RK3568平台（camera篇）V4L2查询获取设置设备

一.查询设备能力VIDIOC_QUERYCAP

struct v4l2_capability cap;
ioctl(fd, VIDIOC_QUERYCAP, &cap)

struct v4l2_capability 结构体描述了视频采集设备的 driver 信息。

struct v4l2_capability
{
__u8 driver[16]; // 驱动名字
__u8 card[32]; // 设备名字
__u8 bus_info[32]; // 设备在系统中的位置
__u32 version; // 驱动版本号
__u32 capabilities; // 设备支持的操作
__u32 reserved[4]; // 保留字段
};

video注册的时候fops是v4l2_fops，所以会调用到v4l2_fops.unlocked_ioctl 也就是 v4l2_ioctl

v4l2_ioctl中调用到 vdev->fops->unlocked_ioctl，vdev->fops对于vivi驱动的vivi_fops，所以unlocked_ioctl就是video_ioctl2

其中VIDIOC_QUERYCAP对应 v4l_querycap。

static int v4l_querycap(const struct v4l2_ioctl_ops *ops,struct file *file, void *fh, void *arg)
{struct v4l2_capability *cap = (struct v4l2_capability *)arg;struct video_device *vfd = video_devdata(file);int ret;cap->version = LINUX_VERSION_CODE;cap->device_caps = vfd->device_caps;cap->capabilities = vfd->device_caps | V4L2_CAP_DEVICE_CAPS;/** 对应vivi驱动的 vidioc_querycap*/ret = ops->vidioc_querycap(file, fh, cap);cap->capabilities |= V4L2_CAP_EXT_PIX_FORMAT;/** Drivers MUST fill in device_caps, so check for this and* warn if it was forgotten.*/WARN(!(cap->capabilities & V4L2_CAP_DEVICE_CAPS) ||!cap->device_caps, "Bad caps for driver %s, %x %x",cap->driver, cap->capabilities, cap->device_caps);cap->device_caps |= V4L2_CAP_EXT_PIX_FORMAT;return ret;
}

vivi驱动vidioc_querycap源码如下

static int vidioc_querycap(struct file *file, void  *priv,struct v4l2_capability *cap)
{struct vivi_dev *dev = video_drvdata(file);strcpy(cap->driver, "vivi");strcpy(cap->card, "vivi");/** 这里加深一下理解* dev->v4l2_dev.name 是什么？* vivi驱动中有这样一句代码* snprintf(dev->v4l2_dev.name, sizeof(dev->v4l2_dev.name),"%s-%03d", VIVI_MODULE_NAME, inst);* "vivi-000" "vivi-001" 这种名字*/strlcpy(cap->bus_info, dev->v4l2_dev.name, sizeof(cap->bus_info));cap->version = VIVI_VERSION;/** 驱动表示支持capture，streaming及read write*/    cap->capabilities = V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_STREAMING | \V4L2_CAP_READWRITE;return 0;
}

从capabilities的返回值能知道这个设备所支持的功能。

判断设备是否支持拍照功能：

if (ioctl(fd_v4l, VIDIOC_QUERYCAP, &cap) == 0)
{printf("cap=0x%x\n", cap.capabilities);if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)){printf("%s not support v4l2 capture device.\n", dev_name);return -1;}
}
else
{close(fd_v4l);return -1;
}

二.设置输入设备VIDIOC_S_INPUT

一个video设备节点可能对应多个视频源，所以需要指定输入的设备。

input.index = index; //指定输入设备
if (ioctl(fd, VIDIOC_S_INPUT, &input) < 0)

设备输入的设备为设备0：

struct v4l2_input inp;
inp.index = 0;
if (ioctl(fd_v4l, VIDIOC_S_INPUT, &inp) < 0)
{printf("VIDIOC_S_INPUT error.!");return -1;
}

对应vivi的vidioc_s_input

static int vidioc_s_input(struct file *file, void *priv, unsigned int i)
{struct vivi_dev *dev = video_drvdata(file);if (i >= NUM_INPUTS)return -EINVAL;dev->input = i;precalculate_bars(dev);precalculate_line(dev);return 0;
}

