深入学习Linux摄像头（四）三星平台fimc驱动详解

「爱情、让人受尽委屈。」 2021-10-30 02:34 567阅读 0赞

**深入学习Linux摄像头系列**

[深入学习Linux摄像头（一）v4l2应用编程][Linux_v4l2]

[深入学习Linux摄像头（二）v4l2驱动框架][Linux_v4l2 1]

[深入学习Linux摄像头（三）虚拟摄像头驱动分析][Linux]

[深入学习Linux摄像头（四）三星平台fimc驱动详解][Linux_fimc]

# 深入学习Linux摄像头（四）三星平台fimc驱动详解 #

### 文章目录 ###

*  深入学习Linux摄像头（四）三星平台fimc驱动详解
 *   *  一、硬件接口
     *  二、fimc驱动总览
     *  三、源码分析
     *   *  3.1 几个主要对象
         *  3.2 fimc的平台设备
         *  3.2 fimc的平台驱动
         *  3.3 s5k4ba的驱动程序
         *  3.4 fimc驱动详细分析

## 一、硬件接口 ##

*  摄像头
    
    摄像头传感器由摄像头接口和控制接口(一般为i2c)组成
    
    摄像头接口用于传输传感器采集到的数据
    
    控制接口用于控制摄像头传感器(例如设置图像格式…)
    
    ![在这里插入图片描述][20190815163602864.PNG]
 *  芯片
    
    芯片上由多个摄像头控制器，多个摄像头接口，多个i2c控制器(i2c总线)
    
    摄像头控制器负责控制摄像头接口和处理接收到的数据，摄像头接口负责传输图像数据，i2c控制器负责传输控制信息
    
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjQ2MjIwMg_size_16_color_FFFFFF_t_70]

摄像头传感器和芯片的接法如下

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjQ2MjIwMg_size_16_color_FFFFFF_t_70 1]

其中摄像头控制器和摄像头接口是分离的，摄像头控制器可以选择控制哪一个摄像头接口

fimc是三星平台摄像头控制器的一套驱动程序

## 二、fimc驱动总览 ##

fimc的文件集中在`drivers/media/video/samsung/fimc`目录下

有以下文件

*  fimc\_dev.c
    
    fimc的平台驱动
 *  fimc\_v4l2.c
    
    实现了一系列的ioctl操作
 *  fimc\_capture.c
    
    实现了capture功能
 *  fimc\_output.c
    
    实现了output功能
 *  fimc\_overlay.c
    
    实现了overlay功能
 *  fimc\_regs.c
    
    fimc控制器的寄存器操作
 *  csis.c
    
    csis接口的摄像头

各文件的组织形式如下

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjQ2MjIwMg_size_16_color_FFFFFF_t_70 2]

`fimc_dev.c`是平台的驱动，负责一些初始化的工作，`fimc_v4l2.c`设置了一系列的ioctl操作，`fimc_capture.c`、`fimc_output.c`、`fimc_overlay.c`实现了一些具体功能的ioctl，通过`fimc_regs.c`实现对摄像头控制器的硬件操作

## 三、源码分析 ##

### 3.1 几个主要对象 ###

在分析源码前，先介绍几个对象

*  s3c\_platform\_camera
    
    摄像头传感器
    
        struct s3c_platform_camera {
              
            /* 标记摄像头在哪个摄像头接口 */
        	enum fimc_cam_index		id;
        
            /* 摄像头接口类型 */
        	enum fimc_cam_type		type; //ITU or MIPI
            
            /* 像素格式 */
        	enum fimc_cam_format	fmt;
        
            /* i2c相关信息 */
        	int						i2c_busnum; //摄像头所接的i2c总线
        	struct i2c_board_info	  *info; //摄像头的i2c信息
        	struct v4l2_subdev		 *sd; //表明这是一个v4l2_subdev
        
        	int				width; //图像的宽
        	int				height; //图像的高
        
        
        	/* 摄像头接口的时序极性 */
        	int				inv_pclk;
        	int				inv_vsync;
        	int				inv_href;
        	int				inv_hsync;
        
            /* 使能摄像头 */
        	int				(*cam_power)(int onoff);
        };
 *  s3c\_platform\_fimc
    
    摄像头接口的平台信息
    
        struct s3c_platform_fimc {
              
            /* 时钟相关 */
        	const char			srclk_name[16];		/* source of interface clock name */
        	const char			clk_name[16];		/* interface clock name */
        	const char			lclk_name[16];		/* interface clock name */
        	u32				clk_rate;		/* clockrate for interface clock */
        	
