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

[Eric Anholt]

Maxime Ripard <maxime.ripard at 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)
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