[PATCH 1/3] drm: Wait on the reservation object when sync'ing dmabufs

[Chris Wilson]

Rendering operations to the dma-buf are tracked implicitly via the
reservation_object (dmabuf->resv). The dmabuf sync ioctl allows
userspace to wait upon outstanding rendering and prepare the object for
CPU access (provided by the prime dma_buf_ops.begin_cpu_access). Fill
this out for the generic drm_gem_prime by waiting on outstanding
rendering via dmabuf->resv. (This offers an alternative to using poll
that is consistent with other drivers that may need to more work to
prepare the object for access by the CPU.)

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/drm_prime.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 780589b420a4..479ff7cc3634 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -28,6 +28,7 @@
 
 #include <linux/export.h>
 #include <linux/dma-buf.h>
+#include <linux/reservation.h>
 #include <drm/drmP.h>
 #include <drm/drm_gem.h>
 
@@ -288,6 +289,22 @@ static int drm_gem_dmabuf_mmap(struct dma_buf *dma_buf,
 	return dev->driver->gem_prime_mmap(obj, vma);
 }
 
+static int drm_gem_begin_cpu_access(struct dma_buf *dma_buf,
+				    enum dma_data_direction direction)
+{
+	bool write = (direction == DMA_BIDIRECTIONAL ||
+		      direction == DMA_TO_DEVICE);
+	struct reservation_object *resv = dma_buf->resv;
+	long ret;
+
+	ret = reservation_object_wait_timeout_rcu(resv, write, true,
+						  MAX_SCHEDULE_TIMEOUT);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
 static const struct dma_buf_ops drm_gem_prime_dmabuf_ops =  {
 	.attach = drm_gem_map_attach,
 	.detach = drm_gem_map_detach,
@@ -301,6 +318,7 @@ static const struct dma_buf_ops drm_gem_prime_dmabuf_ops =  {
 	.mmap = drm_gem_dmabuf_mmap,
 	.vmap = drm_gem_dmabuf_vmap,
 	.vunmap = drm_gem_dmabuf_vunmap,
+	.begin_cpu_access = drm_gem_begin_cpu_access,
 };
 
 /**
-- 
2.8.1