0x02) == 0x02"); /* FIXME */
return status;
}
static int mxl111sf_i2c_readagain(struct mxl111sf_state *state,
u8 count, u8 *rbuf)
{
u8 i2c_w_data[26];
u8 i2c_r_data[24];
u8 i = 0;
u8 fifo_status = 0;
int status = 0;
mxl_i2c("read %d bytes", count);
while ((fifo_status == 0) && (i++ < 5))
fifo_status = mxl111sf_i2c_check_fifo(state);
i2c_w_data[0] = 0xDD;
i2c_w_data[1] = 0x00;
for (i = 2; i < 26; i++)
i2c_w_data[i] = 0xFE;
for (i = 0; i < count; i++) {
i2c_w_data[2+(i*3)] = 0x0C;
i2c_w_data[3+(i*3)] = 0x00;
i2c_w_data[4+(i*3)] = 0x00;
}
mxl111sf_i2c_get_data(state, 0, i2c_w_data, i2c_r_data);
/* Check for I2C NACK status */
if (mxl111sf_i2c_check_status(state) == 1) {
mxl_i2c("error!");
} else {
for (i = 0; i < count; i++) {
rbuf[i] = i2c_r_data[(i*3)+1];
mxl_i2c("%02x\t %02x",
i2c_r_data[(i*3)+1],
i2c_r_data[(i*3)+2]);
}
status = 1;
}
return status;
}
#define HWI2C400 1
static int mxl111sf_i2c_hw_xfer_msg(struct mxl111sf_state *state,
struct i2c_msg *msg)
{
int i, k, ret = 0;
u16 index = 0;
u8 buf[26];
u8 i2c_r_data[24];
u16 block_len;
u16 left_over_len;
u8 rd_status[8];
u8 ret_status;
u8 readbuff[26];
mxl_i2c("addr: 0x%02x, read buff len: %d, write buff len: %d",
msg->addr, (msg->flags & I2C_M_RD) ? msg->len : 0,
(!(msg->flags & I2C_M_RD)) ? msg->len : 0);
for (index = 0; index < 26; index++)
buf[index] = USB_END_I2C_CMD;
/* command to indicate data payload is destined for I2C interface */
buf[0] = USB_WRITE_I2C_CMD;
buf[1] = 0x00;
/* enable I2C interface */
buf[2] = I2C_MUX_REG;
buf[3] = 0x80;
buf[4] = 0x00;
/* enable I2C interface */
buf[5] = I2C_MUX_REG;
buf[6] = 0x81;
buf[7] = 0x00;
/* set Timeout register on I2C interface */
buf[8] = 0x14;
buf[9] = 0xff;
buf[10] = 0x00;
#if 0
/* enable Interrupts on I2C interface */
buf[8] = 0x24;
buf[9] = 0xF7;
buf[10] = 0x00;
#endif
buf[11] = 0x24;
buf[12] = 0xF7;
buf[13] = 0x00;
ret = mxl111sf_i2c_send_data(state, 0, buf);
/* write data on I2C bus */
if (!(msg->flags & I2C_M_RD) && (msg->len > 0)) {
mxl_i2c("%d\t%02x", msg->len, msg->buf[0]);
/* control register on I2C interface to initialize I2C bus */
buf[2] = I2C_CONTROL_REG;
buf[3] = 0x5E;
buf[4] = (HWI2C400) ? 0x03 : 0x0D;
/* I2C Slave device Address */
buf[5] = I2C_SLAVE_ADDR_REG;
buf[6] = (msg->addr);
buf[7] = 0x00;
buf[8] = USB_END_I2C_CMD;
ret = mxl111sf_i2c_send_data(state, 0, buf);
/* check for slave device status */
if (mxl111sf_i2c_check_status(state) == 1) {
mxl_i2c("NACK writing slave address %02x",
msg->addr);
/* if NACK, stop I2C bus and exit */
buf[2] = I2C_CONTROL_REG;
buf[3] = 0x4E;
buf[4] = (HWI2C400) ? 0x03 : 0x0D;
ret = -EIO;
goto exit;
}
/* I2C interface can do I2C operations in block of 8 bytes of
I2C data. calculation to figure out number of blocks of i2c
data required to program */
block_len = (msg->len / 8);
left_over_len = (msg->len % 8);
mxl_i2c("block_len %d, left_over_len %d",
block_len, left_over_len);
for (index = 0; index < block_len; index++) {
for (i = 0; i < 8; i++) {
/* write data on I2C interface */
buf[2+(i*3)] = I2C_DATA_REG;
buf[3+(i*3)] = msg->buf[(index*8)+i];
