exposure-auto setting fails

I am trying to tune a C920 webcam for picture quality using v4l2-ctl utility on Ubuntu PC. I am unable to set exposure_auto to'Auto' mode, but I am able to set it to'Manual Mode'or in'Aperture Priority Mode'. Any clues?

lenovo@ubuntu:~$ v4l2-ctl -d /dev/video1 -c exposure_auto=0
VIDIOC_S_CTRL: failed: Input/output error
exposure_auto: Input/output error

Following are the settings dump of C920 connected to my ubuntu:

• brightness (int) : min=0 max=255 step=1 default=128 value=128
• contrast (int) : min=0 max=255 step=1 default=128 value=128
• saturation (int) : min=0 max=255 step=1 default=128 value=128
• white_balance_temperature_auto (bool) : default=1 value=1
• gain (int) : min=0 max=255 step=1 default=0 value=0
• power_line_frequency (menu) : min=0 max=2 default=2 value=2
• white_balance_temperature (int) : min=2000 max=6500 step=1 default=4000 value=4000
• sharpness (int) : min=0 max=255 step=1 default=128 value=128
• backlight_compensation (int) : min=0 max=1 step=1 default=0 value=0
• exposure_auto (menu) : min=0 max=3 default=3 value=3 (0: Auto Mode 1: Manual Mode
  2: Shutter Priority Mode
  3: Aperture Priority Mode)
• exposure_absolute (int) : min=3 max=2047 step=1 default=250 value=250
• exposure_auto_priority (bool) : default=0 value=1
• focus_absolute (int) : min=0 max=250 step=5 default=0 value=0
• focus_auto (bool) : default=1 value=1
• zoom_absolute (int) : min=100 max=500 step=1 default=100 value=100

That usually happens when you try to manually set a setting which is currently controlled by some other automatic. Try toggling ''exposure_auto_priority''to see if that looses the grip of the auto algorithm on that particular setting.

For me, for example, setting''white_balance_temperature_auto''to 0 allowed me to manually set ''white_balance_temperature'' which resulted in"failed: Input/output error"before.

Using

v4l2-ctl -d /dev/video1 -c exposure_auto=1

instead of exposure_auto = 0, you can set exposure to manual then set exposure_absolute to change the value.