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

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Message-ID: <20130418144838.GD2222@S2101-09.ap.freescale.net>
Date:	Thu, 18 Apr 2013 22:48:39 +0800
From:	Shawn Guo <shawn.guo@...aro.org>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	Fabio Estevam <fabio.estevam@...escale.com>,
	Marek Vasut <marex@...x.de>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Thomas Petazzoni <thomas@...e-electrons.com>,
	Brian Lilly <brian@...stalfontz.com>,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	<linux-fbdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] video: mxsfb: Fix colors display on lower color depth

Copy Sascha.

Shawn

On Thu, Apr 18, 2013 at 11:23:52AM +0200, 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.
> 
> 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>
> ---
>  drivers/video/mxsfb.c |    5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/drivers/video/mxsfb.c b/drivers/video/mxsfb.c
> index 755556c..2cfaf8b 100644
> --- a/drivers/video/mxsfb.c
> +++ b/drivers/video/mxsfb.c
> @@ -424,11 +424,6 @@ static int mxsfb_set_par(struct fb_info *fb_info)
>  			return -EINVAL;
>  		case STMLCDIF_16BIT:
>  		case STMLCDIF_18BIT:
> -			/* 24 bit to 18 bit mapping */
> -			ctrl |= CTRL_DF24; /* ignore the upper 2 bits in
> -					    *  each colour component
> -					    */
> -			break;
>  		case STMLCDIF_24BIT:
>  			/* real 24 bit */
>  			break;
> -- 
> 1.7.10.4
> 

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