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SubjectRe: OMAPFB: CMA allocation failures





>-------- 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.
>

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.

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
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