Re: [PATCH v3 1/5] media: mc: add manual request completion

Sakari Ailus
2025-06-05T06:53:38Z

Hi Nicolas,

On Wed, Jun 04, 2025 at 07:19:27PM -0400, Nicolas Dufresne wrote:
> Le mercredi 04 juin 2025 à 21:04 +0000, Sakari Ailus a écrit :
> > Hi Nicolas,
> >
> > Thanks for the update.
> >
> > On Wed, Jun 04, 2025 at 04:09:35PM -0400, Nicolas Dufresne wrote:
> > > From: Hans Verkuil <hverkuil@xs4all.nl>
> > >
> > > By default when the last request object is completed, the whole
> > > request completes as well.
> > >
> > > But sometimes you want to delay this completion to an arbitrary point in
> > > time so add a manual complete mode for this.
> > >
> > > 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@xs4all.nl>
> > > Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
> > > ---
> > >  drivers/media/mc/mc-request.c | 38 ++++++++++++++++++++++++++++++++++++--
> > >  include/media/media-request.h | 38 +++++++++++++++++++++++++++++++++++++-
> > >  2 files changed, 73 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;
> >
> > I'd declare flags as last.
> >
> > > + bool completed = false;
> > > +
> > > + if (WARN_ON(!req))
> > > + return;
> > > + if (WARN_ON(!req->manual_completion))
> > > + return;
> >
> > I think I'd use WARN_ON_ONCE() consistently: this is a driver (or
> > framework) bug and telling once about it is very probably enough.
>
> Just to be sure, you only mean for the two checks above ? Or did
> you mean for the entire function ?

For the entire function. I thought that if this is user-triggerable, the
amount of data ending up in logs could be very large.

>
> >
> > > +
> > > + spin_lock_irqsave(&req->lock, flags);
>
> In practice, if you call this specific function from two places at the same
> time you have a bug, but I realize that moving the the warning on the check
> manual_completion inside that lock would massively help detect that case.
>
> What do you think ?

Seems reasonable to me.

>
> > > + 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;
> > > + }
> >
> > A newline would be nice here.
> >
> > > +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..7f9af68ef19ac6de0184bbb0c0827dc59777c6dc 100644
> > > --- a/include/media/media-request.h
> > > +++ b/include/media/media-request.h
> > > @@ -56,6 +56,9 @@ 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 complete the request after @num_incomplete_objects == 0.
> > >   * @poll_wait: Wait queue for poll
> > >   * @lock: Serializes access to this struct
> > >   */
> > > @@ -68,6 +71,7 @@ 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 +222,38 @@ 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 - Enable manual completion
> > > + *
> > > + * @req: The request
> > > + *
> > > + * Mark that the request has to be manually completed by calling
> > > + * media_request_manual_complete().
> > > + *
> > > + * This function shall be called in the req_queue callback.
> > > + */
> > > +static inline void
> > > +media_request_mark_manual_completion(struct media_request *req)
> > > +{
> > > + req->manual_completion = true;
> > > +}
> > > +
> > > +/**
> > > + * media_request_manual_complete - Mark the request as completed
> > > + *
> > > + * @req: The request
> > > + *
> > > + * 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.
> >
> > s/flag/field/
> >
> > > + *
> > > + * All objects contained in the request must have been completed previously. It
> > > + * is an error to call this function otherwise. If such an error occurred, the
> > > + * function will WARN and the object completion will be delayed until
> > > + * @num_incomplete_objects is 0.
> > > + */
> > > +void media_request_manual_complete(struct media_request *req);
> > > +
> > >  #else
> > >
> > >  static inline void media_request_get(struct media_request *req)
> > > @@ -336,7 +372,7 @@ 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
> > >

--
Kind regards,

Sakari Ailus