三.获取设置支持的视频格式VIDIOC_G_FMT

struct v4l2_format {enum v4l2_buf_type type;union {struct v4l2_pix_format         pix;     /* V4L2_BUF_TYPE_VIDEO_CAPTURE */struct v4l2_window             win;     /* V4L2_BUF_TYPE_VIDEO_OVERLAY */struct v4l2_vbi_format         vbi;     /* V4L2_BUF_TYPE_VBI_CAPTURE */struct v4l2_sliced_vbi_format  sliced;  /* V4L2_BUF_TYPE_SLICED_VBI_CAPTURE */__u8   raw_data[200];                   /* user-defined */} fmt;
};
其中
enum v4l2_buf_type {V4L2_BUF_TYPE_VIDEO_CAPTURE        = 1,V4L2_BUF_TYPE_VIDEO_OUTPUT         = 2,V4L2_BUF_TYPE_VIDEO_OVERLAY        = 3,...V4L2_BUF_TYPE_PRIVATE              = 0x80,
};struct v4l2_pix_format {__u32                   width;__u32                   height;__u32                   pixelformat;enum v4l2_field         field;__u32                   bytesperline;   /* for padding, zero if unused */__u32                   sizeimage;enum v4l2_colorspace    colorspace;__u32                   priv;           /* private data, depends on pixelformat */
};

通过VIDIOC_G_FMT获取输入设备的宽高：

if (ioctl(fd_v4l, VIDIOC_G_FMT, &fmt) < 0)
{printf("get format failed\n");goto fail;
}camera_width  = fmt.fmt.pix_mp.width;
camera_height = fmt.fmt.pix_mp.height;

四.设置视频格式VIDIOC_S_FMT

memset(&v4l2_fmt, 0, sizeof(struct v4l2_format));
v4l2_fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; 
v4l2_fmt.fmt.pix.width = width; //宽度
v4l2_fmt.fmt.pix.height = height; //高度
v4l2_fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV; //像素格式
v4l2_fmt.fmt.pix.field = V4L2_FIELD_ANY;if (ioctl(fd, VIDIOC_S_FMT, &v4l2_fmt) < 0)

这里对应vivi驱动的vidioc_s_fmt_vid_cap

static int vidioc_s_fmt_vid_cap(struct file *file, void *priv,struct v4l2_format *f)
{struct vivi_dev *dev = video_drvdata(file);struct vb2_queue *q = &dev->vb_vidq;int ret = vidioc_try_fmt_vid_cap(file, priv, f);if (ret < 0)return ret;/** vb2_is_streaming 判断vb2_is_streaming的值，后面的分析我们会看到这个值* 的变化，这里认为值为0，if不满足*/if (vb2_is_streaming(q)) {dprintk(dev, 1, "%s device busy\n", __func__);return -EBUSY;}dev->fmt = get_format(f);dev->width = f->fmt.pix.width;dev->height = f->fmt.pix.height;dev->field = f->fmt.pix.field;return 0;
}

五.获取Stream信息VIDIOC_G_PARM

struct v4l2_streamparm Stream_Parm;
memset(&Stream_Parm, 0, sizeof(struct v4l2_streamparm));
Stream_Parm.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
io_rel = ioctl(Handle, VIDIOC_G_PARM, &Stream_Parm);

struct v4l2_streamparm
{
enum v4l2_buf_type type;
union
{
struct v4l2_captureparm capture;
struct v4l2_outputparm output;
__u8 raw_data[200];
} parm;
};因为是Camera， 所以使用capture。
struct v4l2_captureparm
{
__u32 capability;   // 是否可以被timeperframe控制帧数。可以则：V4L2_CAP_TIMEPERFRAME
__u32 capturemode;  // 是否为高清模式。如果是则设置为：V4L2_MODE_HIGHQUALITY。 高清模式会牺牲其它信息。通常设置为0。
struct v4l2_fract timeperframe;  //帧数。
__u32 extendedmode; //定制的。如果不支持，设置为0
__u32 readbuffers;
__u32 reserved[4];
};struct v4l2_fract {
__u32 numerator;   // 分子。 例：1
__u32 denominator; // 分母。 例：30
};

六.设置Stream信息VIDIOC_S_PARM

struct v4l2_streamparm streamparm = {0};
streamparm.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
ioctl(fd, VIDIOC_G_PARM, &streamparm);
if (V4L2_CAP_TIMEPERFRAME & streamparm.parm.capture.capability) 
{streamparm.parm.capture.timeperframe.numerator = 1;streamparm.parm.capture.timeperframe.denominator = 30;//30fpsif (0 > ioctl(fd, VIDIOC_S_PARM, &streamparm)) {printf("ioctl error: VIDIOC_S_PARM");return -1;}
}