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

From: Brian Starkey
Date: Wed Oct 26 2016 - 08:46:34 EST

Hi Gustavo,

It would be great if you could cast your eye over this one as-well.
My intention was to be as similar to the CRTC out-fences as possible.

Thanks,
Brian

On Wed, Oct 26, 2016 at 09:55:07AM +0100, Brian Starkey wrote:
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@xxxxxxx>
---
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);
} 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;
+
+ 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