Re: [PATCH v5 1/4] drm/fence: add in-fences support

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Oct 20, 2016 at 12:50:02PM -0200, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> 
> There is now a new property called FENCE_FD attached to every plane
> state that receives the sync_file fd from userspace via the atomic commit
> IOCTL.
> 
> The fd is then translated to a fence (that may be a fence_collection
> subclass or just a normal fence) and then used by DRM to fence_wait() for
> all fences in the sync_file to signal. So it only commits when all
> framebuffers are ready to scanout.
> 
> v2: Comments by Daniel Vetter:
> 	- remove set state->fence = NULL in destroy phase
> 	- accept fence -1 as valid and just return 0
> 	- do not call fence_get() - sync_file_fences_get() already calls it
> 	- fence_put() if state->fence is already set, in case userspace
> 	set the property more than once.
> 
> v3: WARN_ON if fence is set but state has no FB
> 
> v4: Comment from Maarten Lankhorst
> 	- allow set fence with no related fb
> 
> v5: rename FENCE_FD to IN_FENCE_FD
> 
> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

Since you rename plane_state->fence to in_fence (why exactly?) this breaks
compilation for imx and msm. Also there's the question of which fence
should win, if there's both explicit and implicit fences. I think the best
way to solve that is by adding a helper to set the implicit fence, which
drivers are supposed to call. That helper only sets the fence if there's
not yet an explicit fence attached. New sequence would be:

- patch1: roll out that helper (e.g. drm_atomic_plane_state_set_fence or
  whatever) for all drivers using it.
- patch2 (this one here): add explicit fences and change the helper to
  cooporate correctly.