buf[4+(i*3)] = 0x00;
}
ret = mxl111sf_i2c_send_data(state, 0, buf);
/* check for I2C NACK status */
if (mxl111sf_i2c_check_status(state) == 1) {
mxl_i2c("NACK writing slave address %02x",
msg->addr);
/* if NACK, stop I2C bus and exit */
buf[2] = I2C_CONTROL_REG;
buf[3] = 0x4E;
buf[4] = (HWI2C400) ? 0x03 : 0x0D;
ret = -EIO;
goto exit;
}
}
if (left_over_len) {
for (k = 0; k < 26; k++)
buf[k] = USB_END_I2C_CMD;
buf[0] = 0x99;
buf[1] = 0x00;
for (i = 0; i < left_over_len; i++) {
buf[2+(i*3)] = I2C_DATA_REG;
buf[3+(i*3)] = msg->buf[(index*8)+i];
mxl_i2c("index = %d %d data %d",
index, i, msg->buf[(index*8)+i]);
buf[4+(i*3)] = 0x00;
}
ret = mxl111sf_i2c_send_data(state, 0, buf);
/* check for I2C NACK status */
if (mxl111sf_i2c_check_status(state) == 1) {
mxl_i2c("NACK writing slave address %02x",
msg->addr);
/* if NACK, stop I2C bus and exit */
buf[2] = I2C_CONTROL_REG;
buf[3] = 0x4E;
buf[4] = (HWI2C400) ? 0x03 : 0x0D;
ret = -EIO;
goto exit;
}
}
/* issue I2C STOP after write */
buf[2] = I2C_CONTROL_REG;
buf[3] = 0x4E;
buf[4] = (HWI2C400) ? 0x03 : 0x0D;
}
/* read data from I2C bus */
if ((msg->flags & I2C_M_RD) && (msg->len > 0)) {
mxl_i2c("read buf len %d", msg->len);
/* command to indicate data payload is
destined for I2C interface */
buf[2] = I2C_CONTROL_REG;
buf[3] = 0xDF;
buf[4] = (HWI2C400) ? 0x03 : 0x0D;
/* I2C xfer length */
buf[5] = 0x14;
buf[6] = (msg->len & 0xFF);
buf[7] = 0;
/* I2C slave device Address */
buf[8] = I2C_SLAVE_ADDR_REG;
buf[9] = msg->addr;
buf[10] = 0x00;
buf[11] = USB_END_I2C_CMD;
ret = mxl111sf_i2c_send_data(state, 0, buf);
/* check for I2C NACK status */
if (mxl111sf_i2c_check_status(state) == 1) {
mxl_i2c("NACK reading slave address %02x",
msg->addr);
/* if NACK, stop I2C bus and exit */
buf[2] = I2C_CONTROL_REG;
buf[3] = 0xC7;
buf[4] = (HWI2C400) ? 0x03 : 0x0D;
ret = -EIO;
goto exit;
}
/* I2C interface can do I2C operations in block of 8 bytes of
I2C data. calculation to figure out number of blocks of
i2c data required to program */
block_len = ((msg->len) / 8);
left_over_len = ((msg->len) % 8);
index = 0;
mxl_i2c("block_len %d, left_over_len %d",
block_len, left_over_len);
/* command to read data from I2C interface */
buf[0] = USB_READ_I2C_CMD;
buf[1] = 0x00;
for (index = 0; index < block_len; index++) {
/* setup I2C read request packet on I2C interface */
for (i = 0; i < 8; i++) {
buf[2+(i*3)] = I2C_DATA_REG;
buf[3+(i*3)] = 0x00;
buf[4+(i*3)] = 0x00;
}
ret = mxl111sf_i2c_get_data(state, 0, buf, i2c_r_data);
/* check for I2C NACK status */
if (mxl111sf_i2c_check_status(state) == 1) {
mxl_i2c("NACK reading slave address %02x",
msg->addr);
/* if NACK, stop I2C bus and exit */
buf[2] = I2C_CONTROL_REG;
buf[3] = 0xC7;
buf[4] = (HWI2C400) ? 0x03 : 0x0D;
ret = -EIO;
goto exit;
}
/* copy data from i2c data payload to read buffer */
for (i = 0; i < 8; i++) {
rd_status[i] = i2c_r_data[(i*3)+2];
if (rd_status[i] == 0x04) {
if (i < 7) {
mxl_i2c("i2c fifo empty! @ %d",
i);
msg->buf[(index*8)+i] =
i2c_r_data[(i*3)+1];
/* read again */
ret_status =
mxl111sf_i2c_readagain(
state, 8-(i+1),
readbuff);
