[PATCH v2 1/5] media: mc: add manual request completion
Nicolas Dufresne
nicolas.dufresne at collabora.com
Thu Apr 10 11:41:36 PDT 2025
Hi Laurent,
Le jeudi 10 avril 2025 à 20:50 +0300, Laurent Pinchart a écrit :
> Hi Nicolas,
>
> Thank you for the patch.
>
> On Thu, Apr 10, 2025 at 11:39:56AM -0400, Nicolas Dufresne wrote:
> > From: Hans Verkuil <hverkuil at xs4all.nl>
> >
> > By default when the last request object is completed, the whole
> > request completes as well.
> >
> > But sometimes you want to manually complete a request in a driver,
> > so add a manual complete mode for this.
>
> I didn't immediately understand this was about delaying completion of
> the request. It would be nice to make that more explicit in the commit
> message and in the documentation of
> media_request_mark_manual_completion(). A sample use case would also
> help.
I have never considered this a "delay", but an explicit completion
function. In short you want to use that if you are not satisfied with
the existing implicit logic that currently delays and complete the
request based on the media_request_object attachments.
We can add this multi-core CODEC use case as an example.
The only alternative to that would have been to allocate a driver
specific media_request_object and store it in request. This is a rather
expensive and complicated way to do this. I even got to a point I
considered having a media_request_object in the driver specific
media_request, so avoid the runtime allocs, but found the explicit
completion a lot easier to read and think about.
My only remaining thought, is why do we keep the complicated explicit
completion in the first place, perhaps because its a lot of work to
undo ? The request_object still have a purpose, since we still need to
store data in the request. And it has some benefit, that instead of
silently never completing, the complete() call will warn if you have
left over objects at an unexpected point in time.
Nicolas
> > In req_queue the driver marks the request for manual completion by
> > calling media_request_mark_manual_completion, and when the driver
> > wants to manually complete the request it calls
> > media_request_manual_complete().
> >
> > Signed-off-by: Hans Verkuil <hverkuil-cisco at xs4all.nl>
> > Signed-off-by: Nicolas Dufresne <nicolas.dufresne at collabora.com>
> > ---
> > drivers/media/mc/mc-request.c | 38 ++++++++++++++++++++++++++++++++++++--
> > include/media/media-request.h | 36 +++++++++++++++++++++++++++++++++++-
> > 2 files changed, 71 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/media/mc/mc-request.c b/drivers/media/mc/mc-request.c
> > index 5edfc2791ce7c7485def5db675bbf53ee223d837..398d0806d1d274eb8c454fc5c37b77476abe1e74 100644
> > --- a/drivers/media/mc/mc-request.c
> > +++ b/drivers/media/mc/mc-request.c
> > @@ -54,6 +54,7 @@ static void media_request_clean(struct media_request *req)
> > req->access_count = 0;
> > WARN_ON(req->num_incomplete_objects);
> > req->num_incomplete_objects = 0;
> > + req->manual_completion = false;
> > wake_up_interruptible_all(&req->poll_wait);
> > }
> >
> > @@ -313,6 +314,7 @@ int media_request_alloc(struct media_device *mdev, int *alloc_fd)
> > req->mdev = mdev;
> > req->state = MEDIA_REQUEST_STATE_IDLE;
> > req->num_incomplete_objects = 0;
> > + req->manual_completion = false;
> > kref_init(&req->kref);
> > INIT_LIST_HEAD(&req->objects);
> > spin_lock_init(&req->lock);
> > @@ -459,7 +461,7 @@ void media_request_object_unbind(struct media_request_object *obj)
> >
> > req->num_incomplete_objects--;
> > if (req->state == MEDIA_REQUEST_STATE_QUEUED &&
> > - !req->num_incomplete_objects) {
> > + !req->num_incomplete_objects && !req->manual_completion) {
> > req->state = MEDIA_REQUEST_STATE_COMPLETE;
> > completed = true;
> > wake_up_interruptible_all(&req->poll_wait);
> > @@ -488,7 +490,7 @@ void media_request_object_complete(struct media_request_object *obj)
> > WARN_ON(req->state != MEDIA_REQUEST_STATE_QUEUED))
> > goto unlock;
> >
> > - if (!--req->num_incomplete_objects) {
> > + if (!--req->num_incomplete_objects && !req->manual_completion) {
> > req->state = MEDIA_REQUEST_STATE_COMPLETE;
> > wake_up_interruptible_all(&req->poll_wait);
> > completed = true;
> > @@ -499,3 +501,35 @@ void media_request_object_complete(struct media_request_object *obj)
> > media_request_put(req);
> > }
> > EXPORT_SYMBOL_GPL(media_request_object_complete);
> > +
> > +void media_request_manual_complete(struct media_request *req)
> > +{
> > + unsigned long flags;
> > + bool completed = false;
> > +
> > + if (WARN_ON(!req))
> > + return;
> > + if (WARN_ON(!req->manual_completion))
> > + return;
> > +
> > + spin_lock_irqsave(&req->lock, flags);
> > + if (WARN_ON(req->state != MEDIA_REQUEST_STATE_QUEUED))
> > + goto unlock;
> > +
> > + req->manual_completion = false;
> > + /*
> > + * It is expected that all other objects in this request are
> > + * completed when this function is called. WARN if that is
> > + * not the case.