> ---
>  drivers/gpu/drm/Kconfig             |  1 +
>  drivers/gpu/drm/drm_atomic.c        | 14 ++++++++++++++
>  drivers/gpu/drm/drm_atomic_helper.c | 13 +++++++------
>  drivers/gpu/drm/drm_crtc.c          |  6 ++++++
>  drivers/gpu/drm/drm_plane.c         |  1 +
>  include/drm/drm_crtc.h              |  5 +++++
>  include/drm/drm_plane.h             |  4 ++--
>  7 files changed, 36 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 483059a..43cb33d 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -12,6 +12,7 @@ menuconfig DRM
>  	select I2C
>  	select I2C_ALGOBIT
>  	select DMA_SHARED_BUFFER
> +	select SYNC_FILE
>  	help
>  	  Kernel-level support for the Direct Rendering Infrastructure (DRI)
>  	  introduced in XFree86 4.0. If you say Y here, you need to select
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 5dd7054..b3284b2 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -30,6 +30,7 @@
>  #include <drm/drm_atomic.h>
>  #include <drm/drm_mode.h>
>  #include <drm/drm_plane_helper.h>
> +#include <linux/sync_file.h>
>  
>  #include "drm_crtc_internal.h"
>  
> @@ -686,6 +687,17 @@ int drm_atomic_plane_set_property(struct drm_plane *plane,
>  		drm_atomic_set_fb_for_plane(state, fb);
>  		if (fb)
>  			drm_framebuffer_unreference(fb);
> +	} else if (property == config->prop_in_fence_fd) {
> +		if (U642I64(val) == -1)
> +			return 0;
> +
> +		if (state->in_fence)
> +			fence_put(state->in_fence);
> +
> +		state->in_fence = sync_file_get_fence(val);
> +		if (!state->in_fence)
> +			return -EINVAL;
> +
>  	} else if (property == config->prop_crtc_id) {
>  		struct drm_crtc *crtc = drm_crtc_find(dev, val);
>  		return drm_atomic_set_crtc_for_plane(state, crtc);
> @@ -745,6 +757,8 @@ drm_atomic_plane_get_property(struct drm_plane *plane,
>  
>  	if (property == config->prop_fb_id) {
>  		*val = (state->fb) ? state->fb->base.id : 0;
> +	} else if (property == config->prop_in_fence_fd) {
> +		*val = -1;
>  	} else if (property == config->prop_crtc_id) {
>  		*val = (state->crtc) ? state->crtc->base.id : 0;
>  	} else if (property == config->prop_crtc_x) {
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 07b432f..73464b1 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1031,22 +1031,20 @@ int drm_atomic_helper_wait_for_fences(struct drm_device *dev,
>  		if (!pre_swap)
>  			plane_state = plane->state;
>  
> -		if (!plane_state->fence)
> +		if (!plane_state->in_fence)
>  			continue;
>  
> -		WARN_ON(!plane_state->fb);
> -
>  		/*
>  		 * If waiting for fences pre-swap (ie: nonblock), userspace can
>  		 * still interrupt the operation. Instead of blocking until the
>  		 * timer expires, make the wait interruptible.
>  		 */
> -		ret = fence_wait(plane_state->fence, pre_swap);
> +		ret = fence_wait(plane_state->in_fence, pre_swap);
>  		if (ret)
>  			return ret;
>  
> -		fence_put(plane_state->fence);
> -		plane_state->fence = NULL;
> +		fence_put(plane_state->in_fence);
> +		plane_state->in_fence = NULL;
>  	}
>  
>  	return 0;
> @@ -3114,6 +3112,9 @@ void __drm_atomic_helper_plane_destroy_state(struct drm_plane_state *state)
>  {
>  	if (state->fb)
>  		drm_framebuffer_unreference(state->fb);
> +
> +	if (state->in_fence)
> +		fence_put(state->in_fence);
>  }
>  EXPORT_SYMBOL(__drm_atomic_helper_plane_destroy_state);
>  
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index 60403bf..fcb6453 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -397,6 +397,12 @@ static int drm_mode_create_standard_properties(struct drm_device *dev)
>  		return -ENOMEM;
>  	dev->mode_config.prop_fb_id = prop;
>  
> +	prop = drm_property_create_signed_range(dev, DRM_MODE_PROP_ATOMIC,
> +			"IN_FENCE_FD", -1, INT_MAX);
> +	if (!prop)
> +		return -ENOMEM;
> +	dev->mode_config.prop_in_fence_fd = prop;
> +
>  	prop = drm_property_create_object(dev, DRM_MODE_PROP_ATOMIC,
>  			"CRTC_ID", DRM_MODE_OBJECT_CRTC);
>  	if (!prop)
> diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
> index 249c0ae..3957ef8 100644
> --- a/drivers/gpu/drm/drm_plane.c
> +++ b/drivers/gpu/drm/drm_plane.c
> @@ -137,6 +137,7 @@ int drm_universal_plane_init(struct drm_device *dev, struct drm_plane *plane,
>  
>  	if (drm_core_check_feature(dev, DRIVER_ATOMIC)) {
>  		drm_object_attach_property(&plane->base, config->prop_fb_id, 0);
> +		drm_object_attach_property(&plane->base, config->prop_in_fence_fd, -1);
>  		drm_object_attach_property(&plane->base, config->prop_crtc_id, 0);
>  		drm_object_attach_property(&plane->base, config->prop_crtc_x, 0);
>  		drm_object_attach_property(&plane->base, config->prop_crtc_y, 0);
> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> index 284c1b3..279132e 100644
> --- a/include/drm/drm_crtc.h
> +++ b/include/drm/drm_crtc.h
> @@ -1206,6 +1206,11 @@ struct drm_mode_config {
>  	 */
>  	struct drm_property *prop_fb_id;
>  	/**
> +	 * @prop_in_fence_fd: Sync File fd representing the incoming fences
> +	 * for a Plane.
> +	 */
> +	struct drm_property *prop_in_fence_fd;
> +	/**
>  	 * @prop_crtc_id: Default atomic plane property to specify the
>  	 * &drm_crtc.
>  	 */
> diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
> index 0235390..3cb9bf1 100644
> --- a/include/drm/drm_plane.h
> +++ b/include/drm/drm_plane.h
> @@ -34,7 +34,7 @@ struct drm_crtc;
>   * @plane: backpointer to the plane
>   * @crtc: currently bound CRTC, NULL if disabled
>   * @fb: currently bound framebuffer
> - * @fence: optional fence to wait for before scanning out @fb
> + * @in_fence: optional fence to wait for before scanning out @fb
>   * @crtc_x: left position of visible portion of plane on crtc
>   * @crtc_y: upper position of visible portion of plane on crtc
>   * @crtc_w: width of visible portion of plane on crtc
> @@ -59,7 +59,7 @@ struct drm_plane_state {
>  
>  	struct drm_crtc *crtc;   /* do not write directly, use drm_atomic_set_crtc_for_plane() */
>  	struct drm_framebuffer *fb;  /* do not write directly, use drm_atomic_set_fb_for_plane() */
> -	struct fence *fence;
> +	struct fence *in_fence;

I think it'd be good to move the kerneldoc into an in-line comment here
and expand a bit upon the expected semantics. This is a pretty important
part of the atomic uabi!

Otherwise looks all good.
-Daniel

>  
>  	/* Signed dest location allows it to be partially off screen */
>  	int32_t crtc_x, crtc_y;
> -- 
> 2.5.5
> 

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