/*
 * drivers/video/fb_ddc.c - DDC/EDID read support.
 *
 *  Copyright (C) 2006 Dennis Munsie <dmunsie@cecropia.com>
 *
 * 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/export.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);
                if (algo_data->getscl) {
                        for (j = 0; j < 5; j++) {
                                msleep(10);
                                if (algo_data->getscl(algo_data->data))
                                        break;
                        }
                        if (j == 5)
                                continue;
                } else {
                        udelay(algo_data->udelay);
                }

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

                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);

        return edid;
}

EXPORT_SYMBOL_GPL(fb_ddc_read);

MODULE_AUTHOR("Dennis Munsie <dmunsie@cecropia.com>");
MODULE_DESCRIPTION("DDC/EDID reading support");
MODULE_LICENSE("GPL");