linux-kernel - Re: Proposal for a low-level Linux display framework

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Date:	Thu, 15 Sep 2011 19:46:36 +0000
From:	Florian Tobias Schandinat <FlorianSchandinat@....de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Keith Packard <keithp@...thp.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linaro-dev@...ts.linaro.org,
	"Clark\, Rob" <rob@...com>, Archit Taneja <archit@...com>
Subject: Re: Proposal for a low-level Linux display framework

On 09/15/2011 07:05 PM, Alan Cox wrote:
>> What is your problem with discontigous framebuffers? (I assume discontigous
>> refers to the pages the framebuffer is composed of)
>> Sounds to me like you should implement your own fb_mmap and either map it
>> contigous to screen_base or implement your own fb_read/write.
>> In theory you could even have each pixel at a completely different memory
>> location although some userspace wouldn't be happy when it could no longer mmap
>> the framebuffer.
> 
> The mmap side is trivial, the problem is that the fb layer default
> implementations of blits, fills etc only work on a kernel linear frame
> buffer. And (for example) there is not enough linear stolen memory on
> some Intel video for a 1080p console on HDMI even though the hardware is
> perfectly capable of using an HDTV as its monitor. Nor - on a 32bit box-
> is there enough space to vremap it.

Okay, I see your problem. It's a bit strange you don't have acceleration. I
guess you need either your own implementation of those or adding function
pointers like fb_read/write just without the __user and use those instead of
direct memory access in the cfb* implementation if screen_base is NULL. Does not
sound like a big problem to me, but pretty inefficient, so probably copying the
existing ones and adjusting it to your needs would be preferred (just like the
sys* implementations exist).


Best regards,

Florian Tobias Schandinat
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