From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753575AbdBRSMY (ORCPT ); Sat, 18 Feb 2017 13:12:24 -0500 Received: from pandora.armlinux.org.uk ([78.32.30.218]:48354 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753155AbdBRSMW (ORCPT ); Sat, 18 Feb 2017 13:12:22 -0500 Date: Sat, 18 Feb 2017 18:08:44 +0000 From: Russell King - ARM Linux To: Steve Longerbeam Cc: robh+dt@kernel.org, mark.rutland@arm.com, shawnguo@kernel.org, kernel@pengutronix.de, fabio.estevam@nxp.com, mchehab@kernel.org, hverkuil@xs4all.nl, nick@shmanahar.org, markus.heiser@darmarIT.de, p.zabel@pengutronix.de, laurent.pinchart+renesas@ideasonboard.com, bparrot@ti.com, geert@linux-m68k.org, arnd@arndb.de, sudipm.mukherjee@gmail.com, minghsiu.tsai@mediatek.com, tiffany.lin@mediatek.com, jean-christophe.trotin@st.com, horms+renesas@verge.net.au, niklas.soderlund+renesas@ragnatech.se, robert.jarzmik@free.fr, songjun.wu@microchip.com, andrew-ct.chen@mediatek.com, gregkh@linuxfoundation.org, shuah@kernel.org, sakari.ailus@linux.intel.com, pavel@ucw.cz, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-media@vger.kernel.org, devel@driverdev.osuosl.org Subject: Re: [PATCH v4 29/36] media: imx: mipi-csi2: enable setting and getting of frame rates Message-ID: <20170218180844.GK21222@n2100.armlinux.org.uk> References: <1487211578-11360-1-git-send-email-steve_longerbeam@mentor.com> <1487211578-11360-30-git-send-email-steve_longerbeam@mentor.com> <24d42948-a77d-445f-e3e9-ab595b0cfc3e@gmail.com> <20170218092335.GI21222@n2100.armlinux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Feb 18, 2017 at 09:29:17AM -0800, Steve Longerbeam wrote: > On 02/18/2017 01:23 AM, Russell King - ARM Linux wrote: > >On Fri, Feb 17, 2017 at 05:12:44PM -0800, Steve Longerbeam wrote: > >>Hi Russell, > >> > >>I signed-off on this but after more review I'm not sure this is right. > >> > >>The CSI-2 receiver really has no control over frame rate. It's output > >>frame rate is the same as the rate that is delivered to it. > >> > >>So this subdev should either not implement these ops, or it should > >>refer them to the attached source subdev. > > > >Where in the V4L2 documentation does it say that is permissible? > > > > https://www.linuxtv.org/downloads/v4l-dvb-apis-old/vidioc-subdev-g-frame-interval.html > > "The frame interval only makes sense for sub-devices that can control the > frame period on their own. This includes, for instance, image sensors and TV > tuners. Sub-devices that don't support frame intervals must not implement > these ioctls." That sounds clear - but the TV tuner example seems odd - the frame rate is determined at transmission time, not reception time. Yes, it's possible to skip frames (which would be scaling) but you can't _control_ the frame rate per se. > >If you don't implement these, media-ctl fails to propagate _anything_ > >to the next sink pad if you specify a frame rate, because media-ctl > >throws an error and exits immediately. > > > > But I agree with you here. I think our only option is to ignore that > quoted requirement above and propagate [gs]_frame_interval all the way > to the CSI (which can control the frame rate via frame skipping). Sounds like something to tackle the media maintainers over - the documentation vs media-ctl seem to have different ideas on this point. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.