It turns out that local alpha value of the secondary input is set to
0xFF by the hardware if the secondary input is from scaler(hscaler or
vscaler). This makes the layer on this secondary input accidentally
cover the layer with higher z-order(if it exists), even though the
layer with lower z-order doesn't supply local alpha. This patch zeros
the secondary local alpha value to prevent the issue from happening.
Users are unlikely to expect local alpha to be correctly scaled, so
it looks fine to simply zero the alpha. If we find the unlikely case,
the KMS driver may later explicitly do atomic check to invalidate the case.
Signed-off-by: Liu Ying <victor.liu@nxp.com>
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