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 X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6410DC07E9A for ; Wed, 14 Jul 2021 18:40:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 37CAD613CA for ; Wed, 14 Jul 2021 18:40:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229806AbhGNSnr (ORCPT ); Wed, 14 Jul 2021 14:43:47 -0400 Received: from perceval.ideasonboard.com ([213.167.242.64]:57132 "EHLO perceval.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229603AbhGNSnq (ORCPT ); Wed, 14 Jul 2021 14:43:46 -0400 Received: from pendragon.ideasonboard.com (62-78-145-57.bb.dnainternet.fi [62.78.145.57]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id E6B2BCC; Wed, 14 Jul 2021 20:40:52 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1626288053; bh=RXoS7uOvpB5VAFXYDu8/3wKv0zzhGVf+fnUveMwoIj4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=qPVHrCjjdWs4tRxJ93jLG6HYAIADnBtC++iJnkXd5xkVn0Aww1P1oWVW+lhUZj0Mg EkLmqnjqvGFi8cfkh2oxikV6m4uZ1h5UBi8o7qU0HZY47PaqXeB6wQdL6OTnOOs6W8 tpM01/D8ncEFVCgyOxTiNwciOeEzxDuv8n7TAEJY= Date: Wed, 14 Jul 2021 21:40:51 +0300 From: Laurent Pinchart To: Niklas =?utf-8?Q?S=C3=B6derlund?= Cc: Dennis Rachui , Steve Longerbeam , Mauro Carvalho Chehab , Maxime Ripard , Sakari Ailus , linux-media@vger.kernel.org, linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] media: rcar-csi2: do not update format while streaming Message-ID: References: <1625750578-108454-1-git-send-email-drachui@de.adit-jv.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-renesas-soc@vger.kernel.org Hi Niklas, On Tue, Jul 13, 2021 at 11:42:17AM +0200, Niklas Söderlund wrote: > On 2021-07-11 01:42:44 +0300, Laurent Pinchart wrote: > > On Fri, Jul 09, 2021 at 04:20:40PM +0200, Niklas Söderlund wrote: > > > On 2021-07-08 15:22:58 +0200, Dennis Rachui wrote: > > > > Verify that streaming is not active before setting the pad format. > > > > > > > > According to the VIDIOC documentation [1] changes to the active > > > > format of a media pad via the VIDIOC_SUBDEV_S_FMT ioctl are > > > > applied to the underlying hardware. > > > > In rcar-csi2 a format change only applies to hardware, when the > > > > pipeline is started. While the device is not in use, it is therefore > > > > okay to update the format. > > > > > > > > However, when the pipeline is active, this leads to a format > > > > mismatch between driver and device. > > > > Other applications can query the format with > > > > VIDIOC_SUBDEV_G_FMT at any time and would be reported > > > > a format that does not fit the current stream. > > > > > > > > This commit prevents format update while streaming is active > > > > and returns -EBUSY to user space, as suggested by [1]. > > > > > > > > [1] Documentation/userspace-api/media/v4l/vidioc-subdev-g-fmt.rst > > > > > > I like that this is addressed, but I wonder is this not something that > > > should be fixed in the V4L2 core and not in drivers? > > > > Some drivers may support format changes during streaming (that's allowed > > by the V4L2 API, I'm not sure if it's used anywhere though). While I'd > > favour not duplicating the same logic in different (and differently > > buggy) ways in drivers, I'm not sure how this could be implemented in a > > sane way in the V4L2 core in its current state. > > I understand it's possible from some devices to support to format > changes during streaming, but as you point out it's the exception and > not the rule, if used at all. > > So my point is if we start to enforce this in drivers we are headed down > a road where this will be messier to clean up. Would it not make more > sens to default the V4L2 core to disallow format changes while streaming > and add a new flag to V4L2_SUBDEV_CAP_ to signal that the subdevice > supports format changes while streaming? > > We already have V4L2_SUBDEV_CAP_RO_SUBDEV to signal that a subdevice > only supports read-only operations so I think it would not be too hard > to move this functionality into the core? Yes, that's something we could try. The subdev core will then need to track the streaming state, which may require wrapping the .s_stream() call. Locking should then also likely be handled by the core. Probably nothing impossible, but quite a bit of work. Any volunteer ? :-) > > > > Note: after creation of this commit, it was noticed that Steve > > > > Longerbeam has a very similar solution in his fork. > > > > > > > > Fixes: 769afd212b16 ("media: rcar-csi2: add Renesas R-Car MIPI CSI-2 receiver driver") > > > > Cc: Steve Longerbeam > > > > Signed-off-by: Dennis Rachui > > > > --- > > > > drivers/media/platform/rcar-vin/rcar-csi2.c | 21 ++++++++++++++++++++- > > > > 1 file changed, 20 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/media/platform/rcar-vin/rcar-csi2.c b/drivers/media/platform/rcar-vin/rcar-csi2.c > > > > index e28eff0..98152e1 100644 > > > > --- a/drivers/media/platform/rcar-vin/rcar-csi2.c > > > > +++ b/drivers/media/platform/rcar-vin/rcar-csi2.c > > > > @@ -724,18 +724,37 @@ static int rcsi2_set_pad_format(struct v4l2_subdev *sd, > > > > { > > > > struct rcar_csi2 *priv = sd_to_csi2(sd); > > > > struct v4l2_mbus_framefmt *framefmt; > > > > + int ret = 0; > > > > + > > > > + mutex_lock(&priv->lock); > > > > > > > > if (!rcsi2_code_to_fmt(format->format.code)) > > > > format->format.code = rcar_csi2_formats[0].code; > > > > > > > > if (format->which == V4L2_SUBDEV_FORMAT_ACTIVE) { > > > > + > > > > + /* > > > > + * Do not apply changes to active format while streaming. > > > > + * > > > > + * Since video streams could be forwarded from sink pad to any > > > > + * source pad (depending on CSI-2 channel routing), all > > > > + * media pads are effected by this rule. > > > > + */ > > > > + if (priv->stream_count > 0) { > > > > + ret = -EBUSY; > > > > + goto out; > > > > + } > > > > + > > > > priv->mf = format->format; > > > > } else { > > > > framefmt = v4l2_subdev_get_try_format(sd, sd_state, 0); > > > > *framefmt = format->format; > > > > } > > > > > > > > - return 0; > > > > +out: > > > > + mutex_unlock(&priv->lock); > > > > + > > > > + return ret; > > > > } > > > > > > > > static int rcsi2_get_pad_format(struct v4l2_subdev *sd, -- Regards, Laurent Pinchart