linux/drivers/video/fb_ddc.c
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   1/*
   2 * drivers/video/fb_ddc.c - DDC/EDID read support.
   3 *
   4 *  Copyright (C) 2006 Dennis Munsie <dmunsie@cecropia.com>
   5 *
   6 * This file is subject to the terms and conditions of the GNU General Public
   7 * License.  See the file COPYING in the main directory of this archive
   8 * for more details.
   9 */
  10
  11#include <linux/delay.h>
  12#include <linux/device.h>
  13#include <linux/module.h>
  14#include <linux/fb.h>
  15#include <linux/i2c-algo-bit.h>
  16#include <linux/slab.h>
  17
  18#include "edid.h"
  19
  20#define DDC_ADDR        0x50
  21
  22static unsigned char *fb_do_probe_ddc_edid(struct i2c_adapter *adapter)
  23{
  24        unsigned char start = 0x0;
  25        unsigned char *buf = kmalloc(EDID_LENGTH, GFP_KERNEL);
  26        struct i2c_msg msgs[] = {
  27                {
  28                        .addr   = DDC_ADDR,
  29                        .flags  = 0,
  30                        .len    = 1,
  31                        .buf    = &start,
  32                }, {
  33                        .addr   = DDC_ADDR,
  34                        .flags  = I2C_M_RD,
  35                        .len    = EDID_LENGTH,
  36                        .buf    = buf,
  37                }
  38        };
  39
  40        if (!buf) {
  41                dev_warn(&adapter->dev, "unable to allocate memory for EDID "
  42                         "block.\n");
  43                return NULL;
  44        }
  45
  46        if (i2c_transfer(adapter, msgs, 2) == 2)
  47                return buf;
  48
  49        dev_warn(&adapter->dev, "unable to read EDID block.\n");
  50        kfree(buf);
  51        return NULL;
  52}
  53
  54unsigned char *fb_ddc_read(struct i2c_adapter *adapter)
  55{
  56        struct i2c_algo_bit_data *algo_data = adapter->algo_data;
  57        unsigned char *edid = NULL;
  58        int i, j;
  59
  60        algo_data->setscl(algo_data->data, 1);
  61
  62        for (i = 0; i < 3; i++) {
  63                /* For some old monitors we need the
  64                 * following process to initialize/stop DDC
  65                 */
  66                algo_data->setsda(algo_data->data, 1);
  67                msleep(13);
  68
  69                algo_data->setscl(algo_data->data, 1);
  70                for (j = 0; j < 5; j++) {
  71                        msleep(10);
  72                        if (algo_data->getscl(algo_data->data))
  73                                break;
  74                }
  75                if (j == 5)
  76                        continue;
  77
  78                algo_data->setsda(algo_data->data, 0);
  79                msleep(15);
  80                algo_data->setscl(algo_data->data, 0);
  81                msleep(15);
  82                algo_data->setsda(algo_data->data, 1);
  83                msleep(15);
  84
  85                /* Do the real work */
  86                edid = fb_do_probe_ddc_edid(adapter);
  87                algo_data->setsda(algo_data->data, 0);
  88                algo_data->setscl(algo_data->data, 0);
  89                msleep(15);
  90
  91                algo_data->setscl(algo_data->data, 1);
  92                for (j = 0; j < 10; j++) {
  93                        msleep(10);
  94                        if (algo_data->getscl(algo_data->data))
  95                                break;
  96                }
  97
  98                algo_data->setsda(algo_data->data, 1);
  99                msleep(15);
 100                algo_data->setscl(algo_data->data, 0);
 101                algo_data->setsda(algo_data->data, 0);
 102                if (edid)
 103                        break;
 104        }
 105        /* Release the DDC lines when done or the Apple Cinema HD display
 106         * will switch off
 107         */
 108        algo_data->setsda(algo_data->data, 1);
 109        algo_data->setscl(algo_data->data, 1);
 110
 111        adapter->class |= I2C_CLASS_DDC;
 112        return edid;
 113}
 114
 115EXPORT_SYMBOL_GPL(fb_ddc_read);
 116
 117MODULE_AUTHOR("Dennis Munsie <dmunsie@cecropia.com>");
 118MODULE_DESCRIPTION("DDC/EDID reading support");
 119MODULE_LICENSE("GPL");
 120
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