drivers/video/fb_ddc.c

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