On Tue, Nov 22, 2016 at 09:11:28AM +0900, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
>
> Document IN_FENCE_FD and OUT_FENCE_PTR properties.
>
> v2: incorporate comments from Daniel Vetter
>
> Signed-off-by: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
> ---
> Documentation/gpu/drm-kms.rst | 6 +++++
> drivers/gpu/drm/drm_atomic.c | 52 +++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 58 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..f548e68 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -1809,6 +1809,58 @@ 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 transfered 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.
> + *
> + * 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 cases and use a
> + * fence_array if a merged fence is received. Passing -1 here means no
> + * fences to wait on.
> + *
> + * If the Atomic Commit request has the DRM_MODE_ATOMIC_TEST_ONLY flag
> + * it will only check if the Sync File is a valid one.
> + *
> + * On the driver side the fence is stored on the @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.
> + *
> + * 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
I've done an s/async/nonblocking/ here for consistency, since async commit
== tearing commit (but it might still block), and applied the patch to
drm-misc.
Thanks a lot for typing this!
-Daniel
> + * and for the DRM event handling for existing userspace.
> + */
> +
> static struct dma_fence *get_crtc_fence(struct drm_crtc *crtc)
> {
> struct dma_fence *fence;
> --
> 2.5.5
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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