drm/i915: Skip CPU synchronisation on dmabuf attachments (cbc1f3cb) · Commits · 戴 / test

dma-bufs are device coherent, with explicit CPU synchronisation provided via the begin/end cpu access ioctls. As the coherency of the dma-buf is explicitly defined to be under user control, flushing any caches on attach/detach of the dma-buf is additional work that doesn't aide the user in the slightest. Suggested-by:

Lucas Stach <l.stach@pengutronix.de> Signed-off-by:

Chris Wilson <chris@chris-wilson.co.uk> Acked-by:

Dongwon Kim <dongwon.kim@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20171130180702.29357-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -48,7 +48,9 @@ static struct sg_table i915_gem_map_dma_buf(struct dma_buf_attachment attachme
		src = sg_next(src);
		}

		if (!dma_map_sg(attachment->dev, st->sgl, st->nents, dir)) {
		if (!dma_map_sg_attrs(attachment->dev,
		st->sgl, st->nents, dir,
		DMA_ATTR_SKIP_CPU_SYNC)) {
		ret = -ENOMEM;
		goto err_free_sg;
		}
		@@ -71,7 +73,9 @@ static void i915_gem_unmap_dma_buf(struct dma_buf_attachment *attachment,
		{
		struct drm_i915_gem_object *obj = dma_buf_to_obj(attachment->dmabuf);

		dma_unmap_sg(attachment->dev, sg->sgl, sg->nents, dir);
		dma_unmap_sg_attrs(attachment->dev,
		sg->sgl, sg->nents, dir,
		DMA_ATTR_SKIP_CPU_SYNC);
		sg_free_table(sg);
		kfree(sg);

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