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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=Lcx4cKOb; 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="Lcx4cKOb" Received: from pendragon.ideasonboard.com (81-175-209-231.bb.dnainternet.fi [81.175.209.231]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 5320AC21; Thu, 28 Nov 2024 21:45:06 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1732826706; bh=UMYE0eAAYmB/PkcRW6ZCnIx6X+WRhj8jM3geWSVcjZI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Lcx4cKObeZiwGP3FOLTXu/Yte4QaG1tNMlAPAy3OJsu1+qmhPqLaRIEM5x/eEboia 0AhSvccogyMoTvrveonE5ld3ossGD5c1WObhtmrWTJn1+enCjo7EyzlZPYVPOltUcJ H5ZCVJI8PALVokCWHpIINSRReiIsWiXnMAoWFQLM= Date: Thu, 28 Nov 2024 22:45:19 +0200 From: Laurent Pinchart To: Ricardo Ribalda Cc: Hans de Goede , Mauro Carvalho Chehab , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, Sakari Ailus , stable@vger.kernel.org Subject: Re: [PATCH v4 1/2] media: uvcvideo: Support partial control reads Message-ID: <20241128204519.GA25731@pendragon.ideasonboard.com> References: <20241120-uvc-readless-v4-0-4672dbef3d46@chromium.org> <20241120-uvc-readless-v4-1-4672dbef3d46@chromium.org> <20241126180616.GL5461@pendragon.ideasonboard.com> <20241127083444.GV5461@pendragon.ideasonboard.com> <20241127091400.GB31095@pendragon.ideasonboard.com> 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 Wed, Nov 27, 2024 at 10:35:54AM +0100, Ricardo Ribalda wrote: > On Wed, 27 Nov 2024 at 10:14, Laurent Pinchart wrote: > > On Wed, Nov 27, 2024 at 09:58:21AM +0100, Ricardo Ribalda wrote: > > > On Wed, 27 Nov 2024 at 09:34, Laurent Pinchart wrote: > > > > On Tue, Nov 26, 2024 at 07:12:53PM +0100, Ricardo Ribalda wrote: > > > > > On Tue, 26 Nov 2024 at 19:06, Laurent Pinchart wrote: > > > > > > On Wed, Nov 20, 2024 at 03:26:19PM +0000, Ricardo Ribalda wrote: > > > > > > > Some cameras, like the ELMO MX-P3, do not return all the bytes > > > > > > > requested from a control if it can fit in less bytes. > > > > > > > Eg: Returning 0xab instead of 0x00ab. > > > > > > > usb 3-9: Failed to query (GET_DEF) UVC control 3 on unit 2: 1 (exp. 2). > > > > > > > > > > > > > > Extend the returned value from the camera and return it. > > > > > > > > > > > > > > Cc: stable@vger.kernel.org > > > > > > > Fixes: a763b9fb58be ("media: uvcvideo: Do not return positive errors in uvc_query_ctrl()") > > > > > > > Reviewed-by: Hans de Goede > > > > > > > Signed-off-by: Ricardo Ribalda > > > > > > > --- > > > > > > > drivers/media/usb/uvc/uvc_video.c | 16 ++++++++++++++++ > > > > > > > 1 file changed, 16 insertions(+) > > > > > > > > > > > > > > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c > > > > > > > index cd9c29532fb0..482c4ceceaac 100644 > > > > > > > --- a/drivers/media/usb/uvc/uvc_video.c > > > > > > > +++ b/drivers/media/usb/uvc/uvc_video.c > > > > > > > @@ -79,6 +79,22 @@ int uvc_query_ctrl(struct uvc_device *dev, u8 query, u8 unit, > > > > > > > if (likely(ret == size)) > > > > > > > return 0; > > > > > > > > > > > > > > + /* > > > > > > > + * In UVC the data is usually represented in little-endian. > > > > > > > > > > > > I had a comment about this in the previous version, did you ignore it on > > > > > > purpose because you disagreed, or was it an oversight ? > > > > > > > > > > I rephrased the comment. I added "usually" to make it clear that it > > > > > might not be the case for all the data types. Like composed or xu. > > > > > > > > Ah, that's what you meant by "usually". I read it as "usually in > > > > little-endian, but could be big-endian too", which confused me. > > > > > > > > Data types that are not integers will not work nicely with the > > > > workaround below. How do you envision that being handled ? Do you > > > > consider that the device will return too few bytes only for integer data > > > > types, or that affected devices don't have controls that use compound > > > > data types ? I don't see what else we could do so I'd be fine with such > > > > a heuristic for this workaround, but it needs to be clearly explained. > > > > > > Non integer datatypes might work if the last part of the data is > > > expected to be zero. > > > I do not think that we can find a heuristic that can work for all the cases. > > > > > > For years we have ignored partial reads and it has never been an > > > issue. I vote for not adding any heuristics, the logging should help > > > identify future issues (if there is any). > > > > What you're doing below is already a heuristic :-) I don't think the > > code needs to be changed, but I'd like this comment to explain why we > > consider that the heuristic in this patch is fine, to help the person > > (possibly you or me) who will read this code in a year and wonder what's > > going on. > > What about: > > * Some devices return shorter USB control packets than expected if the > * returned value can fit in less bytes. Zero all the bytes that the > * device has not written. > * > * This quirk is applied to all datatypes, even to non little-endian integers > * or composite values. We exclude UVC_GET_INFO from the quirk. > * UVC_GET_LEN does not need to be excluded because its size is > * always 1. For the second paragraph you could write * This quirk is applied to all controls, regardless of their data type. Most * controls are little-endian integers, in which case the missing bytes become 0 * MSBs. For other data types, a different heuristic could be implemented if a * device is found needing it. * * We exclude UVC_GET_INFO from the quirk. UVC_GET_LEN does not need to be * excluded because its size is always 1. > > > > > I also r/package/packet/ > > > > > > > > > > Did I miss another comment? > > > > > > > > > > > > + * Some devices return shorter USB control packets that expected if the > > > > > > > + * returned value can fit in less bytes. Zero all the bytes that the > > > > > > > + * device have not written. > > > > > > > > > > > > s/have/has/ > > > > > > > > > > > > And if you meant to start a new paragraph here, a blank line is missing. > > > > > > Otherwise, no need to break the line before 80 columns. > > > > > > > > > > The patch is already in the uvc tree. How do you want to handle this? > > > > > > > > The branch shared between Hans and me can be rebased, it's a staging > > > > area. > > > > > > I will send a new version, fixing the typo. and the missing new line. > > > I will also remove the sentence > > > `* In UVC the data is usually represented in little-endian.` > > > It is confusing. > > > > > > > > > > + * We exclude UVC_GET_INFO from the quirk. UVC_GET_LEN does not need to > > > > > > > + * be excluded because its size is always 1. > > > > > > > + */ > > > > > > > + if (ret > 0 && query != UVC_GET_INFO) { > > > > > > > + memset(data + ret, 0, size - ret); > > > > > > > + dev_warn_once(&dev->udev->dev, > > > > > > > + "UVC non compliance: %s control %u on unit %u returned %d bytes when we expected %u.\n", > > > > > > > + uvc_query_name(query), cs, unit, ret, size); > > > > > > > + return 0; > > > > > > > + } > > > > > > > + > > > > > > > if (ret != -EPIPE) { > > > > > > > dev_err(&dev->udev->dev, > > > > > > > "Failed to query (%s) UVC control %u on unit %u: %d (exp. %u).\n", -- Regards, Laurent Pinchart