Re: [PATCH 3/3] drm: omapdrm: Do no allocate non-scanout GEMs through DMM/TILER

[Ivaylo Dimitrov]

On 17.02.22 г. 14:46 ч., Tomi Valkeinen wrote:
> Hi,
>
> On 19/01/2022 12:23, Ivaylo Dimitrov wrote:
> > On devices with DMM, all allocations are done through either DMM or 
> > TILER.
> > DMM/TILER being a limited resource means that such allocations will start
> > to fail before actual free memory is exhausted. What is even worse is 
> > that
> > with time DMM/TILER space gets fragmented to the point that even if we 
> > have
> > enough free DMM/TILER space and free memory, allocation fails because 
> > there
> > is no big enough free block in DMM/TILER space.
> >
> > Such failures can be easily observed with OMAP xorg DDX, for example -
> > starting few GUI applications (so buffers for their windows are 
> > allocated)
> > and then rotating landscape<->portrait while closing and opening new
> > windows soon results in allocation failures.
> >
> > Fix that by mapping buffers through DMM/TILER only when really needed,
> > like, for scanout buffers.
>
> Doesn't this break users that get a buffer from omapdrm and expect it to 
> be contiguous?

If you mean dumb buffer, then no, this does not break users as dumb 
buffers are allocated as scanout:

https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/omapdrm/omap_gem.c#L603

If you mean omap_bo allocated buffers, then if users want 
linear(scanout) buffer, then they request it explicitly by passing 
OMAP_BO_SCANOUT.

Ivo