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

From: Sean Paul
Date: Fri Feb 23 2018 - 11:14:18 EST

On Fri, Feb 23, 2018 at 08:17:52AM -0500, Rob Clark wrote:
> From: Brian Starkey <brian.starkey@xxxxxxx>
>
> 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@xxxxxxx>
> [rebased and fixed conflicts]
> Signed-off-by: Mihail Atanassov <mihail.atanassov@xxxxxxx>
> Signed-off-by: Liviu Dudau <liviu.dudau@xxxxxxx>
> Signed-off-by: Rob Clark <robdclark@xxxxxxxxx>

Reviewed-by: Sean Paul <seanpaul@xxxxxxxxxxxx>

> ---
> 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