Re: [PATCH v2 1/5] media: mc: add manual request completion

[Nicolas Dufresne <nicolas.dufresne@collabora.com>]

Replying on the code comment, sorry for missing some bit earlier ...

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@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.
> 
> > 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 | 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.

I agree, it sounds like an invitation to write it directly, we don't
really want this. If Hans is fine I'll drop it.

> 
> > + * 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 ?

I think we should be more strict, I can edit to shall.

About ways to check, perhaps I can add a lockdep_assert_held() on the
mdev->req_queue_mutex along with checking that the state is QUEUED. The
state check would catch trying to do so in req_validate().

> 
> > + */
> > +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.

Indeed, that's documenting an implementation detail.

> 
> > + *
> > + * @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

Its a programming error, I should rephrase this in the next version.

> 
>  * 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

thanks a lot for the review,

-- 
Nicolas Dufresne
Principal Engineer at Collabora