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

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Date:	Mon, 22 Apr 2013 16:30:48 +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>,
	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

Dear Maxime Ripard,

> 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?

Yes, [1] page 6 .

[1] http://www.denx-cs.de/doku/sites/default/files/M28EVK_V20_0.pdf

Best regards,
Marek Vasut
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