Re: [RFC 2/4] drm: writeback: Add out-fences for writeback connectors

[Sean Paul <seanpaul-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>]

On Fri, Feb 23, 2018 at 08:17:52AM -0500, Rob Clark wrote:
> From: Brian Starkey <brian.starkey@arm.com>
> 
> Add the WRITEBACK_OUT_FENCE_PTR property to writeback connectors, to
> enable userspace to get a fence which will signal once the writeback is
> complete. It is not allowed to request an out-fence without a
> framebuffer attached to the connector.
> 
> A timeline is added to drm_writeback_connector for use by the writeback
> out-fences.
> 
> In the case of a commit failure or DRM_MODE_ATOMIC_TEST_ONLY, the fence
> is set to -1.
> 
> Changes from v2:
>  - Rebase onto Gustavo Padovan's v9 explicit sync series
>  - Change out_fence_ptr type to s32 __user *
>  - Set *out_fence_ptr to -1 in drm_atomic_connector_set_property
>  - Store fence in drm_writeback_job
>  Gustavo Padovan:
>  - Move out_fence_ptr out of connector_state
>  - Signal fence from drm_writeback_signal_completion instead of
>    in driver directly
> 
> Changes from v3:
>  - Rebase onto 7e9081c5aac7 drm/fence: fix memory overwrite when setting out_fence fd
>    (change out_fence_ptr to s32 __user *, for real this time.)
>  - Update documentation around WRITEBACK_OUT_FENCE_PTR
> 
> Signed-off-by: Brian Starkey <brian.starkey@arm.com>
> [rebased and fixed conflicts]
> Signed-off-by: Mihail Atanassov <mihail.atanassov@arm.com>
> Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
> Signed-off-by: Rob Clark <robdclark@gmail.com>

Reviewed-by: Sean Paul <seanpaul@chromium.org>

> ---
>  drivers/gpu/drm/drm_atomic.c    |  99 ++++++++++++++++++++++++++++++++----
>  drivers/gpu/drm/drm_writeback.c | 109 +++++++++++++++++++++++++++++++++++++++-
>  include/drm/drm_atomic.h        |   8 +++
>  include/drm/drm_connector.h     |   8 +--
>  include/drm/drm_mode_config.h   |   8 +++
>  include/drm/drm_writeback.h     |  41 ++++++++++++++-
>  6 files changed, 257 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 019f131fe8be..fc8c4da409ff 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -318,6 +318,35 @@ static s32 __user *get_out_fence_for_crtc(struct drm_atomic_state *state,
>  	return fence_ptr;
>  }
>  
> +static int set_out_fence_for_connector(struct drm_atomic_state *state,
> +					struct drm_connector *connector,
> +					s32 __user *fence_ptr)
> +{
> +	unsigned int index = drm_connector_index(connector);
> +
> +	if (!fence_ptr)
> +		return 0;
> +
> +	if (put_user(-1, fence_ptr))
> +		return -EFAULT;
> +
> +	state->connectors[index].out_fence_ptr = fence_ptr;
> +
> +	return 0;
> +}
> +
> +static s32 __user *get_out_fence_for_connector(struct drm_atomic_state *state,
> +					       struct drm_connector *connector)
> +{
> +	unsigned int index = drm_connector_index(connector);
> +	s32 __user *fence_ptr;
> +
> +	fence_ptr = state->connectors[index].out_fence_ptr;
> +	state->connectors[index].out_fence_ptr = NULL;
> +
> +	return fence_ptr;
> +}
> +
>  /**
>   * drm_atomic_set_mode_for_crtc - set mode for CRTC
>   * @state: the CRTC whose incoming state to update
> @@ -676,6 +705,12 @@ static int drm_atomic_connector_check(struct drm_connector *connector,
>  		return -EINVAL;
>  	}
>  
> +	if (writeback_job->out_fence && !writeback_job->fb) {
> +		DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] requesting out-fence without framebuffer\n",
> +				 connector->base.id, connector->name);