            /* 保存摄像头的信息 */
        	struct s3c_platform_camera	*camera[5];		/* FIXME */
        	
        	void				(*cfg_gpio)(struct platform_device *pdev);
        	int				(*clk_on)(struct platform_device *pdev, struct clk *clk);
        	int				(*clk_off)(struct platform_device *pdev, struct clk *clk);
        };
 *  fimc\_control
    
    摄像头控制器
    
        struct fimc_control {
              
            /* 寄存器地址 */
        	void __iomem			*regs;
        
        	/* video_device和v4l2_device */
        	struct video_device		*vd;
        	struct v4l2_device		v4l2_dev;
        
            ...
        };
 *  fimc\_global
    
    fimc驱动的全局变量
    
        struct fimc_global {
              
        	struct fimc_control		ctrl[FIMC_DEVICES]; //摄像头控制器
        	struct s3c_platform_camera	camera[FIMC_MAXCAMS]; //摄像头
        	int				camera_isvalid[FIMC_MAXCAMS]; //标记是否存在摄像头
        	int				active_camera; // 当前使用的摄像头
        };

介绍完上面几个结构体后，开始分析源码

### 3.2 fimc的平台设备 ###

fimc的驱动采用的platform总线，分成设备和驱动，我们先介绍设备

首先看`mach-smdkc110.c`文件，这里描述了一系列的硬件信息

这里有多个摄像头描述，其中一个如下

static struct s3c_platform_camera s5k4ba = {
        
    	.id		= CAMERA_PAR_A, //摄像头在接口A
    	.type		= CAM_TYPE_ITU, //ITU模式
    	.fmt		= ITU_601_YCBCR422_8BIT, //传感器输入格式YCbCr422
    	.order422	= CAM_ORDER422_8BIT_CBYCRY, //输入Y U V的顺序
    	.i2c_busnum	= 0, //i2c总线0
    	.info		= &s5k4ba_i2c_info, //i2c的设备描述
    	.pixelformat	= V4L2_PIX_FMT_UYVY, //经过摄像头控制器后的输出格式
    	.srclk_name	= "mout_mpll",
    	.clk_name	= "sclk_cam1",
    	.clk_rate	= 44000000, //时钟频率
    	.line_length	= 1920,
    	.width		= 800, //图像宽
    	.height		= 600, //图像高
    	/* 裁剪 */
        .window		= {
        
    		.left	= 0,
    		.top	= 0,
    		.width	= 800,
    		.height	= 600,
    	},
    
    	/* 时序极性 */
    	.inv_pclk	= 0,
    	.inv_vsync	= 1,
    	.inv_href	= 0,
    	.inv_hsync	= 0,
    
    	.initialized	= 0,
    	.cam_power	= s5k5ba_power_en,
    };

看一看`s5k4ba_i2c_info`

static struct i2c_board_info  s5k4ba_i2c_info = {
        
    	I2C_BOARD_INFO("S5K4BA", 0x2d),
    	.platform_data = &s5k4ba_plat,
    };

其中表明i2c设备名称为`S5K4BA`，i2c从地址`0x2d`

再看一看`s5k5ba_power_en`如何使能摄像头

static int s5k5ba_power_en(int onoff)
    {
        
        smdkv210_cam1_power(onoff);
    }

/* 设置GPIO */
    static int smdkv210_cam0_power(int onoff)
    {
        
    	int err;
    	/* Camera A */
    	err = gpio_request(GPIO_PS_VOUT, "GPH0");
    	if (err)
    		printk(KERN_ERR "failed to request GPH0 for CAM_2V8\n");
    
    	s3c_gpio_setpull(GPIO_PS_VOUT, S3C_GPIO_PULL_NONE);
    	gpio_direction_output(GPIO_PS_VOUT, 0);
    	gpio_direction_output(GPIO_PS_VOUT, 1);
    	gpio_free(GPIO_PS_VOUT);
    
    	return 0;
    }

`s3c_platform_camera`描述一个摄像头的信息(哪个摄像头接口，在哪个i2c总线，像素格式…)

`s5k4ba`被嵌入到fimc的平台数据中

static struct s3c_platform_fimc fimc_plat_lsi = {
        
    	.srclk_name	= "mout_mpll",
    	.clk_name	= "sclk_fimc",
    	.lclk_name	= "sclk_fimc_lclk",
    	.clk_rate	= 166750000,
    	.default_cam	= CAMERA_PAR_A, //默认接口
        
