drm/prime: skip CPU sync in map/unmap dma_buf

Dma-bufs should already be device coherent, as they are only pulled in the
CPU domain via the begin/end cpu_access calls. As we cache the mapping set
up by dma_map_sg a CPU sync at this point will not actually guarantee proper
coherency on non-coherent architectures, so we can as well stop pretending.

This is an important performance fix for architectures which need explicit
cache synchronization and userspace doing lots of dma-buf imports.
Improves Weston on Etnaviv performance 5x, where before this patch > 90%
of Weston CPU time was spent synchronizing caches for buffers which are
already device coherent.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20171130173428.8666-1-l.stach@pengutronix.de

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 8de93a2..9a17725 100644 (file)
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -218,8 +218,9 @@ static void drm_gem_map_detach(struct dma_buf *dma_buf,
        sgt = prime_attach->sgt;
        if (sgt) {
                if (prime_attach->dir != DMA_NONE)
-                       dma_unmap_sg(attach->dev, sgt->sgl, sgt->nents,
-                                       prime_attach->dir);
+                       dma_unmap_sg_attrs(attach->dev, sgt->sgl, sgt->nents,
+                                          prime_attach->dir,
+                                          DMA_ATTR_SKIP_CPU_SYNC);
                sg_free_table(sgt);
        }
 
@@ -277,7 +278,8 @@ static struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
        sgt = obj->dev->driver->gem_prime_get_sg_table(obj);
 
        if (!IS_ERR(sgt)) {
-               if (!dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir)) {
+               if (!dma_map_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir,
+                                     DMA_ATTR_SKIP_CPU_SYNC)) {
                        sg_free_table(sgt);
                        kfree(sgt);
                        sgt = ERR_PTR(-ENOMEM);