> +		return -EINVAL;
> +	}
> +
>  	return 0;
>  }
>  
> @@ -1277,6 +1312,11 @@ static int drm_atomic_connector_set_property(struct drm_connector *connector,
>  		if (fb)
>  			drm_framebuffer_unreference(fb);
>  		return ret;
> +	} else if (property == config->writeback_out_fence_ptr_property) {
> +		s32 __user *fence_ptr = u64_to_user_ptr(val);
> +
> +		return set_out_fence_for_connector(state->state, connector,
> +						   fence_ptr);
>  	} else if (connector->funcs->atomic_set_property) {
>  		return connector->funcs->atomic_set_property(connector,
>  				state, property, val);
> @@ -1361,6 +1401,8 @@ 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->writeback_out_fence_ptr_property) {
> +		*val = 0;
>  	} else if (connector->funcs->atomic_get_property) {
>  		return connector->funcs->atomic_get_property(connector,
>  				state, property, val);
> @@ -2221,7 +2263,7 @@ static int setup_out_fence(struct drm_out_fence_state *fence_state,
>  	return 0;
>  }
>  
> -static int prepare_crtc_signaling(struct drm_device *dev,
> +static int prepare_signaling(struct drm_device *dev,
>  				  struct drm_atomic_state *state,
>  				  struct drm_mode_atomic *arg,
>  				  struct drm_file *file_priv,
> @@ -2230,6 +2272,8 @@ static int prepare_crtc_signaling(struct drm_device *dev,
>  {
>  	struct drm_crtc *crtc;
>  	struct drm_crtc_state *crtc_state;
> +	struct drm_connector *conn;
> +	struct drm_connector_state *conn_state;
>  	int i, c = 0, ret;
>  
>  	if (arg->flags & DRM_MODE_ATOMIC_TEST_ONLY)
> @@ -2295,6 +2339,43 @@ static int prepare_crtc_signaling(struct drm_device *dev,
>  		c++;
>  	}
>  
> +	for_each_new_connector_in_state(state, conn, conn_state, i) {
> +		struct drm_writeback_job *job;
> +		struct drm_out_fence_state *f;
> +		struct dma_fence *fence;
> +		s32 __user *fence_ptr;
> +
> +		fence_ptr = get_out_fence_for_connector(state, conn);
> +		if (!fence_ptr)
> +			continue;
> +
> +		job = drm_atomic_get_writeback_job(conn_state);
> +		if (!job)
> +			return -ENOMEM;
> +
> +		f = krealloc(*fence_state, sizeof(**fence_state) *
> +			     (*num_fences + 1), GFP_KERNEL);
> +		if (!f)
> +			return -ENOMEM;
> +
> +		memset(&f[*num_fences], 0, sizeof(*f));
> +
> +		f[*num_fences].out_fence_ptr = fence_ptr;
> +		*fence_state = f;
> +
> +		fence = drm_writeback_get_out_fence((struct drm_writeback_connector *)conn);
> +		if (!fence)
> +			return -ENOMEM;
> +
> +		ret = setup_out_fence(&f[(*num_fences)++], fence);
> +		if (ret) {
> +			dma_fence_put(fence);
> +			return ret;
> +		}
> +
> +		job->out_fence = fence;
> +	}
> +
>  	/*
>  	 * Having this flag means user mode pends on event which will never
>  	 * reach due to lack of at least one CRTC for signaling
> @@ -2305,11 +2386,11 @@ static int prepare_crtc_signaling(struct drm_device *dev,
>  	return 0;
>  }
>  
> -static void complete_crtc_signaling(struct drm_device *dev,
> -				    struct drm_atomic_state *state,
> -				    struct drm_out_fence_state *fence_state,
> -				    unsigned int num_fences,
> -				    bool install_fds)
> +static void complete_signaling(struct drm_device *dev,
> +			       struct drm_atomic_state *state,
> +			       struct drm_out_fence_state *fence_state,
> +			       unsigned int num_fences,
> +			       bool install_fds)
>  {
>  	struct drm_crtc *crtc;
>  	struct drm_crtc_state *crtc_state;
> @@ -2488,8 +2569,8 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
>  		drm_mode_object_put(obj);
