Re: [PATCH] ARM: omapfb: Add early framebuffer memory allocator

From: Ivaylo Dimitrov
Date: Fri Dec 27 2013 - 11:35:55 EST

On 27.12.2013 11:48, Pavel Machek wrote:
On Thu 2013-12-26 01:12:39, Ivaylo Dimitrov wrote:
From: Ivaylo Dimitrov <freemangordon@xxxxxx>

On memory limited devices, CMA fails easily when asked to allocate big
chunks of memory like framebuffer memory needed for video playback.

Add boot parameter "omapfb_memsize" which allocates memory to be used
as dma coherent memory, so dma_alloc_attrs won't hit CMA allocator when
trying to allocate memory for the framebuffers

Signed-off-by: Ivaylo Dimitrov <freemangordon@xxxxxx>
Hmm, would it make sense to add a parameter to reserve certain ammount
of memory for CMA? omapfb is probably not the only user hitting

But that would mean that one must have CMA enabled to use that functionality and it is an additional memory overhead. Also, I don't think we will have much of a benefit of that - for video playback we'll still have to preallocate the same amount of RAM as now - but with the additional overhead of page migration when that RAM becomes needed by DSP and OMAPFB. However, even if such functionality is someday implemented in CMA, it doesn't conflict with the proposed patch - by simply not preallocating memory for omapfb, one will automatically use it.

BTW there is CMEM driver (not upstreamed afaik) which does exactly that - it manages a contiguous ("stolen")memory pool. No idea how easy it would be to merge CMEM into CMA. Neither I am the right guy for the task, IMO :)

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