        /* 保存摄像头信息，可以多个 */
    	.camera		= {
        
    			&s5k4ba,
    	},
    	.hw_ver		= 0x43,
    };

`s3c_platform_fimc`存放着所有摄像头的信息，供驱动程序读取

在`mach-smdkc110.c`文件中，`fimc_plat_lsi`最终被设置到fimc的平台设备的平台数据中

s3c_fimc0_set_platdata(&fimc_plat_lsi);
    s3c_fimc1_set_platdata(&fimc_plat_lsi);
    s3c_fimc2_set_platdata(&fimc_plat_lsi);

void __init s3c_fimc0_set_platdata(struct s3c_platform_fimc *pd)
    {
        
        struct s3c_platform_fimc *npd;
        
        /* 复制一份 */
        npd = kmemdup(pd, sizeof(struct s3c_platform_fimc), GFP_KERNEL);
        
        npd->cfg_gpio = s3c_fimc0_cfg_gpio;
        npd->clk_on = s3c_fimc_clk_on;
        npd->clk_off = s3c_fimc_clk_off;
        
        /* 分配视频缓存 */
        npd->pmem_start = s5p_get_media_memory_bank(S5P_MDEV_FIMC0, 1);
    
        /* 将器设置到fimc平台设备的平台数据中 */
    	s3c_device_fimc0.dev.platform_data = npd;
    }

其中`s3c_device_fimc0`是一个platform总线的平台设备，在内核启动时，会被注册进内核

struct platform_device s3c_device_fimc0 = {
        
    	.name		= "s3c-fimc",
    	.id		= 0,
    	.num_resources	= ARRAY_SIZE(s3c_fimc0_resource),
    	.resource	= s3c_fimc0_resource,
    };

static struct resource s3c_fimc0_resource[] = {
        
    	[0] = {
        
    		.start	= S5P_PA_FIMC0, //寄存器地址
    		.end	= S5P_PA_FIMC0 + S5P_SZ_FIMC0 - 1,
    		.flags	= IORESOURCE_MEM,
    	},
    	[1] = {
        
    		.start	= IRQ_FIMC0, //中断
    		.end	= IRQ_FIMC0,
    		.flags	= IORESOURCE_IRQ,
    	},
    };

对于S5PV210来说，芯片上有三个摄像头控制器，那么就有三个fimc的平台设备，三个控制器在经过驱动程序后会生成/dev/video0、/dev/video1、/dev/video2三个设备节点

上面各对象的包裹关系如下

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjQ2MjIwMg_size_16_color_FFFFFF_t_70 3]

然后再将platform\_device注册进内核

### 3.2 fimc的平台驱动 ###

接下来分析platform\_driver

platform\_driver在fimc\_dev.c中注册

static struct platform_driver fimc_driver = {
        
    	.probe		= fimc_probe,
    	.remove		= fimc_remove,
    	.suspend	= fimc_suspend,
    	.resume		= fimc_resume,
    	.driver		= {
        
    		.name	= FIMC_NAME,
    		.owner	= THIS_MODULE,
    	},
    };
    
    static int fimc_register(void)
    {
        
    	platform_driver_register(&fimc_driver);
    
    	return 0;
    }

当platform\_dev和platform\_driver匹配的时候，会调用probe函数

struct fimc_global *fimc_dev;
    ...
    static int __devinit fimc_probe(struct platform_device *pdev)
    {
        
        struct s3c_platform_fimc *pdata;
        struct fimc_control *ctrl;
        
        /* 为全局变量分配内存 */
        if (!fimc_dev)
            fimc_dev = kzalloc(sizeof(*fimc_dev), GFP_KERNEL);
    
        /* 通过平台设备的信息注册摄像头控制器 */
        ctrl = fimc_register_controller(pdev);
    
        /* 注册v4l2_device，主要是为了管理v4l2_subdev */
    	v4l2_device_register(&pdev->dev, &ctrl->v4l2_dev);
    
        /* 初始化fimc的全局变量 */
    	if (!fimc_dev->initialized)
            fimc_init_global(pdev);
    
        /* 注册video_device字符设备，生成设备节点 */
    	video_register_device(ctrl->vd, VFL_TYPE_GRABBER, ctrl->id);
    }

首先来看一看`fimc_register_controller`

struct fimc_control *fimc_register_controller(struct platform_device *pdev)
    {
        
        struct s3c_platform_fimc *pdata;
    	struct fimc_control *ctrl;
        
