The driver doesn't set an initial video format until s_input is called:
$ v4l2-ctl -d /dev/v4l-touch0 --get-input
Video input : 0 (Normalized 16-Bit Image: ok)
$ v4l2-ctl -d /dev/v4l-touch0 --get-fmt-video
Width/Height : 0/0
Pixel Format : ''
[...]
$ v4l2-ctl -d /dev/v4l-touch0 --set-input 0
Video input set to 0 (Normalized 16-Bit Image: Touch, ok)
$ v4l2-ctl -d /dev/v4l-touch0 --get-fmt-video
Width/Height : 71/40
Pixel Format : 'TD16'
[...]
To fix this, initialize the video format to input 0 during probe.
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
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