On Mon, Aug 10, 2015 at 09:16:46PM +0100, Chris Wilson wrote: > If the set of pages is being imported from another device, we cannot > assume that it is fully coherent with the CPU cache, so mark it as such. > However, if the source is the shared memory vgem allocator, we could > treat the buffer as being cached (so long as all parties agree in the > case the same buffer is shared between multiple devices) but as of > today, vgem cannot export dma-bufs. > > Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk> > Cc: Daniel Vetter <daniel.vet...@ffwll.ch>
Yay for x86 dma api to refuse acknowleding that incoherent devices exist (since this should be done in the dma-ap/sg stuff imo for dma-bufs). But since x86 assumes that everything is coherent shouldn't we do the inverse and use snooping/cacheable always? That should be correct for everything modern at least, and for old agp crap (do we care even, is sharing possible there?) snooping should only result in a bit more overhead. Or where exactly does this blow up? -Daniel > --- > drivers/gpu/drm/i915/i915_gem_dmabuf.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/drivers/gpu/drm/i915/i915_gem_dmabuf.c > b/drivers/gpu/drm/i915/i915_gem_dmabuf.c > index 7748d57adffd..da5e4fb02350 100644 > --- a/drivers/gpu/drm/i915/i915_gem_dmabuf.c > +++ b/drivers/gpu/drm/i915/i915_gem_dmabuf.c > @@ -265,8 +265,22 @@ struct drm_gem_object *i915_gem_prime_import(struct > drm_device *dev, > i915_gem_object_init(obj, &i915_gem_object_dmabuf_ops); > obj->base.import_attach = attach; > > + /* This bo is imported from a foreign HW device with which we cannot > + * assume any coherency. Note that if this dma-buf was imported from > + * a simple page allocator, like vgem, then we could treat this as > + * cacheable (so long as all parties agree on that convention - i.e. > + * if the same bo was shared with nouveau/radeon they also treat it > + * as CPU cacheeable so that coherency is maintained between all > + * parties). > + */ > + ret = i915_gem_object_set_cache_level(obj, I915_CACHE_NONE); > + if (ret) > + goto fail_obj; > + > return &obj->base; > > +fail_obj: > + drm_gem_object_unreference(&obj->base); > fail_detach: > dma_buf_detach(dma_buf, attach); > dma_buf_put(dma_buf); > -- > 2.5.0 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/intel-gfx
