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(adap: adapter, msgs, num: 2) == 2)
47 return buf;
48
49 dev_warn(&adapter->dev, "unable to read EDID block.\n");
50 kfree(objp: 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(msecs: 13);
68
69 algo_data->setscl(algo_data->data, 1);
70 if (algo_data->getscl) {
71 for (j = 0; j < 5; j++) {
72 msleep(msecs: 10);
73 if (algo_data->getscl(algo_data->data))
74 break;
75 }
76 if (j == 5)
77 continue;
78 } else {
79 udelay(algo_data->udelay);
80 }
81
82 algo_data->setsda(algo_data->data, 0);
83 msleep(msecs: 15);
84 algo_data->setscl(algo_data->data, 0);
85 msleep(msecs: 15);
86 algo_data->setsda(algo_data->data, 1);
87 msleep(msecs: 15);
88
89 /* Do the real work */
90 edid = fb_do_probe_ddc_edid(adapter);
91 algo_data->setsda(algo_data->data, 0);
92 algo_data->setscl(algo_data->data, 0);
93 msleep(msecs: 15);
94
95 algo_data->setscl(algo_data->data, 1);
96 if (algo_data->getscl) {
97 for (j = 0; j < 10; j++) {
98 msleep(msecs: 10);
99 if (algo_data->getscl(algo_data->data))
100 break;
101 }
102 } else {
103 udelay(algo_data->udelay);
104 }
105
106 algo_data->setsda(algo_data->data, 1);
107 msleep(msecs: 15);
108 algo_data->setscl(algo_data->data, 0);
109 algo_data->setsda(algo_data->data, 0);
110 if (edid)
111 break;
112 }
113 /* Release the DDC lines when done or the Apple Cinema HD display
114 * will switch off
115 */
116 algo_data->setsda(algo_data->data, 1);
117 algo_data->setscl(algo_data->data, 1);
118
119 return edid;
120}
121
122EXPORT_SYMBOL_GPL(fb_ddc_read);
123
124MODULE_AUTHOR("Dennis Munsie <dmunsie@cecropia.com>");
125MODULE_DESCRIPTION("DDC/EDID reading support");
126MODULE_LICENSE("GPL");
127

source code of linux/drivers/video/fbdev/core/fb_ddc.c