linux/drivers/gpu/drm/drm_dp_i2c_helper.c

/*
 * Copyright © 2009 Keith Packard
 *
 * Permission to use, copy, modify, distribute, and sell this software and its
 * documentation for any purpose is hereby granted without fee, provided that
 * the above copyright notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting documentation, and
 * that the name of the copyright holders not be used in advertising or
 * publicity pertaining to distribution of the software without specific,
 * written prior permission.  The copyright holders make no representations
 * about the suitability of this software for any purpose.  It is provided "as
 * is" without express or implied warranty.
 *
 * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
 * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
 * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
 * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
 * OF THIS SOFTWARE.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/i2c.h>
#include <drm/drm_dp_helper.h>
#include <drm/drmP.h>

/* Run a single AUX_CH I2C transaction, writing/reading data as necessary */
static int
i2c_algo_dp_aux_transaction(struct i2c_adapter *adapter, int mode,
			    uint8_t write_byte, uint8_t *read_byte)
{
	struct i2c_algo_dp_aux_data *algo_data = adapter->algo_data;
	int ret;
	
	ret = (*algo_data->aux_ch)(adapter, mode,
				   write_byte, read_byte);
	return ret;
}

/*
 * I2C over AUX CH
 */

/*
 * Send the address. If the I2C link is running, this 'restarts'
 * the connection with the new address, this is used for doing
 * a write followed by a read (as needed for DDC)
 */
static int
i2c_algo_dp_aux_address(struct i2c_adapter *adapter, u16 address, bool reading)
{
	struct i2c_algo_dp_aux_data *algo_data = adapter->algo_data;
	int mode = MODE_I2C_START;
	int ret;

	if (reading)
		mode |= MODE_I2C_READ;
	else
		mode |= MODE_I2C_WRITE;
	algo_data->address = address;
	algo_data->running = true;
	ret = i2c_algo_dp_aux_transaction(adapter, mode, 0, NULL);
	return ret;
}

/*
 * Stop the I2C transaction. This closes out the link, sending
 * a bare address packet with the MOT bit turned off
 */
static void
i2c_algo_dp_aux_stop(struct i2c_adapter *adapter, bool reading)
{
	struct i2c_algo_dp_aux_data *algo_data = adapter->algo_data;
	int mode = MODE_I2C_STOP;

	if (reading)
		mode |= MODE_I2C_READ;
	else
		mode |= MODE_I2C_WRITE;
	if (algo_data->running) {
		(void) i2c_algo_dp_aux_transaction(adapter, mode, 0, NULL);
		algo_data->running = false;
	}
}

/*
 * Write a single byte to the current I2C address, the
 * the I2C link must be running or this returns -EIO
 */
static int
i2c_algo_dp_aux_put_byte(struct i2c_adapter *adapter, u8 byte)
{
	struct i2c_algo_dp_aux_data *algo_data = adapter->algo_data;
	int ret;

	if (!algo_data->running)
		return -EIO;

	ret = i2c_algo_dp_aux_transaction(adapter, MODE_I2C_WRITE, byte, NULL);
	return ret;
}

/*
 * Read a single byte from the current I2C address, the
 * I2C link must be running or this returns -EIO
 */
static int
i2c_algo_dp_aux_get_byte(struct i2c_adapter *adapter, u8 *byte_ret)
{
	struct i2c_algo_dp_aux_data *algo_data = adapter->algo_data;
	int ret;

	if (!algo_data->running)
		return -EIO;

	ret = i2c_algo_dp_aux_transaction(adapter, MODE_I2C_READ, 0, byte_ret);
	return ret;
}

static int
i2c_algo_dp_aux_xfer(struct i2c_adapter *adapter,
		     struct i2c_msg *msgs,
		     int num)
{
	int ret = 0;
	bool reading = false;
	int m;
	int b;

	for (m = 0; m < num; m++) {
		u16 len = msgs[m].len;
		u8 *buf = msgs[m].buf;
		reading = (msgs[m].flags & I2C_M_RD) != 0;
		ret = i2c_algo_dp_aux_address(adapter, msgs[m].addr, reading);
		if (ret < 0)
			break;
		if (reading) {
			for (b = 0; b < len; b++) {
				ret = i2c_algo_dp_aux_get_byte(adapter, &buf[b]);
				if (ret < 0)
					break;
			}
		} else {
			for (b = 0; b < len; b++) {
				ret = i2c_algo_dp_aux_put_byte(adapter, buf[b]);
				if (ret < 0)
					break;
			}
		}
		if (ret < 0)
			break;
	}
	if (ret >= 0)
		ret = num;
	i2c_algo_dp_aux_stop(adapter, reading);
	DRM_DEBUG_KMS("dp_aux_xfer return %d\n", ret);
	return ret;
}

static u32
i2c_algo_dp_aux_functionality(struct i2c_adapter *adapter)
{
	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL |
	       I2C_FUNC_SMBUS_READ_BLOCK_DATA |
	       I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
	       I2C_FUNC_10BIT_ADDR;
}

static const struct i2c_algorithm i2c_dp_aux_algo = {
	.master_xfer	= i2c_algo_dp_aux_xfer,
	.functionality	= i2c_algo_dp_aux_functionality,
};

static void
i2c_dp_aux_reset_bus(struct i2c_adapter *adapter)
{
	(void) i2c_algo_dp_aux_address(adapter, 0, false);
	(void) i2c_algo_dp_aux_stop(adapter, false);
					   
}

static int
i2c_dp_aux_prepare_bus(struct i2c_adapter *adapter)
{
	adapter->algo = &i2c_dp_aux_algo;
	adapter->retries = 3;
	i2c_dp_aux_reset_bus(adapter);
	return 0;
}

int
i2c_dp_aux_add_bus(struct i2c_adapter *adapter)
{
	int error;
	
	error = i2c_dp_aux_prepare_bus(adapter);
	if (error)
		return error;
	error = i2c_add_adapter(adapter);
	return error;
}
EXPORT_SYMBOL(i2c_dp_aux_add_bus);