linux-kernel - Re: ATI Radeon DIRECTCOLOR -> TRUECOLOR patch

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Message-ID: <49A5B17C.9060705@nerdgrounds.com>
Date:	Wed, 25 Feb 2009 13:00:44 -0800
From:	Jonathan Campbell <jon@...dgrounds.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
CC:	David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org
Subject: Re: ATI Radeon DIRECTCOLOR -> TRUECOLOR patch

  But at the very least could radeonfb default to truecolor-like 
behavior and leave the bizarre ramp mapping for programs that want it?
> On Wed, 2009-02-25 at 03:57 -0800, David Miller wrote:
>> From: Jonathan Campbell <jon@...dgrounds.com>
>> Date: Wed, 25 Feb 2009 03:24:35 -0800
>>
>> [ Ben H. is the Radeon driver maintainer, as listed in
>>   linux/MAINTAINERS, you might want to CC: him ]
>>
>>> I don't know about you but when I ask the framebuffer to set up
>>> 16-bit or 32-bit RGB modes I expect a video mode to be set up with
>>> R, G, and B mapped linearly so that I can display images properly,
>>> not some odd "directcolor" mode that seems to serve no other purpose
>>> than to avoid a few shifts converting the fbcon palette to an RGB
>>> triplet.
>> It might be using DIRECTCOLOR for compatibility with openfirmware,
>> BOOTX, or similar on PowerPC.
>
> Hrm, the kernel fb layer does seem to do strange things with the palette
> for >8bpp stuff indeed. I'm not entirely sure why.
>
> The problem if you switch to truecolor is that you remove the ability to
> set the gamma ramp completely which some apps use.
>
> Normally, I'd say it's the responsibility of your application, when it's
> displaying pictures, to set an appropriate cmap. If you don't like the
> one set by fbcon for displaying text, just set another one. Ie. You
> aren't -supposed- to mix graphics and fbcon text from an application...
> if you're going to blast to the fb, you should switch to KD_GRAPHICS (ie
> take ownership of the VT) and set a linear ramp yourself.
>
> Cheers,
> Ben.
>
>
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