drm_dp_i2c_helper.c

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/*
 * 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);