        /* 从platform_dev中中获取fimc的平台设备信息 */
        pdata = to_fimc_plat(&pdev->dev);
        
        /* 从全局变量中得到fimc ctrl */
    	ctrl = get_fimc_ctrl(id);
        
        /* 设置ctrl的video_device */
    	ctrl->vd = &fimc_video_device[id];
    
        /* 申请寄存器地址空间 */
    	platform_get_resource(pdev, IORESOURCE_MEM, 0);
        request_mem_region(res->start, res->end - res->start + 1, pdev->name);
        ctrl->regs = ioremap(res->start, res->end - res->start + 1);
        
        /* 申请中断 */
        ctrl->irq = platform_get_irq(pdev, 0);
        request_irq(ctrl->irq, fimc_irq, IRQF_DISABLED, ctrl->name, ctrl)
            
        /* 初始化寄存器，复位摄像头控制器 */
        fimc_hwset_reset(ctrl);
    }

`fimc_video_device`是一个video\_device的全局数组，每一个摄像头控制器对应其中一项

struct video_device fimc_video_device[FIMC_DEVICES] = {
        
    	[0] = {
        
    		.fops = &fimc_fops,
    		.ioctl_ops = &fimc_v4l2_ops,
    		.release = fimc_vdev_release,
    	},
    	[1] = {
        
    		.fops = &fimc_fops,
    		.ioctl_ops = &fimc_v4l2_ops,
    		.release = fimc_vdev_release,
    	},
    	[2] = {
        
    		.fops = &fimc_fops,
    		.ioctl_ops = &fimc_v4l2_ops,
    		.release = fimc_vdev_release,
    	},
    };

static const struct v4l2_file_operations fimc_fops = {
        
    	.owner		= THIS_MODULE,
    	.open		= fimc_open,
    	.release	= fimc_release,
    	.ioctl		= video_ioctl2,
    	.read		= fimc_read,
    	.write		= fimc_write,
    	.mmap		= fimc_mmap,
    	.poll		= fimc_poll,
    };

const struct v4l2_ioctl_ops fimc_v4l2_ops = {
        
    	.vidioc_querycap		= fimc_querycap,
    	.vidioc_reqbufs			= fimc_reqbufs,
    	.vidioc_querybuf		= fimc_querybuf,
    	.vidioc_g_ctrl			= fimc_g_ctrl,
    	.vidioc_s_ctrl			= fimc_s_ctrl,
    	.vidioc_s_ext_ctrls		= fimc_s_ext_ctrls,
    	.vidioc_cropcap			= fimc_cropcap,
    	.vidioc_g_crop			= fimc_g_crop,
    	.vidioc_s_crop			= fimc_s_crop,
    	.vidioc_streamon		= fimc_streamon,
    	.vidioc_streamoff		= fimc_streamoff,
    	.vidioc_qbuf			= fimc_qbuf,
    	.vidioc_dqbuf			= fimc_dqbuf,
    	.vidioc_enum_fmt_vid_cap	= fimc_enum_fmt_vid_capture,
    	.vidioc_g_fmt_vid_cap		= fimc_g_fmt_vid_capture,
    	.vidioc_s_fmt_vid_cap		= fimc_s_fmt_vid_capture,
    	.vidioc_try_fmt_vid_cap		= fimc_try_fmt_vid_capture,
    	.vidioc_enum_input		= fimc_enum_input,
    	.vidioc_g_input			= fimc_g_input,
    	.vidioc_s_input			= fimc_s_input,
    	.vidioc_g_parm			= fimc_g_parm,
    	.vidioc_s_parm			= fimc_s_parm,
    	.vidioc_queryctrl		= fimc_queryctrl,
    	.vidioc_querymenu		= fimc_querymenu,
    	.vidioc_g_fmt_vid_out		= fimc_g_fmt_vid_out,
    	.vidioc_s_fmt_vid_out		= fimc_s_fmt_vid_out,
    	.vidioc_try_fmt_vid_out		= fimc_try_fmt_vid_out,
    	.vidioc_g_fbuf			= fimc_g_fbuf,
    	.vidioc_s_fbuf			= fimc_s_fbuf,
    	.vidioc_try_fmt_vid_overlay	= fimc_try_fmt_overlay,
    	.vidioc_g_fmt_vid_overlay	= fimc_g_fmt_vid_overlay,
    	.vidioc_s_fmt_vid_overlay	= fimc_s_fmt_vid_overlay,
    };

