fb_ddc.c

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/*
 * drivers/video/fb_ddc.c - DDC/EDID read support.
 *
 *  Copyright (C) 2006 Dennis Munsie <[email protected]>
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file COPYING in the main directory of this archive
 * for more details.
 */

#include <linux/delay.h>
#include <linux/device.h>
#include <linux/module.h>
#include <linux/fb.h>
#include <linux/i2c-algo-bit.h>
#include <linux/slab.h>

#include "edid.h"

#define DDC_ADDR    0x50

static unsigned char *fb_do_probe_ddc_edid(struct i2c_adapter *adapter)
{
    unsigned char start = 0x0;
    unsigned char *buf = kmalloc(EDID_LENGTH, GFP_KERNEL);
    struct i2c_msg msgs[] = {
        {
            .addr   = DDC_ADDR,
            .flags  = 0,
            .len    = 1,
            .buf    = &start,
        }, {
            .addr   = DDC_ADDR,
            .flags  = I2C_M_RD,
            .len    = EDID_LENGTH,
            .buf    = buf,
        }
    };

    if (!buf) {
        dev_warn(&adapter->dev, "unable to allocate memory for EDID "
             "block.\n");
        return NULL;
    }

    if (i2c_transfer(adapter, msgs, 2) == 2)
        return buf;

    dev_warn(&adapter->dev, "unable to read EDID block.\n");
    kfree(buf);
    return NULL;
}

unsigned char *fb_ddc_read(struct i2c_adapter *adapter)
{
    struct i2c_algo_bit_data *algo_data = adapter->algo_data;
    unsigned char *edid = NULL;
    int i, j;

    algo_data->setscl(algo_data->data, 1);

    for (i = 0; i < 3; i++) {
        /* For some old monitors we need the
         * following process to initialize/stop DDC
         */
        algo_data->setsda(algo_data->data, 1);
        msleep(13);

        algo_data->setscl(algo_data->data, 1);
        for (j = 0; j < 5; j++) {
            msleep(10);
            if (algo_data->getscl(algo_data->data))
                break;
        }
        if (j == 5)
            continue;

        algo_data->setsda(algo_data->data, 0);
        msleep(15);
        algo_data->setscl(algo_data->data, 0);
        msleep(15);
        algo_data->setsda(algo_data->data, 1);
        msleep(15);

        /* Do the real work */
        edid = fb_do_probe_ddc_edid(adapter);
        algo_data->setsda(algo_data->data, 0);
        algo_data->setscl(algo_data->data, 0);
        msleep(15);

        algo_data->setscl(algo_data->data, 1);
        for (j = 0; j < 10; j++) {
            msleep(10);
            if (algo_data->getscl(algo_data->data))
                break;
        }

        algo_data->setsda(algo_data->data, 1);
        msleep(15);
        algo_data->setscl(algo_data->data, 0);
        algo_data->setsda(algo_data->data, 0);
        if (edid)
            break;
    }
    /* Release the DDC lines when done or the Apple Cinema HD display
     * will switch off
     */
    algo_data->setsda(algo_data->data, 1);
    algo_data->setscl(algo_data->data, 1);

    adapter->class |= I2C_CLASS_DDC;
    return edid;
}

EXPORT_SYMBOL_GPL(fb_ddc_read);

MODULE_AUTHOR("Dennis Munsie <[email protected]>");
MODULE_DESCRIPTION("DDC/EDID reading support");
MODULE_LICENSE("GPL");