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 0265D286AE; Mon, 19 Feb 2024 10:40:42 +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=1708339244; cv=none; b=jQA68sUbdQqDPxwjjvCK6dvJjGpDfOAr7zz2BoHBnZighyBOa16M5p/9I59pkuhpUTuueBLUUQbxFqi3nfYMynPGXIv9R+YmoHPFQOaKTJ8Kq+/jSPX4GyBa/hjGBsV/K2TWJCbnLPpnsrYkTH/CF1xhHvSiIKtZlIiOfkj9dn8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708339244; c=relaxed/simple; bh=EsN/+7thfuLmfHd8qe3dlDirPQrVnNo5wOQUpPckTFM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=FabHMd3KcNF6w9/2RdrYcY4Ia48o8vi3K6I+3a8gl0dWSF71flLOT1pL4j8ZNr8z2Vv7c1WxqgZqb5zylCSn9ynoe85NyCJUYe6A/MX9wulxqsmXy3ZEPbwFyif1Lpsbcf7PKjI1PxWfLTSlPySpyDJCx63Lzn92jLo3HC/SQuI= 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=aOUsX6hq; 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="aOUsX6hq" Received: from pendragon.ideasonboard.com (89-27-53-110.bb.dnainternet.fi [89.27.53.110]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 05DB966F; Mon, 19 Feb 2024 11:40:34 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1708339235; bh=EsN/+7thfuLmfHd8qe3dlDirPQrVnNo5wOQUpPckTFM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=aOUsX6hqtRgcpJKKdJwVdfS6Ke3wRdZUpyPOpuis7GGI4TmZqH6I59LTyWOyjwwR8 kgqZRghP3W7mVOE0ua09idjToY1KmSNjwqx9R5dHkBaXpEFjqmgZsSoqAHTsMn3e3F jydIgBCvZHEBy85R1g3PNuZVpNS++Q07MAOVjKas= Date: Mon, 19 Feb 2024 12:40:46 +0200 From: Laurent Pinchart To: Ricardo Ribalda Cc: Mauro Carvalho Chehab , Sergey Senozhatsky , linux-kernel@vger.kernel.org, "hn.chen" , linux-media@vger.kernel.org Subject: Re: [PATCH v9 1/6] media: uvcvideo: Fix negative modulus calculation Message-ID: <20240219104046.GB13043@pendragon.ideasonboard.com> References: <20220920-resend-hwtimestamp-v9-0-55a89f46f6be@chromium.org> <20220920-resend-hwtimestamp-v9-1-55a89f46f6be@chromium.org> <20240212225940.GA19316@pendragon.ideasonboard.com> Precedence: bulk X-Mailing-List: linux-media@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: Hi Ricardo, On Mon, Feb 19, 2024 at 11:28:03AM +0100, Ricardo Ribalda wrote: > On Mon, 12 Feb 2024 at 23:59, Laurent Pinchart wrote: > > On Wed, Mar 15, 2023 at 02:30:12PM +0100, Ricardo Ribalda wrote: > > > If head is 0, last will be addressing the index 0 instead of clock->size > > > -1. Luckily clock->head is unsiged, otherwise it would be addressing > > > 0xffffffff. > > > > I'm not following you. In the expression > > > > (clock->head - 1) % clock->size > > > > clock->head is an unsigned int, and 1 as a signed int, so the result of > > the subtraction is promoted to an unsigned int. When clock->head is 0, the expression evaluates to > > > > 0xffffffff % clock->size > > > > clock->size is a power of two (hardcoded to 32 at the moment), so the > > expression evaluates to 31, as intended. > > > > Am I missing something ? > > Take a look to: https://godbolt.org/z/xYeqTx6ba > > The expression only works because the size is a power of two. In this > set I am allowing sizes that are not powers of two. Could you then update the commit message to explain that ? I'll review the rest of the series this week. > > > Nontheless, this is not the intented behaviour and should be fixed. > > > > > > Fixes: 66847ef013cc ("[media] uvcvideo: Add UVC timestamps support") > > > Signed-off-by: Ricardo Ribalda > > > --- > > > drivers/media/usb/uvc/uvc_video.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c > > > index d4b023d4de7c..4ff4ab4471fe 100644 > > > --- a/drivers/media/usb/uvc/uvc_video.c > > > +++ b/drivers/media/usb/uvc/uvc_video.c > > > @@ -732,7 +732,7 @@ void uvc_video_clock_update(struct uvc_streaming *stream, > > > goto done; > > > > > > first = &clock->samples[clock->head]; > > > - last = &clock->samples[(clock->head - 1) % clock->size]; > > > + last = &clock->samples[(clock->head - 1 + clock->size) % clock->size]; > > > > > > /* First step, PTS to SOF conversion. */ > > > delta_stc = buf->pts - (1UL << 31); -- Regards, Laurent Pinchart