> > + */
> > + if (!WARN_ON(req->num_incomplete_objects)) {
> > + req->state = MEDIA_REQUEST_STATE_COMPLETE;
> > + wake_up_interruptible_all(&req->poll_wait);
> > + completed = true;
> > + }
> > +unlock:
> > + spin_unlock_irqrestore(&req->lock, flags);
> > + if (completed)
> > + media_request_put(req);
> > +}
> > +EXPORT_SYMBOL_GPL(media_request_manual_complete);
> > diff --git a/include/media/media-request.h b/include/media/media-request.h
> > index d4ac557678a78372222704400c8c96cf3150b9d9..645d18907be7148ca50dcc9248ff06bd8ccdf953 100644
> > --- a/include/media/media-request.h
> > +++ b/include/media/media-request.h
> > @@ -56,6 +56,10 @@ struct media_request_object;
> > * @access_count: count the number of request accesses that are in progress
> > * @objects: List of @struct media_request_object request objects
> > * @num_incomplete_objects: The number of incomplete objects in the request
> > + * @manual_completion: if true, then the request won't be marked as completed
> > + * when @num_incomplete_objects reaches 0. Call media_request_manual_complete()
> > + * to set this field to false and complete the request
>
> I'd drop "set this field to false and " here.
>
> > + * if @num_incomplete_objects == 0.
>
> * after @num_incomplete_objects reaches 0.
>
> > * @poll_wait: Wait queue for poll
> > * @lock: Serializes access to this struct
> > */
> > @@ -68,6 +72,7 @@ struct media_request {
> > unsigned int access_count;
> > struct list_head objects;
> > unsigned int num_incomplete_objects;
> > + bool manual_completion;
> > wait_queue_head_t poll_wait;
> > spinlock_t lock;
> > };
> > @@ -218,6 +223,35 @@ media_request_get_by_fd(struct media_device *mdev, int request_fd);
> > int media_request_alloc(struct media_device *mdev,
> > int *alloc_fd);
> >
> > +/**
> > + * media_request_mark_manual_completion - Set manual_completion to true
> > + *
> > + * @req: The request
> > + *
> > + * Mark that the request has to be manually completed by calling
> > + * media_request_manual_complete().
> > + *
> > + * This function should be called in the req_queue callback.
>
> s/should/shall/ unless it's not a hard requirement. Any way to catch
> incorrect call patterns ?
>
> > + */
> > +static inline void
> > +media_request_mark_manual_completion(struct media_request *req)
> > +{
> > + req->manual_completion = true;
> > +}
> > +
> > +/**
> > + * media_request_manual_complete - Set manual_completion to false
>
> The main purpose of the function is to complete the request, not setting
> manual_completion to false.
>
> > + *
> > + * @req: The request
> > + *
> > + * Set @manual_completion to false, and if @num_incomplete_objects
> > + * is 0, then mark the request as completed.
> > + *
> > + * If there are still incomplete objects in the request, then
> > + * WARN for that since that suggests a driver error.
>
> If that's an error then I'd document it more explicitly, as the first
> sentence makes it sound that both cases are valid. Maybe
>
> * This function completes a request that was marked for manual completion by an
> * earlier call to media_request_mark_manual_completion(). The request's
> * @manual_completion flag is reset to false.
> *
> * All objects contained in the request must have been completed previously. It
> * is an error to call this function otherwise. The request will not be
> * completed in that case, and the function will WARN.
>
> > + */
> > +void media_request_manual_complete(struct media_request *req);
> > +
> > #else
> >
> > static inline void media_request_get(struct media_request *req)
> > @@ -336,7 +370,7 @@ void media_request_object_init(struct media_request_object *obj);
> > * @req: The media request
> > * @ops: The object ops for this object
> > * @priv: A driver-specific priv pointer associated with this object
> > - * @is_buffer: Set to true if the object a buffer object.
> > + * @is_buffer: Set to true if the object is a buffer object.
> > * @obj: The object
> > *
> > * Bind this object to the request and set the ops and priv values of
--
Nicolas Dufresne
Principal Engineer at Collabora
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