可以看到`fimc_register_controller`中设置了ctrl的video\_device，申请了寄存器的地址空间，申请了中断(中断程序我们后面会分析)，复位摄像头控制器的寄存器

接下来再来看一看`fimc_probe`的`fimc_init_global`函数

static int fimc_init_global(struct platform_device *pdev)
    {
        
        struct s3c_platform_fimc *pdata;
        pdata = to_fimc_plat(&pdev->dev);
        
        for()
        {
        
            cam = pdata->camera[i];
            memcpy(&fimc_dev->camera[i], cam, sizeof(*cam));
            fimc_dev->camera_isvalid[i] = 1;
        }
    }

从中可以看出，`fimc_init_global`函数会将fimc平台信息的所有摄像头信息拷贝到fimc的全局变量中

如如果有三个fimc的platform\_dev，那么就会调用三次`fimc_probe`函数，最后会创建三个设备节点/dev/videox，并且将所有摄像头信息保存到fimc的全局变量中

接下俩就是一系列的ioctl操作了，此部分将在稍后介绍

需要注意的是，在此之前，我们介绍的都是摄像头控制器的驱动程序，并没有涉及到真正的摄像头的驱动程序，摄像头在这里被抽象成一个v4l2\_subdev，而摄像头控制器是v4l2\_device

再继续fimc的驱动前，我们先来看一个摄像头的驱动程序

### 3.3 s5k4ba的驱动程序 ###

内核源码`s5k4ba.c`

首先看驱动的入口函数，当你拖动到最下面的时候，你会惊奇地发现，怎么没有定义`module_init`入口呢？

这是不可能地，真相只有一个，那就是在头文件中

在`v4l2-i2c-drv.h`中

struct v4l2_i2c_driver_data {
        
    	const char * const name;
    	int (*command)(struct i2c_client *client, unsigned int cmd, void *arg);
    	int (*probe)(struct i2c_client *client, const struct i2c_device_id *id);
    	int (*remove)(struct i2c_client *client);
    	int (*suspend)(struct i2c_client *client, pm_message_t state);
    	int (*resume)(struct i2c_client *client);
    	const struct i2c_device_id *id_table;
    };
    
    static struct v4l2_i2c_driver_data v4l2_i2c_data;
    static struct i2c_driver v4l2_i2c_driver;
    
    static int __init v4l2_i2c_drv_init(void)
    {
        
    	v4l2_i2c_driver.driver.name = v4l2_i2c_data.name;
    	v4l2_i2c_driver.command = v4l2_i2c_data.command;
    	v4l2_i2c_driver.probe = v4l2_i2c_data.probe;
    	v4l2_i2c_driver.remove = v4l2_i2c_data.remove;
    	v4l2_i2c_driver.suspend = v4l2_i2c_data.suspend;
    	v4l2_i2c_driver.resume = v4l2_i2c_data.resume;
    	v4l2_i2c_driver.id_table = v4l2_i2c_data.id_table;
    	return i2c_add_driver(&v4l2_i2c_driver);
    }
    
    static void __exit v4l2_i2c_drv_cleanup(void)
    {
        
    	i2c_del_driver(&v4l2_i2c_driver);
    }
    
    module_init(v4l2_i2c_drv_init);
    module_exit(v4l2_i2c_drv_cleanup);

注册了`v4l2_i2c_driver`，而`v4l2_i2c_driver`得数据来源自`v4l2_i2c_data`，所以对于编写驱动程序得人来说，就需要去填充`v4l2_i2c_data`

下面回到`s5k4ba.c`中

static const struct i2c_device_id s5k4ba_id[] = {
        
    	{
         S5K4BA_DRIVER_NAME, 0 },
    	{
         },
    };
    
    static struct v4l2_i2c_driver_data v4l2_i2c_data = {
        
    	.name = S5K4BA_DRIVER_NAME,
    	.probe = s5k4ba_probe,
    	.remove = __devexit_p(s5k4ba_remove),
    	.id_table = s5k4ba_id,
    };

当该驱动得id\_table中得名字与i2c设备的名字匹配时，就调用probe函数

static int s5k4ba_probe(struct i2c_client *client,
    			 const struct i2c_device_id *id)
    {
        
        struct v4l2_subdev *sd;
    
        sd = &state->sd;
        
        v4l2_i2c_subdev_init(sd, client, &s5k4ba_ops);
    }

probe函数会分配一个v4l2\_subdev，并调用`v4l2_i2c_subdev_init`初始化

接下来看一看`v4l2_i2c_subdev_init`

void v4l2_i2c_subdev_init(struct v4l2_subdev *sd, struct i2c_client *client,
    		const struct v4l2_subdev_ops *ops)
    {
        
