[PATCH RESEND] video: mxsfb: Fix colors display on lower color depth

[jbe@pengutronix.de (Juergen Beisert)]

Hi Maxime,

Maxime Ripard wrote:
> The current code always registers as a 32 bits display, and uses the
> hardware to drop the MSB of each color to abjust to the interface width
> used by the panel.
>
> This results on 18 bits (and probably 16 bits display as well) in colors
> being displayed poorly, because the MSB are obviously the most important
> bits for each color definition.

But the "def_rgb666" bitfield description reports correctly to use bit 0..5 
for each colour component in this mode. Maybe your userland program has a bug 
and forgets to honor the bitfield description?

> The default controller behaviour when using an interface width smaller
> than the color depth is to drop the LSBs of each color, which makes more
> sense because you lose the least important part of the color definition.
>
> So, to fix the colors display, just get back to the default controller
> behaviour.

If you do this change, you also must adapt the "def_rgb666" bitfield 
description.
This structure currently reports the lower 6 bits to be used for this mode:
  blue -> 0..5 (skip 6/7)
  green -> 8..13 (skip 14/15)
  red -> 16..21 (skip 22/23).

> [...]

jbe

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