[FAQ] How can I change the sensor parameters using v4l2-ctl?

The /dev/videoX nodes associated with the CSI2-RX are just video capture devices used to allocate, enqueue and dequeue frame buffers and start the DMA transfer. They are not directly associated with the sensor. There are no controls required from the user space for these nodes. Therefore, "v4l2-ctl -d /dev/videoX --list-ctrls" won't return anything.

For example, on AM62A, there are 6 video nodes under j721e-csi2rx (the CSI2-RX driver), and none of these nodes has any controls from the user space:

root@am62axx-evm:~# v4l2-ctl --list-devices
j721e-csi2rx (platform:30102000.ticsi2rx):
        /dev/video3
        /dev/video4
        /dev/video5
        /dev/video6
        /dev/video7
        /dev/video8
        /dev/media0

wave5-dec (platform:30210000.video-codec):
        /dev/video0
        /dev/video1

e5010 (platform:fd20000.jpeg-encoder):
        /dev/video2

root@am62axx-evm:~# v4l2-ctl -d /dev/video3 --list-ctrls
root@am62axx-evm:~# v4l2-ctl -d /dev/video4 --list-ctrls
root@am62axx-evm:~#

To control the parameters of a sensor, the /dev/v4l-subdevX node created by the sensor driver should be used instead. To find the right subdev number, run command "media-ctl -p -d /dev/mediaX" where /dev/mediaX is the media device node created by the CSI2-Rx driver. For example, below is what should be displayed for IMX219 on AM62A:

root@am62axx-evm:~# media-ctl -p -d/dev/media0

...

- entity 15: imx219 4-0010 (1 pad, 1 link, 0 routes)
             type V4L2 subdev subtype Sensor flags 0
             device node name /dev/v4l-subdev2
        pad0: Source
                [stream:0 fmt:SRGGB8_1X8/1920x1080 field:none colorspace:raw xfer:none quantization:full-range
                 crop.bounds:(8,8)/3280x2464
                 crop:(688,700)/1920x1080]
                -> "cdns_csi2rx.30101000.csi-bridge":0 [ENABLED,IMMUTABLE]

...

Then use the sensor's subdev node to change parameters:

root@am62axx-evm:~# v4l2-ctl -d /dev/v4l-subdev2 --list-ctrls

User Controls

                       exposure 0x00980911 (int)    : min=4 max=1759 step=1 default=1600 value=1600
                horizontal_flip 0x00980914 (bool)   : default=0 value=0 flags=modify-layout
                  vertical_flip 0x00980915 (bool)   : default=0 value=0 flags=modify-layout

...

root@am62axx-evm:~# v4l2-ctl -d /dev/v4l-imx219-subdev0 --set-ctrl exposure=40

root@am62axx-evm:~# v4l2-ctl -d /dev/v4l-imx219-subdev0 --set-ctrl digital_gain=4095

For other common problems related to CSI camera, please refer to this FAQ:

• [FAQ] Most common problems encountered when developing camera applications on the AM6x