>  	}
>  
> -	ret = prepare_crtc_signaling(dev, state, arg, file_priv, &fence_state,
> -				     &num_fences);
> +	ret = prepare_signaling(dev, state, arg, file_priv, &fence_state,
> +				&num_fences);
>  	if (ret)
>  		goto out;
>  
> @@ -2507,7 +2588,7 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
>  out:
>  	drm_atomic_clean_old_fb(dev, plane_mask, ret);
>  
> -	complete_crtc_signaling(dev, state, fence_state, num_fences, !ret);
> +	complete_signaling(dev, state, fence_state, num_fences, !ret);
>  
>  	if (ret == -EDEADLK) {
>  		drm_atomic_state_clear(state);
> diff --git a/drivers/gpu/drm/drm_writeback.c b/drivers/gpu/drm/drm_writeback.c
> index da61f929cbc3..839e79932c19 100644
> --- a/drivers/gpu/drm/drm_writeback.c
> +++ b/drivers/gpu/drm/drm_writeback.c
> @@ -13,6 +13,7 @@
>  #include <drm/drm_property.h>
>  #include <drm/drm_writeback.h>
>  #include <drm/drmP.h>
> +#include <linux/dma-fence.h>
>  
>  /**
>   * DOC: overview
> @@ -30,6 +31,16 @@
>   * framebuffer applies only to a single commit (see below). A framebuffer may
>   * not be attached while the CRTC is off.
>   *
> + * 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
> + * WRITEBACK_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 some additional properties, which userspace
>   * can use to query and control them:
>   *
> @@ -46,8 +57,54 @@
>   *	data is an array of u32 DRM_FORMAT_* fourcc values.
>   *	Userspace can use this blob to find out what pixel formats are supported
>   *	by the connector's writeback engine.
> + *
> + *  "WRITEBACK_OUT_FENCE_PTR":
> + *	Userspace can use this property to provide a pointer for the kernel to
> + *	fill with a sync_file file descriptor, which will signal once the
> + *	writeback is finished. The value should be the address of a 32-bit
> + *	signed integer, cast to a u64.
> + *	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_wb_connector(x) container_of(x->lock, \
> +					      struct drm_writeback_connector, \
> +					      fence_lock)
> +
> +static const char *drm_writeback_fence_get_driver_name(struct dma_fence *fence)
> +{
> +	struct drm_writeback_connector *wb_connector =
> +		fence_to_wb_connector(fence);
> +
> +	return wb_connector->base.dev->driver->name;
> +}
> +
> +static const char *
> +drm_writeback_fence_get_timeline_name(struct dma_fence *fence)
> +{
> +	struct drm_writeback_connector *wb_connector =
> +		fence_to_wb_connector(fence);
> +
> +	return wb_connector->timeline_name;
> +}
> +
> +static bool drm_writeback_fence_enable_signaling(struct dma_fence *fence)
> +{
> +	return true;
> +}
> +
> +static const struct dma_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 = dma_fence_default_wait,
> +};
> +
>  static bool create_writeback_properties(struct drm_device *dev)
>  {
>  	struct drm_property *prop;
> @@ -69,6 +126,15 @@ static bool create_writeback_properties(struct drm_device *dev)
>  		dev->mode_config.writeback_pixel_formats_property = prop;
>  	}
>  
> +	if (!dev->mode_config.writeback_out_fence_ptr_property) {
> +		prop = drm_property_create_range(dev, DRM_MODE_PROP_ATOMIC,
> +						 "WRITEBACK_OUT_FENCE_PTR", 0,
> +						 U64_MAX);
> +		if (!prop)
> +			return -ENOMEM;
> +		dev->mode_config.writeback_out_fence_ptr_property = prop;
> +	}
> +
>  	return true;
>  }
>  
> @@ -138,6 +204,15 @@ int drm_writeback_connector_init(struct drm_device *dev,
>  	INIT_LIST_HEAD(&wb_connector->job_queue);
>  	spin_lock_init(&wb_connector->job_lock);
