On Fri, Nov 29, 2024 at 02:37:21PM +0100, Ricardo Ribalda wrote: > On Fri, 29 Nov 2024 at 14:10, Hans Verkuil wrote: > > On 29/11/2024 12:06, Laurent Pinchart 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. > > > > OK, that helps a lot. > > > > If an operation is in progress, then setting a new control value should > > result in -EBUSY. Based on the description above, I gather that even the > > same fh that made the request cannot update it while the operation is > > ongoing? > > That is correct according to the spec. But both Laurent (correct me if > I am wrong) and me suspect that there are devices that do not > implement this properly. With UVC it's more than suspicion. Whatever the feature, there's bound to be a device that gets it wrong. The more niche the feature is, the worse it can get. > > Getting the control should just return the value that was set. I assume > > that is cached in uvc? > > If I get the code right... we only return the cached value when the > field "loaded" is true. That happens when we read the device. So if > the driver is just loaded > > write(full controlA) > read(full controlA) > read(full controlA) > > The first read will get the value from the hardware, the second will be cached. It depends if the control is marked as auto-update or not. This is orthogonal to asynchronous controls, so we shouldn't rely on it. > > >> - 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
