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 7F8C3155726; Fri, 29 Nov 2024 11:06:52 +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=1732878414; cv=none; b=WAqwSevw0g43u+rV4CTgMl4InYf2QN+FBwquRfgQQTFgpPpMxQRNpfu8Sag4v4h6Jxj6Jw00ptc9HHH+OcJh+Iij+P70iYE7+U+GJD3xEIGBCd2Amq61KTQXJiJhsY3/x5UZGelpKeAwns6k5cGMiXqEj5SYQ5o45T6vDfc7e1I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732878414; c=relaxed/simple; bh=TwdrBaS4qYS6OdOtx8q9Yeagwt8UgVRcTEqq9YSfMBc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=n1uhqG7BbsI4f9GQcd76mq+yGSSogNALnj5GSoFuJmnXJa0LpD+rYVdgT+/+ZpSihgYueTse9qxMqzPW5XezX+GOQZruxUqTvT2oEJpoMfBwk/jBSEf3xOf5cIPiQUC6Vu1e1nHnBvMiJxuoi2anib/7yscEJNZtRVCsA5SjiEU= 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=qxxpXQsA; 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="qxxpXQsA" Received: from pendragon.ideasonboard.com (81-175-209-231.bb.dnainternet.fi [81.175.209.231]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 469E7A8F; Fri, 29 Nov 2024 12:06:26 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1732878386; bh=TwdrBaS4qYS6OdOtx8q9Yeagwt8UgVRcTEqq9YSfMBc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=qxxpXQsA+neGZrBhgXAjDjR7ecZQv87V4hi+PuFEC0EtZC4tTdf/sEmYL5SKXenKc dCyPI9qK9WzNVqmhOs/ZtDFWNeTbJhj0u5OIPUlmoI0ATGmHk1gp7l2lcrT06H7Vez KwcIIDX+QcV3IFgKX2CluVcPheiAQ09ItDPhcvFY= Date: Fri, 29 Nov 2024 13:06:40 +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: <20241129110640.GB4108@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> Precedence: bulk X-Mailing-List: linux-kernel@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 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. > - 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