Patchwork drm/fences: add DOC: for explicit fencing

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Submitter Gustavo F. Padovan
Date Nov. 21, 2016, 3:48 a.m.
Message ID <1479700093-4034-1-git-send-email-gustavo@padovan.org>
Download mbox | patch
Permalink /patch/9438695/
State New
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Comments

Gustavo F. Padovan - Nov. 21, 2016, 3:48 a.m.
From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

Document IN_FENCE_FD and OUT_FENCE_PTR properties.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
---
 Documentation/gpu/drm-kms.rst |  6 ++++++
 drivers/gpu/drm/drm_atomic.c  | 31 +++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)
Daniel Vetter - Nov. 21, 2016, 9:56 a.m.
On Mon, Nov 21, 2016 at 12:48:13PM +0900, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> 
> Document IN_FENCE_FD and OUT_FENCE_PTR properties.
> 
> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> ---
>  Documentation/gpu/drm-kms.rst |  6 ++++++
>  drivers/gpu/drm/drm_atomic.c  | 31 +++++++++++++++++++++++++++++++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst
> index 568f3c2..cdc9539 100644
> --- a/Documentation/gpu/drm-kms.rst
> +++ b/Documentation/gpu/drm-kms.rst
> @@ -287,6 +287,12 @@ Tile Group Property
>  .. kernel-doc:: drivers/gpu/drm/drm_connector.c
>     :doc: Tile group
>  
> +Explicit Fencing Properties
> +---------------------------
> +
> +.. kernel-doc:: drivers/gpu/drm/drm_atomic.c
> +   :doc: explicit fencing properties
> +
>  Existing KMS Properties
>  -----------------------
>  
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index b476ec5..7f33031 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -1809,6 +1809,37 @@ void drm_atomic_clean_old_fb(struct drm_device *dev,
>  }
>  EXPORT_SYMBOL(drm_atomic_clean_old_fb);
>  
> +/**
> + * DOC: explicit fencing properties
> + *
> + * Explicit fencing allows userspace to control the buffer synchronization
> + * between devices. A Fence or a group of fences are trasnfered to/from

s/trasn/trans/

> + * userspace using Sync File fds and there are two DRM properties for that.
> + * IN_FENCE_FD on each DRM Plane to send fences to the kernel and
> + * OUT_FENCE_PTR on each DRM CRTC to receive fences from the kernel.

I think a bit about implicit vs. explicit fencing would be useful in a
separate paragraph:

"As a contrast, with implicit fencing the kernel keeps track of any
ongoing rendering, and automatically ensures that the atomic update waits
for any pending rendering to complete. For shared buffers represented with
a struct &dma_buf this is tracked in &reservation_object structures.
Implicit syncing is how Linux traditionally worked (e.g. DRI2/3 on X.org),
whereas explicit fencing is what Android wants."

> + *
> + * "IN_FENCE_FD”:
> + *	Use this property to pass a fence that DRM should wait on before
> + *	proceeding with the Atomic Commit request and show the framebuffer for
> + *	the plane on the screen. The fence can be either a normal fence or a
> + *	merged one, the sync_file framework will handle both case and use a
s/case/cases/

> + *	fence_array if a merged fence is received. Passing -1 here means no
> + *	fences to wait on.

Please also document what the expecation is for a TEST_ONLY commit.

I think a line or so about the driver interface would be good here, e.g.

"On the driver side the fence is stored @fence parameter of struct
&drm_plane_state. Drivers which also support implicit fencing should set
the implicit fence using drm_atomic_set_fence_for_plane(), to make sure
there's consistent behaviour between drivers in precedence of implicit vs.
explicit fencing."

> + *
> + * "OUT_FENCE_PTR”:
> + *	Use this property to pass a file descriptor pointer to DRM. Once the
> + *	Atomic Commit request call returns OUT_FENCE_PTR will be filled with
> + *	the file descriptor number of a Sync File. This Sync File contains the
> + *	CRTC fence that will be signaled when all framebuffers present on the
> + *	Atomic Commit * request for that given CRTC are scanned out on the
> + *	screen.
> + *
> + *	The Atomic Commit request fails if a invalid pointer is passed. If the
> + *	Atomic Commit request fails for any other reason the out fence fd
> + *	returned will be -1. On a Atomic Commit with the
> + *	DRM_MODE_ATOMIC_TEST_ONLY flag the out fence will also be set to -1.

Same here about driver interface:

"Note that out-fences don't have a special interface to drivers and are
internally represented by a struct &drm_pending_vblank_event in struct
&drm_crtc_state, which is also used by the async atomic commit helpers and
for the DRM event handling for existing userspace."

Cheers, Daniel

> + */
> +
>  static struct dma_fence *get_crtc_fence(struct drm_crtc *crtc)
>  {
>  	struct dma_fence *fence;
> -- 
> 2.5.5
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

Patch

diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst
index 568f3c2..cdc9539 100644
--- a/Documentation/gpu/drm-kms.rst
+++ b/Documentation/gpu/drm-kms.rst
@@ -287,6 +287,12 @@  Tile Group Property
 .. kernel-doc:: drivers/gpu/drm/drm_connector.c
    :doc: Tile group
 
+Explicit Fencing Properties
+---------------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_atomic.c
+   :doc: explicit fencing properties
+
 Existing KMS Properties
 -----------------------
 
diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index b476ec5..7f33031 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -1809,6 +1809,37 @@  void drm_atomic_clean_old_fb(struct drm_device *dev,
 }
 EXPORT_SYMBOL(drm_atomic_clean_old_fb);
 
+/**
+ * DOC: explicit fencing properties
+ *
+ * Explicit fencing allows userspace to control the buffer synchronization
+ * between devices. A Fence or a group of fences are trasnfered to/from
+ * userspace using Sync File fds and there are two DRM properties for that.
+ * IN_FENCE_FD on each DRM Plane to send fences to the kernel and
+ * OUT_FENCE_PTR on each DRM CRTC to receive fences from the kernel.
+ *
+ * "IN_FENCE_FD”:
+ *	Use this property to pass a fence that DRM should wait on before
+ *	proceeding with the Atomic Commit request and show the framebuffer for
+ *	the plane on the screen. The fence can be either a normal fence or a
+ *	merged one, the sync_file framework will handle both case and use a
+ *	fence_array if a merged fence is received. Passing -1 here means no
+ *	fences to wait on.
+ *
+ * "OUT_FENCE_PTR”:
+ *	Use this property to pass a file descriptor pointer to DRM. Once the
+ *	Atomic Commit request call returns OUT_FENCE_PTR will be filled with
+ *	the file descriptor number of a Sync File. This Sync File contains the
+ *	CRTC fence that will be signaled when all framebuffers present on the
+ *	Atomic Commit * request for that given CRTC are scanned out on the
+ *	screen.
+ *
+ *	The Atomic Commit request fails if a invalid pointer is passed. If the
+ *	Atomic Commit request fails for any other reason the out fence fd
+ *	returned will be -1. On a Atomic Commit with the
+ *	DRM_MODE_ATOMIC_TEST_ONLY flag the out fence will also be set to -1.
+ */
+
 static struct dma_fence *get_crtc_fence(struct drm_crtc *crtc)
 {
 	struct dma_fence *fence;