        /* 设置v4l2_subdev的ops */
    	v4l2_subdev_init(sd, ops);
        
        /* 将v4l2_subdev设置为i2c_client的client_data */
        i2c_set_clientdata(client, sd);
    }

我们看以下`s5k4ba_ops`的定义

static const struct v4l2_subdev_core_ops s5k4ba_core_ops = {
        
    	.init = s5k4ba_init,	/* initializing API */
    	.s_config = s5k4ba_s_config,	/* Fetch platform data */
    	.queryctrl = s5k4ba_queryctrl,
    	.querymenu = s5k4ba_querymenu,
    	.g_ctrl = s5k4ba_g_ctrl,
    	.s_ctrl = s5k4ba_s_ctrl,
    };
    
    static const struct v4l2_subdev_video_ops s5k4ba_video_ops = {
        
    	.g_fmt = s5k4ba_g_fmt,
    	.s_fmt = s5k4ba_s_fmt,
    	.enum_framesizes = s5k4ba_enum_framesizes,
    	.enum_frameintervals = s5k4ba_enum_frameintervals,
    	.enum_fmt = s5k4ba_enum_fmt,
    	.try_fmt = s5k4ba_try_fmt,
    	.g_parm = s5k4ba_g_parm,
    	.s_parm = s5k4ba_s_parm,
    };
    
    static const struct v4l2_subdev_ops s5k4ba_ops = {
        
    	.core = &s5k4ba_core_ops,
    	.video = &s5k4ba_video_ops,
    };

定义了一系列的回调函数，估计会被v4l2\_dev调用

总结一下：`s5k4ba.`的驱动程序注册了一个i2c\_driver，当i2c\_driver遇上匹配的i2c\_client时，就会调用probe函数，probe函数会生成一个v4l2\_subdev，并设置好它的ops(一系列的回调函数)，然后将v4l2\_subdev设置为i2c\_client的clientdata

那么什么时候会有匹配的i2c\_client呢？我们接下来分析fimc的驱动

### 3.4 fimc驱动详细分析 ###

为了更加详细地分析fimc的驱动，接下来我们按照v4l2的应用编程流程来分析fimc的驱动

首先回顾以下v4l2的应用编程流程

*  查询设备功能(VIDIOC\_QUERYCAP)
 *  枚举输入设备(VIDIOC\_ENUMINPUT)
 *  设置输入设备(VIDIOC\_S\_INPUT)
 *  枚举像素格式(VIDIOC\_ENUM\_FMT)
 *  设置像素格式(VIDIOC\_S\_FMT)
 *  申请缓存(VIDIOC\_REQBUFS)
 *  映射缓存(mmap)
 *  缓存入队列(VIDIOC\_QBUF)
 *  打开流(VIDIOC\_STREAMON)
 *  等待数据可读(poll)
 *  缓存出队列(VIDIOC\_DQBUF)

下面继续分析fimc驱动

*  VIDIOC\_QUERYCAP
    
    获取设备支持的功能
    
        static int fimc_querycap(struct file *filp, void *fh,
        			 struct v4l2_capability *cap)
        {
              
        	cap->capabilities = (V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_VIDEO_OUTPUT |
        				V4L2_CAP_VIDEO_OVERLAY | V4L2_CAP_STREAMING);
        }
 *  VIDIOC\_ENUMINPUT
    
    枚举输入设备
    
    这个函数是实现v4l2\_subdev的重点
    
        int fimc_enum_input(struct file *file, void *fh, struct v4l2_input *inp)
        {
              
            struct fimc_global *fimc = get_fimc_dev();
            
            strcpy(inp->name, fimc->camera[inp->index].info->type);
        }
    
    拷贝fimc全局变量里面的摄像头信息
 *  VIDIOC\_S\_INPUT
    
        int fimc_s_input(struct file *file, void *fh, unsigned int i)
        {
              
            /* 注册子设备 */
            fimc_configure_subdev(ctrl);
        }
    
        static int fimc_configure_subdev(struct fimc_control *ctrl)
        {
              
        	struct i2c_adapter *i2c_adap;
        	struct i2c_board_info *i2c_info;
        	struct v4l2_subdev *sd;
        	unsigned short addr;
            
        	i2c_adap = i2c_get_adapter(ctrl->cam->i2c_busnum);
            
