Message-ID: <20161027100736.GB18708@e106950-lin.cambridge.arm.com>
Date:   Thu, 27 Oct 2016 11:07:37 +0100
From:   Brian Starkey <brian.starkey@....com>
To:     Gustavo Padovan <gustavo@...ovan.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org
Subject: Re: [RFC PATCH v2 8/9] drm: writeback: Add out-fences for writeback
 connectors

Hi Gustavo,

On Wed, Oct 26, 2016 at 07:40:29PM -0200, Gustavo Padovan wrote:
>2016-10-26 Brian Starkey <brian.starkey@....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@....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.
>

Yep, will do. I was expecting this to change

>>  	} 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.
>

I don't quite follow the second sentence; you mean you'd rather I
was finished setting things up before the TEST_ONLY check? That sounds
OK.

For TEST_ONLY I actually think we shouldn't reject commits with
OUT_FENCE_PTRs and TEST_ONLY. I thought the idea of TEST_ONLY was for
userspace to build a commit, then see if it can work, then commit it
for real.

By rejecting TEST_ONLY + OUT_FENCE_PTRs you're saying userspace can
never test what it actually intends to commit. It has to test, then
add the out-fences, then commit and hope for the best.

How about always setting the out-fences to -1 for TEST_ONLY?

Thanks for the review,
-Brian

>> +
>> +		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
>>
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@...ts.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>

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