From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7485AAD23; Fri, 29 Nov 2024 21:47:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.167.242.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732916855; cv=none; b=Nx6tjUrZD3ATNiJqPVBQV/EXUAGD2ir+uokNdRmmN6bQR52UQl8pOsvTH1CeaAA9QMDNcoAMO8x3jDKShI7sG5VktGYVG211SvY/gmJg7w8fz1TXbVMQxXuouiQl+aLCyyuNgFt7lIpT0LDkAOMER0aJUQL9HPwszqEfETNVFMg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732916855; c=relaxed/simple; bh=PF3GFjspWJnSYtUmztFn/TtoY/RO/NVPnT77nVDnEWA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=MDP6N4nxmbNIlSjv337FOT4+GX8dd568gBM94+dB3hghieoS/t1RS7flvoHrZ5cmvrNfkHoekzynwikYT6RuL3qiR5zndiTtx9a6j6/U2i0CdJ1T+1+garDEqKFVsDxwikljactzQYW7yt2h6dbIc3jy6be6cZyiZogskqQ4F5o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com; spf=pass smtp.mailfrom=ideasonboard.com; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b=c/1691Db; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="c/1691Db" Received: from pendragon.ideasonboard.com (81-175-209-231.bb.dnainternet.fi [81.175.209.231]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id AF6EAA57; Fri, 29 Nov 2024 22:47:06 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1732916826; bh=PF3GFjspWJnSYtUmztFn/TtoY/RO/NVPnT77nVDnEWA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=c/1691Db8olWVQlmo4MpchhysfUkcsOEE+t+2IlIWm+QBM5NO6t3PkEM0/QhcHFjE 5Yi5Ovi7SVInWjYBdsMxjbW1ukqlLn3AAn9DqplfKu3t/vJej5WQvMEnSYK1/sjkyq PTHyvn2RrLZgeYEj6Eul9t2tTtO6AKvM0tb1Tu+U= Date: Fri, 29 Nov 2024 23:47:21 +0200 From: Laurent Pinchart To: Ricardo Ribalda Cc: Hans Verkuil , Hans de Goede , Mauro Carvalho Chehab , Guennadi Liakhovetski , Mauro Carvalho Chehab , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2 2/4] media: uvcvideo: Do not set an async control owned by other fh Message-ID: <20241129214721.GC2652@pendragon.ideasonboard.com> References: <20241127-uvc-fix-async-v2-0-510aab9570dd@chromium.org> <20241127-uvc-fix-async-v2-2-510aab9570dd@chromium.org> <20241128222232.GF25731@pendragon.ideasonboard.com> <20241128223343.GH25731@pendragon.ideasonboard.com> <7eeab6bd-ce02-41a6-bcc1-7c2750ce0359@xs4all.nl> <20241129110640.GB4108@pendragon.ideasonboard.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: 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@vger.kernel.org > > >>>>>>> Fixes: e5225c820c05 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives") > > >>>>>>> Signed-off-by: Ricardo Ribalda > > >>>>>>> --- > > >>>>>>> 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