Re: [PATCH] drm/vc4: plane: Expand the lower bits using the LSB

Maxime Ripard maxime.ripard@bootlin.com writes:

The vc4 HVS uses an internal RGB888 representation of the frames, and will by default expand formats using a lower depth using zeros.

This causes an issue when we try to use other compositing software such as pixman that seems to be filling the missing bits using the format least significant bit value. As such, this prevents us from checking the display output in a reliable way.

I don't think this is the right expansion function, though? My understanding of proper unorm expansion, and what pixman's unorm_to_unorm() does, is that you replicate the value in the missing bits until you've filled them all (so SCALER_CTL0_EXPAND_REPEAT)