Re: [RFC PATCH v2 8/9] drm: writeback: Add out-fences for writeback connectors

[Gustavo Padovan <gustavo@padovan.org>]

2016-10-26 Brian Starkey <brian.starkey@arm.com>:

> Add the OUT_FENCE_PTR property to writeback connectors, to enable
> userspace to get a fence which will signal once the writeback is
> complete.
> 
> A timeline is added to drm_connector for use by the writeback
> out-fences. It is up to drivers to check for a fence in the
> connector_state and signal the it appropriately when their writeback has
> finished.
> 
> It is not allowed to request an out-fence without a framebuffer attached
> to the connector.
> 
> Signed-off-by: Brian Starkey <brian.starkey@arm.com>
> ---
>  drivers/gpu/drm/drm_atomic.c        |   60 +++++++++++++++++++++++---
>  drivers/gpu/drm/drm_atomic_helper.c |    5 ++-
>  drivers/gpu/drm/drm_writeback.c     |   80 +++++++++++++++++++++++++++++++++++
>  include/drm/drm_connector.h         |   14 ++++++
>  include/drm/drm_writeback.h         |    2 +
>  5 files changed, 155 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 3f8fc97..061ea13 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 <drm/drm_writeback.h>
>  #include <linux/sync_file.h>
>  
>  #include "drm_crtc_internal.h"
> @@ -646,6 +647,12 @@ static int drm_atomic_connector_check(struct drm_connector *connector,
>  		return -EINVAL;
>  	}
>  
> +	if (state->out_fence && !state->fb) {
> +		DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] requesting out-fence without framebuffer\n",
> +				 connector->base.id, connector->name);
> +		return -EINVAL;
> +	}
> +
>  	return 0;
>  }
>  
> @@ -1047,6 +1054,8 @@ int drm_atomic_connector_set_property(struct drm_connector *connector,
>  		drm_atomic_set_fb_for_connector(state, fb);
>  		if (fb)
>  			drm_framebuffer_unreference(fb);
> +	} else if (property == config->prop_out_fence_ptr) {
> +		state->out_fence_ptr = u64_to_user_ptr(val);

We need to move this out of the conn_state. For my v6 on CRTC out fences
I added drm_atomic_set_out_fence_for_crtc() and
drm_atomic_get_out_fence_for_crtc(). See padovan/fences.

>  	} else if (connector->funcs->atomic_set_property) {
>  		return connector->funcs->atomic_set_property(connector,
>  				state, property, val);
> @@ -1088,6 +1097,8 @@ drm_atomic_connector_get_property(struct drm_connector *connector,
>  	} else if (property == config->writeback_fb_id_property) {
>  		/* Writeback framebuffer is one-shot, write and forget */
>  		*val = 0;
> +	} else if (property == config->prop_out_fence_ptr) {
> +		*val = 0;
>  	} else if (connector->funcs->atomic_get_property) {
>  		return connector->funcs->atomic_get_property(connector,
>  				state, property, val);
> @@ -1736,6 +1747,39 @@ static int setup_out_fence(struct drm_out_fence_state *fence_state,
>  	return 0;
>  }
>  
> +static int setup_connector_out_fences(struct drm_atomic_state *state,
> +				      struct drm_out_fence_state *fence_state,
> +				      int *fence_idx)
> +{
> +	struct drm_connector *conn;
> +	struct drm_connector_state *conn_state;
> +	int i, ret;
> +
> +	for_each_connector_in_state(state, conn, conn_state, i) {
> +		struct fence *fence;
> +
> +		if (!conn_state->out_fence_ptr)
> +			continue;
> +
> +		fence = drm_writeback_get_out_fence(conn, conn_state);
> +		if (!fence)
> +			return -ENOMEM;
> +
> +		ret = setup_out_fence(&fence_state[(*fence_idx)++],
> +				      conn_state->out_fence_ptr,
> +				      fence);
> +		if (ret) {
> +			fence_put(fence);
> +			return ret;
> +		}
> +
> +		/* One-time usage only */
> +		conn_state->out_fence_ptr = NULL;
> +	}
> +
> +	return 0;
> +}
> +
>  int drm_mode_atomic_ioctl(struct drm_device *dev,
>  			  void *data, struct drm_file *file_priv)
>  {
> @@ -1868,8 +1912,8 @@ retry:
>  		drm_mode_object_unreference(obj);
>  	}
>  
> -	fence_state = kcalloc(dev->mode_config.num_crtc, sizeof(*fence_state),
> -			      GFP_KERNEL);
> +	fence_state = kcalloc(dev->mode_config.num_crtc + state->num_connector,
> +			      sizeof(*fence_state), GFP_KERNEL);
>  	if (!fence_state) {
>  		ret = -ENOMEM;
>  		goto out;
> @@ -1929,10 +1973,16 @@ retry:
>  		 * Below we call drm_atomic_state_free for it.
>  		 */
>  		ret = drm_atomic_check_only(state);
> -	} else if (arg->flags & DRM_MODE_ATOMIC_NONBLOCK) {
> -		ret = drm_atomic_nonblocking_commit(state);
>  	} else {
> -		ret = drm_atomic_commit(state);
> +		ret = setup_connector_out_fences(state, fence_state,
> +						 &fence_idx);
> +		if (ret)
> +			goto out;

