[Intel-gfx] [RFC PATCH 5/5] drm/i915/flat-CCS: handle creation and destruction of flat CCS bo's

[Thomas Hellström]

On Mon, 2022-01-24 at 17:24 +0100, Thomas Hellström wrote:
> Hi, Adrian
> 
> On 1/21/22 23:22, Adrian Larumbe wrote:
> > When a flat-CCS lmem-bound BO is evicted onto smem for the first
> > time, a
> > separate swap gem object is created to hold the contents of the CCS
> > block.
> > It is assumed that, for a flat-CCS bo to be migrated back onto
> > lmem, it
> > should've begun its life in lmem.
> > 
> > It also handles destruction of the swap bo when the original TTM
> > object
> > reaches the end of its life.
> > 
> > Signed-off-by: Adrian Larumbe <adrian.larumbe at collabora.com>
> 
> 
> While allocating a separate object for the CCS data is certainly
> possible, it poses some additional difficulties that have not been
> addressed here.
> 
> The CCS object needs to share the dma_resv of the original object.
> That
> is because the CCS object needs to be locked and validated when we
> process it, and we
> can only trylock within the ttm move callback which might therefore
> fail
> and isn't sufficient on swapin. We'd need to create some
> i915_gem_object_create_region_locked() that wraps
> ttm_bo_init_reserved().

Actually that would be a function to create with a reservation object
shared from another object.

/Thomas