From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 345AAC10F1B for ; Fri, 30 Dec 2022 14:38:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234899AbiL3OiC (ORCPT ); Fri, 30 Dec 2022 09:38:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33490 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229505AbiL3OiA (ORCPT ); Fri, 30 Dec 2022 09:38:00 -0500 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 951591901E; Fri, 30 Dec 2022 06:37:57 -0800 (PST) Received: from pendragon.ideasonboard.com (213-243-189-158.bb.dnainternet.fi [213.243.189.158]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id E8D452F5; Fri, 30 Dec 2022 15:37:55 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1672411076; bh=XnXoPl0/oTF/xEWJsb6tZooAxDcN8WbanoTfny0E5lQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Mw0goLIbKld12s8iBzuSOHgRhJKR7suovCSRb33Ato5970iSXCaXellDPX4scibeU td7SjRb4NjLYxI7SWI+mLuePiWLihxaBhuZaJAwsnHCF7ciUchkS1zSihq+Jn4PkKy Ob7RHN6EorzgzGxGkjnTXbsAHNME0v+1CiJO87/I= Date: Fri, 30 Dec 2022 16:37:51 +0200 From: Laurent Pinchart To: Ricardo Ribalda Cc: Mauro Carvalho Chehab , "hn.chen" , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RESEND v2 6/8] media: uvcvideo: Allow hw clock updates with buffers not full Message-ID: References: <20220920-resend-hwtimestamp-v2-0-0d7978a817cc@chromium.org> <20220920-resend-hwtimestamp-v2-6-0d7978a817cc@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20220920-resend-hwtimestamp-v2-6-0d7978a817cc@chromium.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ricardo, Thank you for the patch. On Fri, Dec 02, 2022 at 06:02:46PM +0100, Ricardo Ribalda wrote: > With UVC 1.5 we get as little as one clock sample per frame. Which means > that it takes 32 frames to move from the software timestamp to the > hardware timestamp method. > > This results in abrupt changes in the timestamping after 32 frames (~1 > second), resulting in noticeable artifacts when used for encoding. > > With this patch we modify the update algorithm to work with whatever > amount of values are available. This too makes me thing that we should *really* move this to userspace. It will but much easier to implement clock domain translation there, with a better precision. > Tested-by: HungNien Chen > Signed-off-by: Ricardo Ribalda > --- > drivers/media/usb/uvc/uvc_video.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c > index 75c32e232f5d..7c6448c6d706 100644 > --- a/drivers/media/usb/uvc/uvc_video.c > +++ b/drivers/media/usb/uvc/uvc_video.c > @@ -742,10 +742,10 @@ void uvc_video_clock_update(struct uvc_streaming *stream, > > spin_lock_irqsave(&clock->lock, flags); > > - if (clock->count < clock->size) > + if (clock->count < 2) > goto done; > > - first = &clock->samples[clock->head]; > + first = &clock->samples[(clock->head - clock->count) % clock->size]; > last = &clock->samples[(clock->head - 1) % clock->size]; > > /* First step, PTS to SOF conversion. */ > @@ -760,6 +760,14 @@ void uvc_video_clock_update(struct uvc_streaming *stream, > if (y2 < y1) > y2 += 2048 << 16; > > + /* > + * Have at least 1/4 of a second of timestamps before we > + * try to do any calculation. Otherwise we do not have enough > + * precission. s/precission/precision/ How did you determine 250ms was the right threshold ? > + */ > + if ((y2 - y1) < (256 << 16)) > + goto done; > + > y = (u64)(y2 - y1) * (1ULL << 31) + (u64)y1 * (u64)x2 > - (u64)y2 * (u64)x1; > y = div_u64(y, x2 - x1); > -- Regards, Laurent Pinchart