I'd do this before this block. At the DRM_MODE_ATOMIC_TEST_ONLY or we
check or we commit. Moreover you should check if out_fences
are not set with TEST_ONLY.

> +
> +		if (arg->flags & DRM_MODE_ATOMIC_NONBLOCK)
> +			ret = drm_atomic_nonblocking_commit(state);
> +		else
> +			ret = drm_atomic_commit(state);
>  	}
>  
>  	if (!ret)
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index bba8672..88da299 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -3234,8 +3234,9 @@ __drm_atomic_helper_connector_duplicate_state(struct drm_connector *connector,
>  	if (state->crtc)
>  		drm_connector_reference(connector);
>  
> -	/* Don't copy over framebuffers, they are used only once */
> +	/* Don't copy over framebuffers or fences, they are used only once */
>  	state->fb = NULL;
> +	state->out_fence = NULL;
>  }
>  EXPORT_SYMBOL(__drm_atomic_helper_connector_duplicate_state);
>  
> @@ -3365,6 +3366,8 @@ __drm_atomic_helper_connector_destroy_state(struct drm_connector_state *state)
>  		drm_connector_unreference(state->connector);
>  	if (state->fb)
>  		drm_framebuffer_unreference(state->fb);
> +
> +	fence_put(state->out_fence);
>  }
>  EXPORT_SYMBOL(__drm_atomic_helper_connector_destroy_state);
>  
> diff --git a/drivers/gpu/drm/drm_writeback.c b/drivers/gpu/drm/drm_writeback.c
> index 5a6e0ad..4a6ef30 100644
> --- a/drivers/gpu/drm/drm_writeback.c
> +++ b/drivers/gpu/drm/drm_writeback.c
> @@ -11,6 +11,7 @@
>  #include <drm/drm_crtc.h>
>  #include <drm/drm_property.h>
>  #include <drm/drmP.h>
> +#include <linux/fence.h>
>  
>  /**
>   * DOC: overview
> @@ -32,6 +33,16 @@
>   * explicitly cleared in order to make a subsequent commit which doesn't use
>   * writeback.
>   *
> + * Unlike with planes, when a writeback framebuffer is removed by userspace DRM
> + * makes no attempt to remove it from active use by the connector. This is
> + * because no method is provided to abort a writeback operation, and in any
> + * case making a new commit whilst a writeback is ongoing is undefined (see
> + * OUT_FENCE_PTR below). As soon as the current writeback is finished, the
> + * framebuffer will automatically no longer be in active use. As it will also
> + * have already been removed from the framebuffer list, there will be no way for
> + * any userspace application to retrieve a reference to it in the intervening
> + * period.
> + *
>   * Writeback connectors have several additional properties, which userspace
>   * can use to query and control them:
>   *
> @@ -52,8 +63,48 @@
>   *  "PIXEL_FORMATS_SIZE":
>   *	Immutable unsigned range property storing the number of entries in the
>   *	PIXEL_FORMATS array.
> + *
> + *  "OUT_FENCE_PTR":
> + *	Userspace can provide the address of a 64-bit integer in this property,
> + *	which will be filled with a sync_file file descriptor by the kernel.
> + *	The sync_file will signal when the associated writeback has finished.
> + *	Userspace should wait for this fence to signal before making another
> + *	commit affecting any of the same CRTCs, Planes or Connectors.
> + *	**Failure to do so will result in undefined behaviour.**
> + *	For this reason it is strongly recommended that all userspace
> + *	applications making use of writeback connectors *always* retrieve an
> + *	out-fence for the commit and use it appropriately.
> + *	From userspace, this property will always read as zero.
>   */
>  
> +#define fence_to_connector(x) container_of(x->lock, struct drm_connector, fence_lock)
> +
> +static const char *drm_writeback_fence_get_driver_name(struct fence *fence)
> +{
> +	struct drm_connector *connector = fence_to_connector(fence);
> +
> +	return connector->dev->driver->name;
> +}
> +
> +static const char *drm_writeback_fence_get_timeline_name(struct fence *fence)
> +{
> +	struct drm_connector *connector = fence_to_connector(fence);
> +
> +	return connector->timeline_name;
> +}
> +
> +static bool drm_writeback_fence_enable_signaling(struct fence *fence)
> +{
> +	return true;
> +}
> +
