Control IMX219 camera exposure

#1

I have been using an IMX219 sensor with the Radxa NX5. In general it is working very good.

I am looking for a way to alter the exposure of the camera in conjunction with the rockchip isp. What is the best way to do this in general? Is it possible to supply auto exposure tuning files for rkisp as is the case with raspberry pi?

Exposure of the sensor itself can be set. For example via v4l2-ctl

# v4l2-ctl --list-ctrls  -d /dev/v4l-subdev2
User Controls
               exposure 0x00980911 (int)    : min=0 max=4095 step=1 default=1575 value=100
                   gain 0x00980913 (int)    : min=256 max=43663 step=1 default=256 value=256
        horizontal_flip 0x00980914 (bool)   : default=0 value=0
          vertical_flip 0x00980915 (bool)   : default=0 value=0

Image Source Controls
          vertical_blanking 0x009e0901 (int)    : min=686 max=686 step=1 default=686 value=686
        horizontal_blanking 0x009e0902 (int)    : min=1524 max=1524 step=1 default=1524 value=1524
              analogue_gain 0x009e0903 (int)    : min=256 max=2816 step=1 default=512 value=1536

Image Processing Controls
             link_frequency 0x009f0901 (intmenu): min=0 max=0 default=0 value=0 (456000000 0x1b2e0200)
                 pixel_rate 0x009f0902 (int64)  : min=0 max=182463120 step=1 default=182463120 value=182463120 flags=read-only
               test_pattern 0x009f0903 (menu)   : min=0 max=13 default=0 value=0 (Disabled)

    # v4l2-ctl --set-ctrl 'exposure=200' -d /dev/v4l-subdev2

This setting will however be overwritten by the ISP.
As far as I know autoexposure cannot be disabled without disabling the ISP completely?
There is no v4l user control to disable it as is often the case.

# v4l2-ctl --list-ctrls  -d /dev/v4l-subdev3

Image Processing Controls
             pixel_rate 0x009f0902 (int64)  : min=0 max=1000000000 step=1 default=1000000000 value=182463120 flags=read-only, volatile

Any tips or links pointing me in the right search direction would be greatly appreciated.

For my particular use case right now it would be sufficient to only limit the maximum exposure. I could do this by modifying the imx219 v4l exposure control in the driver. But I am curious to find a cleaner and more general approach.