三星平台的capture设备节点是/dev/fimc0，但是平台可能存在多个摄像头，更特殊的情况是一个video ADC芯片外接多个模拟摄像头，这几天研究了下如何选择capture的摄像头，做个总结。
先对摄像头做个分类，
1. CMM CameraCompact Module 摄像头模组；
2. VIDEO ADC + 模拟摄像头。
视频源的选择是通过VIDIOC_S_INPUT来实现的，这里的视频源既可以是上面第一类的CMM，也可以是第二类的ADC加一个模拟摄像头，video ADC挂几个模拟摄像头就对应几个视频源。
三星FIMC框架为每一个视频源定义了一个结构，以mach-smdkc110.c为例。
1901 static struct s3c_platform_fimc fimc_plat_lsi = {
1902 .srclk_name = "mout_mpll",
1903 .clk_name = "sclk_fimc",
1904 .lclk_name = "sclk_fimc_lclk",
1905 .clk_rate = 166750000,
1906 #if defined(CONFIG_VIDEO_S5K4EA)
1907 .default_cam = CAMERA_CSI_C,
1908 #else
1909 #ifdef CAM_ITU_CH_A
1910 .default_cam = CAMERA_PAR_A,
1911 #else
1912 .default_cam = CAMERA_PAR_B,
1913 #endif
1914 #endif
1915 .camera = {
1916 #ifdef CONFIG_VIDEO_S5K4ECGX
1917 &s5k4ecgx,
1918 #endif
1919 #ifdef CONFIG_VIDEO_S5KA3DFX
1920 &s5ka3dfx,
1921 #endif
1922 #ifdef CONFIG_VIDEO_S5K4BA
1923 &s5k4ba,
1924 #endif
1925 #ifdef CONFIG_VIDEO_S5K4EA
1926 &s5k4ea,
1927 #endif
1928 #ifdef CONFIG_VIDEO_CAM8000
1929 &cam8000,
1930 #endif
1931 #ifdef CONFIG_VIDEO_TW9912
1932 &tw9912_1,
1933 &tw9912_2,
1934 #endif
1935 },
1936 .hw_ver = 0x43,
1937 };
1918 ～ 1938 .camera成员定义了系统可能的视频源，其中s5k4ecgx, s5ka3dfx, s5k4ba, s5k4ea是四个CMM模组， cam8000原生代码的Video ADC，tw9912_1和tw9912_2是我定义的两个camera 视频源，为什么一个TW9912 Video ADC要定义成两个，这是因为在我的项目中TW9912存在两路输入，一个是CVBS另外一个是YPbPr，我认为他们和 TW9912组成了两个camera 视频源。
下面代码演示了如何区分这两个camera通道
1831 static struct s3c_platform_camera tw9912_1 = {
1832 .id = CAMERA_PAR_A,
1833 .type = CAM_TYPE_ITU,
1834 .fmt = ITU_656_YCBCR422_8BIT,
1835 .order422 = CAM_ORDER422_8BIT_CBYCRY,
1836 .i2c_busnum = 1,
1837 .info = &tw9912_1_i2c_info,
1838 .pixelformat = V4L2_PIX_FMT_YUYV,
1839 .srclk_name = "mout_mpll",
1840 .clk_name = "sclk_cam0",
1841 .clk_rate = 44000000,
1842 .line_length = 1440,
1843 .width = 720,
1844 .height = 576,
1845 .window = {
1846 .left = 0,
1847 .top = 0,
1848 .width = 720,
1849 .height = 576,
1850 },
1851
1852 /* Polarity */
1853 .inv_pclk = 0,
1854 .inv_vsync = 0,
1855 .inv_href = 0,
1856 .inv_hsync = 0,
1857
1858 .initialized = 0,
1859 /*
1860 * It is too late to call camera sensor poweron in fimc_camera_init
1861 * so we move power function to board init
1862 */
1863 .cam_power = NULL,
1864 };
1866 static struct s3c_platform_camera tw9912_2 = {
1867 .id = CAMERA_PAR_A,
1868 .type = CAM_TYPE_ITU,
1869 .fmt = ITU_656_YCBCR422_8BIT,
1870 .order422 = CAM_ORDER422_8BIT_CBYCRY,
1871 .i2c_busnum = 1,
1872 .info = &tw9912_2_i2c_info,
1873 .pixelformat = V4L2_PIX_FMT_YUYV,
1874 .srclk_name = "mout_mpll",
1875 .clk_name = "sclk_cam0",
1876 .clk_rate = 44000000,
1877 .line_length = 1440,
1878 .width = 720,
1879 .height = 576,
1880 .window = {
1881 .left = 0,
1882 .top = 0,
1883 .width = 720,
1884 .height = 576,
1885 },
1886
1887 /* Polarity */
1888 .inv_pclk = 0,
1889 .inv_vsync = 0,
1890 .inv_href = 0,
1891 .inv_hsync = 0,
1892
1893 .initialized = 0,
1894 /*
1895 * It is too late to call camera sensor poweron in fimc_camera_init
1896 * so we move power function to board init
1897 */
1898 .cam_power = NULL,
1899 };
他们唯一不同的地方在于.info成员，分别为tw9912_1_i2c_info 和tw9912_2_i2c_info
1796 static struct tw9912_platform_data tw9912_1_plat = {
1797 .default_width = 720,
1798 .default_height = 576,
1799 .pixelformat = V4L2_PIX_FMT_YUYV,
1800 .ifsel = 0,
1801 .ysel = 0,
1802 .csel = 0,
1803 .vsel = 0,
1804 .cam_reset = tw9912_reset,
1805 };
1806
1807 static struct tw9912_platform_data tw9912_2_plat = {
1808 .default_width = 720,
1809 .default_height = 576,
1810 .pixelformat = V4L2_PIX_FMT_YUYV,
1811 .ifsel = 0x20,
1812 .ysel = 0x08,
1813 .csel = 0x2,
1814 .vsel = 0,
1815 .cam_reset = tw9912_reset,
1816 };
1817
1818 static struct i2c_board_info tw9912_1_i2c_info = {
1819 I2C_BOARD_INFO("tw9912", (0x88 >> 1)),
1820 .platform_data = &tw9912_1_plat,
1821 };
1822
1823 static struct i2c_board_info tw9912_2_i2c_info = {
1824 I2C_BOARD_INFO("tw9912", (0x88 >> 1)),
1825 .platform_data = &tw9912_2_plat,
1826 };
i2c_board_info不同的地方是ifsel, ysel, csel, vsel成员，这几个成员对应着tw9912 0x02寄存器（input format）寄存器位
这是tw9912_1和tw9912_2唯一有差别的地方。
当上层调用VIDIOC_S_INPUT时，调用路径如下
fimc_s_input->fimc_configure_subdev->v4l2_i2c_new_subdev_board->v4l2_subdev_call(sd, core, s_config, info->irq, info->platform_data)->
v4l2_subdev_call(sd, core, s_config, info->irq, info->platform_data)调用sd->ops->core->s_config， 这个函数需要在tw9912驱动中实现，info->platform_data就是在mach-smkvc110.c中定义的tw9912_1_i2c_info或者tw9912_2_i2c_info，因此在s_config实现中就可以根据i2c_board_info.platform_data中的ifsel, ysel,
csel, vsel来设置tw9912的输入
总结一下：
1. video ADC芯片驱动要通过s_config来实现视频源的切换
2. 为video ADC的每个输入创建一个s3c_platform_camera 结构，通过i2c_board_info.platform_data来体现输入的差异性
转载自：http://blog.csdn.net/kickxxx/article/details/7789951