On 29/11/2024 12:54, Ricardo Ribalda wrote: > On Fri, 29 Nov 2024 at 12:06, Laurent Pinchart > <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: >> >> On Fri, Nov 29, 2024 at 11:59:27AM +0100, Ricardo Ribalda wrote: >>> On Fri, 29 Nov 2024 at 11:36, Hans Verkuil wrote: >>>> On 28/11/2024 23:33, Laurent Pinchart wrote: >>>>> On Thu, Nov 28, 2024 at 11:28:29PM +0100, Ricardo Ribalda wrote: >>>>>> On Thu, 28 Nov 2024 at 23:22, Laurent Pinchart wrote: >>>>>>> >>>>>>> Hi Ricardo, >>>>>>> >>>>>>> (CC'ing Hans Verkuil) >>>>>>> >>>>>>> Thank you for the patch. >>>>>>> >>>>>>> On Wed, Nov 27, 2024 at 12:14:50PM +0000, Ricardo Ribalda wrote: >>>>>>>> If a file handle is waiting for a response from an async control, avoid >>>>>>>> that other file handle operate with it. >>>>>>>> >>>>>>>> Without this patch, the first file handle will never get the event >>>>>>>> associated with that operation, which can lead to endless loops in >>>>>>>> applications. Eg: >>>>>>>> If an application A wants to change the zoom and to know when the >>>>>>>> operation has completed: >>>>>>>> it will open the video node, subscribe to the zoom event, change the >>>>>>>> control and wait for zoom to finish. >>>>>>>> If before the zoom operation finishes, another application B changes >>>>>>>> the zoom, the first app A will loop forever. >>>>>>> >>>>>>> Hans, the V4L2 specification isn't very clear on this. I see pros and >>>>>>> cons for both behaviours, with a preference for the current behaviour, >>>>>>> as with this patch the control will remain busy until the file handle is >>>>>>> closed if the device doesn't send the control event for any reason. What >>>>>>> do you think ? >>>>>> >>>>>> Just one small clarification. The same file handler can change the >>>>>> value of the async control as many times as it wants, even if the >>>>>> operation has not finished. >>>>>> >>>>>> It will be other file handles that will get -EBUSY if they try to use >>>>>> an async control with an unfinished operation started by another fh. >>>>> >>>>> Yes, I should have been more precised. If the device doesn't send the >>>>> control event, then all other file handles will be prevented from >>>>> setting the control until the file handle that set it first gets closed. >>>> >>>> I think I need a bit more background here: >>>> >>>> First of all, what is an asynchronous control in UVC? I think that means >>>> you can set it, but it takes time for that operation to finish, so you >>>> get an event later when the operation is done. So zoom and similar operations >>>> are examples of that. >>>> >>>> And only when the operation finishes will the control event be sent, correct? >>> >>> You are correct. This diagrams from the spec is more or less clear: >>> https://ibb.co/MDGn7F3 >>> >>>> While the operation is ongoing, if you query the control value, is that reporting >>>> the current position or the final position? >>> >>> I'd expect hardware will return either the current position, the start >>> position or the final position. I could not find anything in the spec >>> that points in one direction or the others. >> >> Figure 2-21 in UVC 1.5 indicates that the device should STALL the >> GET_CUR and SET_CUR requests if a state change is in progress. >> >>> And in the driver I believe that we might have a bug handling this >>> case (will send a patch if I can confirm it) >>> the zoom is at 0 and you set it 10 >>> if you read the value 2 times before the camera reaches value 10: >>> - First value will come from the hardware and the response will be cached >> >> Only if the control doesn't have the auto-update flag set, so it will be >> device-dependent. As