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

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Message-ID: <51750EB9.3020301@free-electrons.com>
Date:	Mon, 22 Apr 2013 12:19:37 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Marek Vasut <marex@...x.de>
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>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND] video: mxsfb: Fix colors display on lower color
 depth

Hi Marek,

Le 22/04/2013 11:16, Marek Vasut a écrit :
> 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>
> 
> Did you receive my latest email? Check M28EVK (imx28-m28evk.dts), it uses 18bit 
> LCD and works without this patch I think.

Thanks for the pointer. You mentionned in your other mail that it was
wired on 24bits but that the screen is actually 18 bits. I went to
search for the schematics to look at the wirings to see what could
differ, but I couldn't find any for the M28EVK. Are they publicly available?

Thanks,
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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