2 * driver/vide/fb_ddc.c - DDC/EDID read support.
4 * Copyright (C) 2006 Dennis Munsie <dmunsie@cecropia.com>
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
11 #include <linux/delay.h>
12 #include <linux/device.h>
14 #include <linux/i2c-algo-bit.h>
20 static unsigned char *fb_do_probe_ddc_edid(struct i2c_adapter *adapter)
22 unsigned char start = 0x0;
23 unsigned char *buf = kmalloc(EDID_LENGTH, GFP_KERNEL);
24 struct i2c_msg msgs[] = {
39 dev_warn(&adapter->dev, "unable to allocate memory for EDID "
44 if (i2c_transfer(adapter, msgs, 2) == 2)
47 dev_warn(&adapter->dev, "unable to read EDID block.\n");
52 unsigned char *fb_ddc_read(struct i2c_adapter *adapter)
54 struct i2c_algo_bit_data *algo_data = adapter->algo_data;
55 unsigned char *edid = NULL;
58 algo_data->setscl(algo_data->data, 1);
60 for (i = 0; i < 3; i++) {
61 /* For some old monitors we need the
62 * following process to initialize/stop DDC
64 algo_data->setsda(algo_data->data, 1);
67 algo_data->setscl(algo_data->data, 1);
68 for (j = 0; j < 5; j++) {
70 if (algo_data->getscl(algo_data->data))
76 algo_data->setsda(algo_data->data, 0);
78 algo_data->setscl(algo_data->data, 0);
80 algo_data->setsda(algo_data->data, 1);
83 /* Do the real work */
84 edid = fb_do_probe_ddc_edid(adapter);
85 algo_data->setsda(algo_data->data, 0);
86 algo_data->setscl(algo_data->data, 0);
89 algo_data->setscl(algo_data->data, 1);
90 for (j = 0; j < 10; j++) {
92 if (algo_data->getscl(algo_data->data))
96 algo_data->setsda(algo_data->data, 1);
98 algo_data->setscl(algo_data->data, 0);
99 algo_data->setsda(algo_data->data, 0);
103 /* Release the DDC lines when done or the Apple Cinema HD display
106 algo_data->setsda(algo_data->data, 1);
107 algo_data->setscl(algo_data->data, 1);
109 adapter->class |= I2C_CLASS_DDC;
113 EXPORT_SYMBOL_GPL(fb_ddc_read);
115 MODULE_AUTHOR("Dennis Munsie <dmunsie@cecropia.com>");
116 MODULE_DESCRIPTION("DDC/EDID reading support");
117 MODULE_LICENSE("GPL");