> +static const struct fence_ops drm_writeback_fence_ops = {
> +	.get_driver_name = drm_writeback_fence_get_driver_name,
> +	.get_timeline_name = drm_writeback_fence_get_timeline_name,
> +	.enable_signaling = drm_writeback_fence_enable_signaling,
> +	.wait = fence_default_wait,
> +};
> +
>  /**
>   * create_writeback_properties - Create writeback connector-specific properties
>   * @dev: DRM device
> @@ -136,6 +187,14 @@ int drm_writeback_connector_init(struct drm_device *dev,
>  	if (ret)
>  		goto fail;
>  
> +	connector->fence_context = fence_context_alloc(1);
> +	spin_lock_init(&connector->fence_lock);
> +	snprintf(connector->timeline_name, sizeof(connector->timeline_name),
> +		 "CONNECTOR:%d", connector->base.id);
> +
> +	drm_object_attach_property(&connector->base,
> +				   config->prop_out_fence_ptr, 0);
> +
>  	drm_object_attach_property(&connector->base,
>  				   config->writeback_fb_id_property, 0);
>  
> @@ -155,3 +214,24 @@ fail:
>  	return ret;
>  }
>  EXPORT_SYMBOL(drm_writeback_connector_init);
> +
> +struct fence *drm_writeback_get_out_fence(struct drm_connector *connector,
> +					  struct drm_connector_state *conn_state)
> +{
> +	struct fence *fence;
> +
> +	if (WARN_ON(connector->connector_type != DRM_MODE_CONNECTOR_WRITEBACK))
> +		return NULL;
> +
> +	fence = kzalloc(sizeof(*fence), GFP_KERNEL);
> +	if (!fence)
> +		return NULL;
> +
> +	fence_init(fence, &drm_writeback_fence_ops, &connector->fence_lock,
> +		   connector->fence_context, ++connector->fence_seqno);
> +
> +	conn_state->out_fence = fence_get(fence);
> +
> +	return fence;
> +}
> +EXPORT_SYMBOL(drm_writeback_get_out_fence);
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index a5e3778..7d40537 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -199,6 +199,7 @@ int drm_display_info_set_bus_formats(struct drm_display_info *info,
>   * @best_encoder: can be used by helpers and drivers to select the encoder
>   * @state: backpointer to global drm_atomic_state
>   * @fb: Writeback framebuffer, for DRM_MODE_CONNECTOR_WRITEBACK
> + * @out_fence: Fence which will clear when the framebuffer write has finished
>   */
>  struct drm_connector_state {
>  	struct drm_connector *connector;
> @@ -216,6 +217,9 @@ struct drm_connector_state {
>  	struct drm_atomic_state *state;
>  
>  	struct drm_framebuffer *fb;  /* do not write directly, use drm_atomic_set_fb_for_connector() */
> +
> +	struct fence *out_fence;
> +	u64 __user *out_fence_ptr;
>  };
>  
>  /**
> @@ -546,6 +550,10 @@ struct drm_cmdline_mode {
>   * @tile_v_loc: vertical location of this tile
>   * @tile_h_size: horizontal size of this tile.
>   * @tile_v_size: vertical size of this tile.
> + * @fence_context: context for fence signalling
> + * @fence_lock: fence lock for the fence context
> + * @fence_seqno: seqno variable to create fences
> + * @timeline_name: fence timeline name
>   *
>   * Each connector may be connected to one or more CRTCs, or may be clonable by
>   * another connector if they can share a CRTC.  Each connector also has a specific
> @@ -694,6 +702,12 @@ struct drm_connector {
>  	uint8_t num_h_tile, num_v_tile;
>  	uint8_t tile_h_loc, tile_v_loc;
>  	uint16_t tile_h_size, tile_v_size;
> +
> +	/* fence timelines info for DRM out-fences */
> +	unsigned int fence_context;
> +	spinlock_t fence_lock;
> +	unsigned long fence_seqno;
> +	char timeline_name[32];
>  };
>  
>  #define obj_to_connector(x) container_of(x, struct drm_connector, base)
> diff --git a/include/drm/drm_writeback.h b/include/drm/drm_writeback.h
> index afdc2742..01f33bc 100644
> --- a/include/drm/drm_writeback.h
> +++ b/include/drm/drm_writeback.h
> @@ -16,4 +16,6 @@ int drm_writeback_connector_init(struct drm_device *dev,
>  				 const struct drm_connector_funcs *funcs,
>  				 u32 *formats, int n_formats);
>  
> +struct fence *drm_writeback_get_out_fence(struct drm_connector *connector,
> +					  struct drm_connector_state *conn_state);
>  #endif
> -- 
> 1.7.9.5
> 
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