if (ret_status == 1) {
for (k = 0;
k < 8-(i+1);
k++) {
msg->buf[(index*8)+(k+i+1)] =
readbuff[k];
mxl_i2c("read data: %02x\t %02x",
msg->buf[(index*8)+(k+i)],
(index*8)+(k+i));
mxl_i2c("read data: %02x\t %02x",
msg->buf[(index*8)+(k+i+1)],
readbuff[k]);
}
goto stop_copy;
} else {
mxl_i2c("readagain ERROR!");
}
} else {
msg->buf[(index*8)+i] =
i2c_r_data[(i*3)+1];
}
} else {
msg->buf[(index*8)+i] =
i2c_r_data[(i*3)+1];
}
}
stop_copy:
;
}
if (left_over_len) {
for (k = 0; k < 26; k++)
buf[k] = USB_END_I2C_CMD;
buf[0] = 0xDD;
buf[1] = 0x00;
for (i = 0; i < left_over_len; i++) {
buf[2+(i*3)] = I2C_DATA_REG;
buf[3+(i*3)] = 0x00;
buf[4+(i*3)] = 0x00;
}
ret = mxl111sf_i2c_get_data(state, 0, buf,
i2c_r_data);
/* check for I2C NACK status */
if (mxl111sf_i2c_check_status(state) == 1) {
mxl_i2c("NACK reading slave address %02x",
msg->addr);
/* if NACK, stop I2C bus and exit */
buf[2] = I2C_CONTROL_REG;
buf[3] = 0xC7;
buf[4] = (HWI2C400) ? 0x03 : 0x0D;
ret = -EIO;
goto exit;
}
for (i = 0; i < left_over_len; i++) {
msg->buf[(block_len*8)+i] =
i2c_r_data[(i*3)+1];
mxl_i2c("read data: %02x\t %02x",
i2c_r_data[(i*3)+1],
i2c_r_data[(i*3)+2]);
}
}
/* indicate I2C interface to issue NACK
after next I2C read op */
buf[0] = USB_WRITE_I2C_CMD;
buf[1] = 0x00;
/* control register */
buf[2] = I2C_CONTROL_REG;
buf[3] = 0x17;
buf[4] = (HWI2C400) ? 0x03 : 0x0D;
buf[5] = USB_END_I2C_CMD;
ret = mxl111sf_i2c_send_data(state, 0, buf);
/* control register */
buf[2] = I2C_CONTROL_REG;
buf[3] = 0xC7;
buf[4] = (HWI2C400) ? 0x03 : 0x0D;
}
exit:
/* STOP and disable I2C MUX */
buf[0] = USB_WRITE_I2C_CMD;
buf[1] = 0x00;
/* de-initilize I2C BUS */
buf[5] = USB_END_I2C_CMD;
mxl111sf_i2c_send_data(state, 0, buf);
/* Control Register */
buf[2] = I2C_CONTROL_REG;
buf[3] = 0xDF;
buf[4] = 0x03;
/* disable I2C interface */
buf[5] = I2C_MUX_REG;
buf[6] = 0x00;
buf[7] = 0x00;
/* de-initilize I2C BUS */
buf[8] = USB_END_I2C_CMD;
mxl111sf_i2c_send_data(state, 0, buf);
/* disable I2C interface */
buf[2] = I2C_MUX_REG;
buf[3] = 0x81;
buf[4] = 0x00;
/* disable I2C interface */
buf[5] = I2C_MUX_REG;
buf[6] = 0x00;
buf[7] = 0x00;
/* disable I2C interface */
buf[8] = I2C_MUX_REG;
buf[9] = 0x00;
buf[10] = 0x00;
buf[11] = USB_END_I2C_CMD;
mxl111sf_i2c_send_data(state, 0, buf);
return ret;
}
/* ------------------------------------------------------------------------ */
int mxl111sf_i2c_xfer(struct i2c_adapter *adap,
struct i2c_msg msg[], int num)
{
struct dvb_usb_device *d = i2c_get_adapdata(adap);
struct mxl111sf_state *state = d->priv;
int hwi2c = (state->chip_rev > MXL111SF_V6);
int i, ret;
if (mutex_lock_interruptible(&d->i2c_mutex) < 0)
return -EAGAIN;
for (i = 0; i < num; i++) {
ret = (hwi2c) ?
mxl111sf_i2c_hw_xfer_msg(state, &msg[i]) :
mxl111sf_i2c_sw_xfer_msg(state, &msg[i]);
if (mxl_fail(ret)) {
mxl_debug_adv("failed with error %d on i2c transaction %d of %d, %sing %d bytes to/from 0x%02x",
ret, i+1, num,
(msg[i].flags & I2C_M_RD) ?
"read" : "writ",
msg[i].len, msg[i].addr);
break;
}
}
mutex_unlock(&d->i2c_mutex);
return i == num ? num : -EREMOTEIO;
}