            /* 获取摄像头的i2c信息 */
            i2c_info = ctrl->cam->info;
            name = i2c_info->type;
            addr = i2c_info->addr;
            
            /* 注册v4l2_subdev */
        	sd = v4l2_i2c_new_subdev_board(&ctrl->v4l2_dev, i2c_adap,
        			name, i2c_info, &addr);
        }
    
    我们继续看`v4l2_i2c_new_subdev_board`
    
        struct v4l2_subdev *v4l2_i2c_new_subdev_board(struct v4l2_device *v4l2_dev,
        		struct i2c_adapter *adapter, const char *module_name,
        		struct i2c_board_info *info, const unsigned short *probe_addrs)
        {
              
            struct v4l2_subdev *sd = NULL;
            struct i2c_client *client;
            
            client = i2c_new_device(adapter, info); //注册i2c设备
            
            sd = i2c_get_clientdata(client); //从注册的i2c设备获取v4l2_subdev
            
            /* 注册v4l2_subdev */
            v4l2_device_register_subdev(v4l2_dev, sd)；
        }
    
    上面程序中使用`i2c_new_device`注册一个i2c设备，那么此时如果有匹配的i2c\_driver，就会调用其probe函数
    
    `sd = i2c_get_clientdata(client);`这行代码直接从注册的i2c设备获取client\_data，并指明client\_data就是v4l2\_subdev，那么一定是在i2c驱动中，生成了一个v4l2\_subdev，并将其设置到i2c\_client的client\_data里，没错，这更我们之前分析的摄像头驱动时吻合的
 *  VIDIOC\_ENUM\_FMT
    
    枚举像素格式
    
        static const struct v4l2_fmtdesc capture_fmts[] = {
              
        	{
              
        		.index		= 0,
        		.type		= V4L2_BUF_TYPE_VIDEO_CAPTURE,
        		.flags		= FORMAT_FLAGS_PACKED,
        		.description	= "RGB-5-6-5",
        		.pixelformat	= V4L2_PIX_FMT_RGB565,
        	}, {
              
        		.index		= 2,
        		.type		= V4L2_BUF_TYPE_VIDEO_CAPTURE,
        		.flags		= FORMAT_FLAGS_PACKED,
        		.description	= "YUV 4:2:2 packed, YCbYCr",
        		.pixelformat	= V4L2_PIX_FMT_YUYV,
        	}, {
              
        		.index		= 3,
        		.type		= V4L2_BUF_TYPE_VIDEO_CAPTURE,
        		.flags		= FORMAT_FLAGS_PACKED,
        		.description	= "YUV 4:2:2 packed, CbYCrY",
        		.pixelformat	= V4L2_PIX_FMT_UYVY,
        	},
            ...
        };
        ...
        int fimc_enum_fmt_vid_capture(struct file *file, void *fh,
        					struct v4l2_fmtdesc *f)
        {
              
            memcpy(f, &capture_fmts[i], sizeof(*f));
        }
 *  VIDIOC\_S\_FMT
    
    设置像素格式
    
        int fimc_s_fmt_vid_capture(struct file *file, void *fh, struct v4l2_format *f)
        {
              
            struct fimc_capinfo *cap; //捕获设备的信息
            
            ctrl->cap = kmalloc(sizeof(*cap), GFP_KERNEL);
        	cap = ctrl->cap;
        	memcpy(&cap->fmt, &f->fmt.pix, sizeof(cap->fmt)); 
        
        	depth = fimc_fmt_depth(ctrl, f);
        }
    
    设置像素格式就是将像素格式拷贝到fimc\_capinfo中
    
    fimc\_capinfo时描述的是捕获设备的信息，如下
    
        struct fimc_capinfo {
              
        	struct v4l2_cropcap	cropcap;
        	struct v4l2_rect	crop;
        	struct v4l2_pix_format	fmt;
        	struct fimc_buf_set	bufs[FIMC_CAPBUFS]; //视频缓存
        	struct list_head	inq;
        	int			outq[FIMC_PHYBUFS]; //dma地址
        	int			nr_bufs;
        	int			irq;
        	int			lastirq;
        
        	/* flip: V4L2_CID_xFLIP, rotate: 90, 180, 270 */
        	u32			flip;
        	u32			rotate;
        };
 *  VIDIOC\_REQBUFS
    