GET_CUR should stall that's not really relevant, >> except for the fact that devices may not stall the request. > > I missed that the device will likely stall during async operations. > > What do you think of something like this? I believe it can work with > compliant and non compliant devices. > Note that the event will be received by the device that originated the > operation, not to the second one that might receive an error during > write/read. > > > > diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c > index 4fe26e82e3d1..9a86c912e7a2 100644 > --- a/drivers/media/usb/uvc/uvc_ctrl.c > +++ b/drivers/media/usb/uvc/uvc_ctrl.c > @@ -1826,14 +1826,15 @@ static int uvc_ctrl_commit_entity(struct > uvc_device *dev, > continue; > > /* > - * Reset the loaded flag for auto-update controls that were > + * Reset the loaded flag for auto-update controls and for > + * asynchronous controls with pending operations, that were > * marked as loaded in uvc_ctrl_get/uvc_ctrl_set to prevent > * uvc_ctrl_get from using the cached value, and for write-only > * controls to prevent uvc_ctrl_set from setting bits not > * explicitly set by the user. > */ > if (ctrl->info.flags & UVC_CTRL_FLAG_AUTO_UPDATE || > - !(ctrl->info.flags & UVC_CTRL_FLAG_GET_CUR)) > + !(ctrl->info.flags & UVC_CTRL_FLAG_GET_CUR) || ctrl->handle) > ctrl->loaded = 0; > > if (!ctrl->dirty) > @@ -2046,8 +2047,18 @@ int uvc_ctrl_set(struct uvc_fh *handle, > mapping->set(mapping, value, > uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT)); > > - if (ctrl->info.flags & UVC_CTRL_FLAG_ASYNCHRONOUS) > - ctrl->handle = handle; > + if (ctrl->info.flags & UVC_CTRL_FLAG_ASYNCHRONOUS) { > + /* > + * Other file handle is waiting for an operation on > + * this asynchronous control. If the device is compliant > + * this operation will fail. > + * > + * Do not replace the handle pointer, so the original file > + * descriptor will get the completion event. > + */ > + if (!ctrl->handle) > + ctrl->handle = handle; I don't think this is right: you want the completion event for async controls to go to all filehandles that are subscribed to that control. Which is what happens if handle == NULL (as I understand the code). Regards, Hans > + } > > ctrl->dirty = 1; > ctrl->modified = 1; > >> >>> - Second value will be the cached one >>> >>> now the camera is at zoom 10 >>> If you read the value, you will read the cached value >>> >>>> E.g.: the zoom control is at value 0 and I set it to 10, then I poll the zoom control >>>> value: will that report the intermediate values until it reaches 10? And when it is >>>> at 10, the control event is sent? >>>> >>>>>>>> Cc: stable@xxxxxxxxxxxxxxx >>>>>>>> Fixes: e5225c820c05 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives") >>>>>>>> Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx> >>>>>>>> --- >>>>>>>> drivers/media/usb/uvc/uvc_ctrl.c | 4 ++++ >>>>>>>> 1 file changed, 4 insertions(+) >>>>>>>> >>>>>>>> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c >>>>>>>> index b6af4ff92cbd..3f8ae35cb3bc 100644 >>>>>>>> --- a/drivers/media/usb/uvc/uvc_ctrl.c >>>>>>>> +++ b/drivers/media/usb/uvc/uvc_ctrl.c >>>>>>>> @@ -1955,6 +1955,10 @@ int uvc_ctrl_set(struct uvc_fh *handle, >>>>>>>> if (!(ctrl->info.flags & UVC_CTRL_FLAG_SET_CUR)) >>>>>>>> return -EACCES; >>>>>>>> >>>>>>>> + /* Other file handle is waiting a response from this async control. */ >>>>>>>> + if (ctrl->handle && ctrl->handle != handle) >>>>>>>> + return -EBUSY; >>>>>>>> + >>>>>>>> /* Clamp out of range values. */ >>>>>>>> switch (mapping->v4l2_type) { >>>>>>>> case V4L2_CTRL_TYPE_INTEGER: >> >> -- >> Regards, >> >> Laurent Pinchart > > >
