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Subject[PATCH v7 2/3] drm: writeback: Add out-fences for writeback connectors
Date
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 commit 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>
---
drivers/gpu/drm/drm_atomic.c | 99 ++++++++++++++++++++++++++---
drivers/gpu/drm/drm_writeback.c | 108 +++++++++++++++++++++++++++++++-
include/drm/drm_atomic.h | 8 +++
include/drm/drm_connector.h | 8 +--
include/drm/drm_mode_config.h | 8 +++
include/drm/drm_writeback.h | 43 ++++++++++++-
6 files changed, 258 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 3f1e4b894803b..cc2f86c68b293 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
@@ -705,6 +734,12 @@ 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;
}

@@ -1320,6 +1355,11 @@ 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);
@@ -1404,6 +1444,8 @@ 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);
@@ -2263,7 +2305,7 @@ 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,
@@ -2272,6 +2314,8 @@ 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)
@@ -2337,6 +2381,43 @@ 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
@@ -2347,11 +2428,11 @@ 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;
@@ -2530,8 +2611,8 @@ 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;

@@ -2549,7 +2630,7 @@ 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 17cacd2170b0c..46a93a883344f 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 int create_writeback_properties(struct drm_device *dev)
{
struct drm_property *prop;
@@ -71,6 +128,15 @@ static int 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 0;
}

@@ -140,6 +206,15 @@ 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);

@@ -221,6 +296,7 @@ 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
@@ -234,7 +310,8 @@ 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;
@@ -243,8 +320,14 @@ 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))
@@ -254,3 +337,24 @@ 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 a5e904105db3a..7c77a1916182a 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 60c0ffb947d5e..b0d2ed13d625b 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -433,10 +433,10 @@ 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 de8881324f734..74fe26aaf5444 100644
--- a/include/drm/drm_mode_config.h
+++ b/include/drm/drm_mode_config.h
@@ -793,6 +793,14 @@ 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 cf3a28676006a..6a7462c1821ad 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];
};

struct drm_writeback_job {
@@ -59,12 +85,14 @@ struct drm_writeback_job {
* framebuffer reference to a workqueue.
*/
struct work_struct cleanup_work;
+
/**
* @list_entry:
*
* List item for the connector's @job_queue
*/
struct list_head list_entry;
+
/**
* @fb:
*
@@ -72,6 +100,13 @@ 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,
@@ -84,5 +119,11 @@ 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
--
2.17.0
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