>  
> +	wb_connector->fence_context = dma_fence_context_alloc(1);
> +	spin_lock_init(&wb_connector->fence_lock);
> +	snprintf(wb_connector->timeline_name,
> +		 sizeof(wb_connector->timeline_name),
> +		 "CONNECTOR:%d-%s", connector->base.id, connector->name);
> +
> +	drm_object_attach_property(&connector->base,
> +				   config->writeback_out_fence_ptr_property, 0);
> +
>  	drm_object_attach_property(&connector->base,
>  				   config->writeback_fb_id_property, 0);
>  
> @@ -200,6 +275,7 @@ void drm_writeback_cleanup_job(struct drm_writeback_job *job)
>  
>  	if (job->fb)
>  		drm_framebuffer_unreference(job->fb);
> +	dma_fence_put(job->out_fence);
>  	kfree(job);
>  }
>  EXPORT_SYMBOL(drm_writeback_cleanup_job);
> @@ -222,6 +298,7 @@ static void cleanup_work(struct work_struct *work)
>  /**
>   * drm_writeback_signal_completion - Signal the completion of a writeback job
>   * @wb_connector: The writeback connector whose job is complete
> + * @status: Status code to set in the writeback out_fence (0 for success)
>   *
>   * Drivers should call this to signal the completion of a previously queued
>   * writeback job. It should be called as soon as possible after the hardware
> @@ -235,7 +312,8 @@ static void cleanup_work(struct work_struct *work)
>   * See also: drm_writeback_queue_job()
>   */
>  void
> -drm_writeback_signal_completion(struct drm_writeback_connector *wb_connector)
> +drm_writeback_signal_completion(struct drm_writeback_connector *wb_connector,
> +				int status)
>  {
>  	unsigned long flags;
>  	struct drm_writeback_job *job;
> @@ -244,8 +322,14 @@ drm_writeback_signal_completion(struct drm_writeback_connector *wb_connector)
>  	job = list_first_entry_or_null(&wb_connector->job_queue,
>  				       struct drm_writeback_job,
>  				       list_entry);
> -	if (job)
> +	if (job) {
>  		list_del(&job->list_entry);
> +		if (job->out_fence) {
> +			if (status)
> +				dma_fence_set_error(job->out_fence, status);
> +			dma_fence_signal(job->out_fence);
> +		}
> +	}
>  	spin_unlock_irqrestore(&wb_connector->job_lock, flags);
>  
>  	if (WARN_ON(!job))
> @@ -255,3 +339,24 @@ drm_writeback_signal_completion(struct drm_writeback_connector *wb_connector)
>  	queue_work(system_long_wq, &job->cleanup_work);
>  }
>  EXPORT_SYMBOL(drm_writeback_signal_completion);
> +
> +struct dma_fence *
> +drm_writeback_get_out_fence(struct drm_writeback_connector *wb_connector)
> +{
> +	struct dma_fence *fence;
> +
> +	if (WARN_ON(wb_connector->base.connector_type !=
> +		    DRM_MODE_CONNECTOR_WRITEBACK))
> +		return NULL;
> +
> +	fence = kzalloc(sizeof(*fence), GFP_KERNEL);
> +	if (!fence)
> +		return NULL;
> +
> +	dma_fence_init(fence, &drm_writeback_fence_ops,
> +		       &wb_connector->fence_lock, wb_connector->fence_context,
> +		       ++wb_connector->fence_seqno);
> +
> +	return fence;
> +}
> +EXPORT_SYMBOL(drm_writeback_get_out_fence);
> diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> index d7b0263cc5cf..09076a625637 100644
> --- a/include/drm/drm_atomic.h
> +++ b/include/drm/drm_atomic.h
> @@ -160,6 +160,14 @@ struct __drm_crtcs_state {
>  struct __drm_connnectors_state {
>  	struct drm_connector *ptr;
>  	struct drm_connector_state *state, *old_state, *new_state;
> +	/**
> +	 * @out_fence_ptr:
> +	 *
> +	 * User-provided pointer which the kernel uses to return a sync_file
> +	 * file descriptor. Used by writeback connectors to signal completion of
> +	 * the writeback.
