Re: OMAPFB: CMA allocation failures

[Ivajlo Dimitrov <ivo.g.dimitrov.75@gmail.com>]

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----- Original Message ----- 
From: "Ивайло Димитров" <freemangordon@abv.bg>
To: "Tomi Valkeinen" <tomi.valkeinen@ti.com>
Cc: <minchan@kernel.org>; <pavel@ucw.cz>; <sre@debian.org>; 
<pali.rohar@gmail.com>; <pc+n900@asdf.org>; <linux-kernel@vger.kernel.org>; 
<linux-mm@kvack.org>
Sent: Tuesday, November 05, 2013 9:55 PM
Subject: Re: OMAPFB: CMA allocation failures


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> >-------- Оригинално писмо --------
> >От:  Tomi Valkeinen
> >Относно: Re: OMAPFB: CMA allocation failures
> >До: Ивайло Димитров
> >Изпратено на: Сряда, 2013, Октомври 30 14:19:32 EET
> >
> >I really dislike the idea of adding the omap vram allocator back. Then
> >again, if the CMA doesn't work, something has to be done.
> >
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> If I got Minchan Kim's explanation correctly, CMA simply can't be used
> for allocation of framebuffer memory, because it is unreliable.
>
> >Pre-allocating is possible, but that won't work if there's any need to
> >re-allocating the framebuffers. Except if the omapfb would retain and
> >manage the pre-allocated buffers, but that would just be more or less
> >the old vram allocator again.
> >
> >So, as I see it, the best option would be to have the standard dma_alloc
> >functions get the memory for omapfb from a private pool, which is not
> >used for anything else.
> >
> >I wonder if that's possible already? It sounds quite trivial to me.
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> dma_alloc functions use either CMA or (iirc) get_pages_exact if CMA is
> disabled. Both of those fail easily. AFAIK there are several
> implementations with similar functionality, like CMEM and ION but
> (correct me if I am wrong) neither of them is upstreamed. In the
> current kernel I don't see anything that can be used for the purpose
> of reliable allocation of big chunks of contiguous memory.
> So, something should be done, but honestly, I can't think of anything
> but bringing VRAM allocator back. Not that I like the idea of bringing
> back ~700 lines of code, but I see no other option if omapfb driver is
> to be actually useful.
>
> Regards,
> Ivo