On Fri, 29 Nov 2024 at 14:13, Hans Verkuil <hverkuil-cisco@xxxxxxxxx> wrote: > > 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, The code is correct, but the comment is not :). It should say: * Do not replace the handle pointer, or the originator of * the operation will receive an event. The originar should NOT receive the event.