> +	 */
> +	s32 __user *out_fence_ptr;
>  };
>  
>  struct drm_private_obj;
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index 8701ebcc68b3..da56fda6e218 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -429,10 +429,10 @@ struct drm_connector_state {
>  	/**
>  	 * @writeback_job: Writeback job for writeback connectors
>  	 *
> -	 * Holds the framebuffer for a writeback connector. As the writeback
> -	 * completion may be asynchronous to the normal commit cycle, the
> -	 * writeback job lifetime is managed separately from the normal atomic
> -	 * state by this object.
> +	 * Holds the framebuffer and out-fence for a writeback connector. As
> +	 * the writeback completion may be asynchronous to the normal commit
> +	 * cycle, the writeback job lifetime is managed separately from the
> +	 * normal atomic state by this object.
>  	 *
>  	 * See also: drm_writeback_queue_job() and
>  	 * drm_writeback_signal_completion()
> diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
> index c012e1148ec0..930e00560380 100644
> --- a/include/drm/drm_mode_config.h
> +++ b/include/drm/drm_mode_config.h
> @@ -792,6 +792,14 @@ struct drm_mode_config {
>  	 * See also: drm_writeback_connector_init()
>  	 */
>  	struct drm_property *writeback_pixel_formats_property;
> +	/**
> +	 * @writeback_out_fence_ptr_property: Property for writeback connectors,
> +	 * fd pointer representing the outgoing fences for a writeback
> +	 * connector. Userspace should provide a pointer to a value of type s32,
> +	 * and then cast that pointer to u64.
> +	 * See also: drm_writeback_connector_init()
> +	 */
> +	struct drm_property *writeback_out_fence_ptr_property;
>  
>  	/* dumb ioctl parameters */
>  	uint32_t preferred_depth, prefer_shadow;
> diff --git a/include/drm/drm_writeback.h b/include/drm/drm_writeback.h
> index 0bb95fd4907d..b9470ae2a53d 100644
> --- a/include/drm/drm_writeback.h
> +++ b/include/drm/drm_writeback.h
> @@ -49,6 +49,32 @@ struct drm_writeback_connector {
>  	 * drm_writeback_signal_completion()
>  	 */
>  	struct list_head job_queue;
> +
> +	/**
> +	 * @fence_context:
> +	 *
> +	 * timeline context used for fence operations.
> +	 */
> +	unsigned int fence_context;
> +	/**
> +	 * @fence_lock:
> +	 *
> +	 * spinlock to protect the fences in the fence_context.
> +	 */
> +	spinlock_t fence_lock;
> +	/**
> +	 * @fence_seqno:
> +	 *
> +	 * Seqno variable used as monotonic counter for the fences
> +	 * created on the connector's timeline.
> +	 */
> +	unsigned long fence_seqno;
> +	/**
> +	 * @timeline_name:
> +	 *
> +	 * The name of the connector's fence timeline.
> +	 */
> +	char timeline_name[32];
>  };
>  #define to_wb_connector(x) container_of(x, struct drm_writeback_connector, base)
>  
> @@ -73,6 +99,13 @@ struct drm_writeback_job {
>  	 * directly, use drm_atomic_set_writeback_fb_for_connector()
>  	 */
>  	struct drm_framebuffer *fb;
> +
> +	/**
> +	 * @out_fence:
> +	 *
> +	 * Fence which will signal once the writeback has completed
> +	 */
> +	struct dma_fence *out_fence;
>  };
>  
>  int drm_writeback_connector_init(struct drm_device *dev,
> @@ -85,5 +118,11 @@ void drm_writeback_queue_job(struct drm_writeback_connector *wb_connector,
>  			     struct drm_writeback_job *job);
>  
>  void drm_writeback_cleanup_job(struct drm_writeback_job *job);
> -void drm_writeback_signal_completion(struct drm_writeback_connector *wb_connector);
> +
> +void
> +drm_writeback_signal_completion(struct drm_writeback_connector *wb_connector,
> +				int status);
> +
> +struct dma_fence *
> +drm_writeback_get_out_fence(struct drm_writeback_connector *wb_connector);
>  #endif
> -- 
> 2.14.3
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS
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