    申请缓存
    
        int fimc_reqbufs_capture(void *fh, struct v4l2_requestbuffers *b)
        {
              
            int size[4] = {
               0, 0, 0, 0}; // 颜色分量的大小
            
            /* 计算像素各颜色分量的大小 */
            switch()
            {
              
            ...
        	case V4L2_PIX_FMT_YUV420:
        		size[0] = cap->fmt.width * cap->fmt.height;
        		size[1] = cap->fmt.width * cap->fmt.height >> 2;
        		size[2] = cap->fmt.width * cap->fmt.height >> 2;
        		size[3] = 16; /* Padding buffer */
            	break;
            ...
            }
            
            /* 分配dma缓存 */
            fimc_alloc_buffers(ctrl, size, align);
        }
    
    为cap中的buf分配缓存
    
        static int fimc_alloc_buffers(struct fimc_control *ctrl, int size[], int align)
        {
              
            for()
            {
              
                fimc_dma_alloc(ctrl, &cap->bufs[i], plane, align);
            }
        }
 *  mmap
    
    内存映射
    
        static int fimc_mmap(struct file *filp, struct vm_area_struct *vma)
        {
              
            fimc_mmap_cap(filp, vma);
        }
    
        static inline int fimc_mmap_cap(struct file *filp, struct vm_area_struct *vma)
        {
              
            pfn = __phys_to_pfn(ctrl->cap->bufs[idx].base[0]);
            remap_pfn_range(vma, vma->vm_start, pfn, size, vma->vm_page_prot);
        }
 *  VIDIOC\_QBUF
    
    缓存入队列
    
        static int fimc_qbuf(struct file *filp, void *fh, struct v4l2_buffer *b)
        {
              
            fimc_qbuf_capture(fh, b);
        }
    
        int fimc_qbuf_capture(void *fh, struct v4l2_buffer *b)
        {
              
            fimc_add_inqueue(ctrl, b->index);
        }
    
    将指定的buf加入队列中
    
        static int fimc_add_inqueue(struct fimc_control *ctrl, int i)
        {
              
            list_add_tail(&cap->bufs[i].list, &cap->inq);
        }
 *  poll
    
    等待数据准备好
    
        static u32 fimc_poll(struct file *filp, poll_table *wait)
        {
              
            /* 加入等待队列 */
            poll_wait(filp, &ctrl->wq, wait);
        }
 *  唤醒
    
    什么会唤醒等待队列？
    
    fimc\_dev.c的probe函数中，一开始就申请了中断，前面在分析的时候并没有仔细看，现在来好好看一看
    
    当有一帧数据准备完成的时候，就会调用fimc的中断函数，中断会唤醒等待队列，poll就会返回
    
        static irqreturn_t fimc_irq(int irq, void *dev_id)
        {
              
            fimc_irq_cap(ctrl);
        }
    
        static inline void fimc_irq_cap(struct fimc_control *ctrl)
        {
              
        	fimc_hwset_clear_irq(ctrl); //清中断
            
            /* 唤醒等待队列 */
            wake_up(&ctrl->wq);
        }
 *  VIDIOC\_DQBUF
    
    出队列
    
    在poll返回后，就调用dqbuf获取缓存
    
        static int fimc_dqbuf(struct file *filp, void *fh, struct v4l2_buffer *b)
        {
              
        	fimc_dqbuf_capture(fh, b);
        }
    
        int fimc_dqbuf_capture(void *fh, struct v4l2_buffer *b)
        {
              
            /* 找到准备好的ping-pong */
            pp = ((fimc_hwget_frame_count(ctrl) + 2) % 4); 
            
            b->index = cap->outq[pp];
            
            /* 重新设置ping-pong的buf */
            fimc_add_outqueue(ctrl, pp);
        }
    
    这里说一下什么是ping-pong
    
    ping-pong是一个硬件上的东西，视频采集需要一个缓存区，可以把ping-pong看作是一个循环队列，以S5PV210为例，有四个ping-pong，每个ping-pong都存放着目的buf的地址，每当有图像数据准备好，就会通过dma存到对应的ping-pong所指定的目的地址处

[Linux_v4l2]: https://blog.csdn.net/weixin_42462202/article/details/96826526
[Linux_v4l2 1]: https://blog.csdn.net/weixin_42462202/article/details/99680969
[Linux]: https://blog.csdn.net/weixin_42462202/article/details/99719750
[Linux_fimc]: https://blog.csdn.net/weixin_42462202/article/details/99765607
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