linux-kernel - Re: [PATCH] video: mxsfb: Fix colors display on lower color depth

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Message-Id: <201304181600.27813.marex@denx.de>
Date:	Thu, 18 Apr 2013 16:00:27 +0200
From:	Marek Vasut <marex@...x.de>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	Shawn Guo <shawn.guo@...aro.org>,
	linux-arm-kernel@...ts.infradead.org,
	Fabio Estevam <fabio.estevam@...escale.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Thomas Petazzoni <thomas@...e-electrons.com>,
	Brian Lilly <brian@...stalfontz.com>,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] video: mxsfb: Fix colors display on lower color depth

Dear Maxime Ripard,

> 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.
> 
> 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.
> 
> Signed-off-by: Maxime Ripard <maxime.ripard@...e-electrons.com>

Isn't this what M28EVK is doing already? This was last tested on 3.9-rc3 I 
think:

bits-per-pixel = <16>;
bus-width = <18>;

But it's also true we have all 24 data lines routed to the LCD.

Best regards,
Marek Vasut
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