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[PATCH v2] dma-buf: Wait on the reservation object when sync'ing before CPU access

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  [PATCH v2] dma-buf: Wait on the reservation object when sync'ing before CPU access Chris Wilson <chris@chris-wilson.co.uk> - 2016-08-15 17:50 +0200
    Re: [PATCH v2] dma-buf: Wait on the reservation object when sync'ing  before CPU access Daniel Vetter <daniel@ffwll.ch> - 2016-08-15 18:10 +0200

#1462942 — [PATCH v2] dma-buf: Wait on the reservation object when sync'ing before CPU access

Rendering operations to the dma-buf are tracked implicitly via the
reservation_object (dmabuf->resv). This is used to allow poll() to
wait upon outstanding rendering (or just query the current status of
rendering). The dma-buf sync ioctl allows userspace to prepare the
dma-buf for CPU access, which should include waiting upon rendering.
(Some drivers may need to do more work to ensure that the dma-buf mmap
is coherent as well as complete.)

v2: Always wait upon the reservation object implicitly. We choose to do
it after the native handler in case it can do so more efficiently.

Testcase: igt/prime_vgem
Testcase: igt/gem_concurrent_blit # *vgem*
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Eric Anholt <eric@anholt.net>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linaro-mm-sig@lists.linaro.org
Cc: linux-kernel@vger.kernel.org
---
 drivers/dma-buf/dma-buf.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index ddaee60ae52a..cf04d249a6a4 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -586,6 +586,22 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
 }
 EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
 
+static int __dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
+				      enum dma_data_direction direction)
+{
+	bool write = (direction == DMA_BIDIRECTIONAL ||
+		      direction == DMA_TO_DEVICE);
+	struct reservation_object *resv = dmabuf->resv;
+	long ret;
+
+	/* Wait on any implicit rendering fences */
+	ret = reservation_object_wait_timeout_rcu(resv, write, true,
+						  MAX_SCHEDULE_TIMEOUT);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
 
 /**
  * dma_buf_begin_cpu_access - Must be called before accessing a dma_buf from the
@@ -608,6 +624,13 @@ int dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
 	if (dmabuf->ops->begin_cpu_access)
 		ret = dmabuf->ops->begin_cpu_access(dmabuf, direction);
 
+	/* Ensure that all fences are waited upon - but we first allow
+	 * the native handler the chance to do so more efficiently if it
+	 * chooses. A double invocation here will be reasonably cheap no-op.
+	 */
+	if (ret == 0)
+		ret = __dma_buf_begin_cpu_access(dmabuf, direction);
+
 	return ret;
 }
 EXPORT_SYMBOL_GPL(dma_buf_begin_cpu_access);
-- 
2.8.1

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#1462959 — Re: [PATCH v2] dma-buf: Wait on the reservation object when sync'ing before CPU access

On Mon, Aug 15, 2016 at 04:42:18PM +0100, Chris Wilson wrote:
> Rendering operations to the dma-buf are tracked implicitly via the
> reservation_object (dmabuf->resv). This is used to allow poll() to
> wait upon outstanding rendering (or just query the current status of
> rendering). The dma-buf sync ioctl allows userspace to prepare the
> dma-buf for CPU access, which should include waiting upon rendering.
> (Some drivers may need to do more work to ensure that the dma-buf mmap
> is coherent as well as complete.)
> 
> v2: Always wait upon the reservation object implicitly. We choose to do
> it after the native handler in case it can do so more efficiently.
> 
> Testcase: igt/prime_vgem
> Testcase: igt/gem_concurrent_blit # *vgem*
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Sumit Semwal <sumit.semwal@linaro.org>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Eric Anholt <eric@anholt.net>
> Cc: linux-media@vger.kernel.org
> Cc: dri-devel@lists.freedesktop.org
> Cc: linaro-mm-sig@lists.linaro.org
> Cc: linux-kernel@vger.kernel.org
> ---
>  drivers/dma-buf/dma-buf.c | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index ddaee60ae52a..cf04d249a6a4 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -586,6 +586,22 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
>  }
>  EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
>  
> +static int __dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
> +				      enum dma_data_direction direction)
> +{
> +	bool write = (direction == DMA_BIDIRECTIONAL ||
> +		      direction == DMA_TO_DEVICE);
> +	struct reservation_object *resv = dmabuf->resv;
> +	long ret;
> +
> +	/* Wait on any implicit rendering fences */
> +	ret = reservation_object_wait_timeout_rcu(resv, write, true,
> +						  MAX_SCHEDULE_TIMEOUT);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
>  
>  /**
>   * dma_buf_begin_cpu_access - Must be called before accessing a dma_buf from the
> @@ -608,6 +624,13 @@ int dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
>  	if (dmabuf->ops->begin_cpu_access)
>  		ret = dmabuf->ops->begin_cpu_access(dmabuf, direction);
>  
> +	/* Ensure that all fences are waited upon - but we first allow
> +	 * the native handler the chance to do so more efficiently if it
> +	 * chooses. A double invocation here will be reasonably cheap no-op.
> +	 */
> +	if (ret == 0)
> +		ret = __dma_buf_begin_cpu_access(dmabuf, direction);

Not sure we should wait first and the flush or the other way round. But I
don't think it'll matter for any current dma-buf exporter, so meh.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Sumits, can you pls pick this one up and put into drm-misc?
-Daniel

> +
>  	return ret;
>  }
>  EXPORT_SYMBOL_GPL(dma_buf_begin_cpu_access);
> -- 
> 2.8.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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