From mboxrd@z Thu Jan 1 00:00:00 1970 From: Philipp Zabel Subject: Re: [PATCH v4 29/36] media: imx: mipi-csi2: enable setting and getting of frame rates Date: Mon, 13 Mar 2017 14:55:01 +0100 Message-ID: <1489413301.2288.53.camel@pengutronix.de> References: <1487211578-11360-1-git-send-email-steve_longerbeam@mentor.com> <1487211578-11360-30-git-send-email-steve_longerbeam@mentor.com> <20170220220409.GX16975@valkosipuli.retiisi.org.uk> <20170221001332.GS21222@n2100.armlinux.org.uk> <25596b21-70de-5e46-f149-f9ce3a86ecb7@gmail.com> <1487667023.2331.8.camel@pengutronix.de> <20170313131647.GB10701@valkosipuli.retiisi.org.uk> <20170313132701.GJ21222@n2100.armlinux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20170313132701.GJ21222-l+eeeJia6m9URfEZ8mYm6t73F7V6hmMc@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Russell King - ARM Linux Cc: Sakari Ailus , Steve Longerbeam , robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, mark.rutland-5wv7dgnIgG8@public.gmane.org, shawnguo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, kernel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org, fabio.estevam-3arQi8VN3Tc@public.gmane.org, mchehab-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, hverkuil-qWit8jRvyhVmR6Xm/wNWPw@public.gmane.org, nick-gcszYUEDH4VrovVCs/uTlw@public.gmane.org, markus.heiser-O6JHGLzbNUwb1SvskN2V4Q@public.gmane.org, laurent.pinchart+renesas-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org, bparrot-l0cyMroinI0@public.gmane.org, geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org, arnd-r2nGTMty4D4@public.gmane.org, sudipm.mukherjee-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, minghsiu.tsai-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org, tiffany.lin-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org, jean-christophe.trotin-qxv4g6HH51o@public.gmane.org, horms+renesas-/R6kz+dDXgpPR4JQBCEnsQ@public.gmane.org, niklas.soderlund+renesas-1zkq55x86MTxsAP9Fp7wbw@public.gmane.org, robert.jarzmik-GANU6spQydw@public.gmane.org, songjun.wu-UWL1GkI3JZL3oGB3hsPCZA@public.gmane.org, andrew-ct.chen-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org, gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org, shuah-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, sakari.ailus-VuQAYsv1563Yd54FQh9/CA@public.gmane.org, pavel-+ZI9xUNit7I@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-a List-Id: devicetree@vger.kernel.org On Mon, 2017-03-13 at 13:27 +0000, Russell King - ARM Linux wrote: > On Mon, Mar 13, 2017 at 03:16:48PM +0200, Sakari Ailus wrote: > > The vast majority of existing drivers do not implement them nor the user > > space expects having to set them. Making that mandatory would break existing > > user space. > > > > In addition, that does not belong to link validation either: link validation > > should only include static properties of the link that are required for > > correct hardware operation. Frame rate is not such property: hardware that > > supports the MC interface generally does not recognise such concept (with > > the exception of some sensors). Additionally, it is dynamic: the frame rate > > can change during streaming, making its validation at streamon time useless. > > So how do we configure the CSI, which can do frame skipping? > > With what you're proposing, it means it's possible to configure the > camera sensor source pad to do 50fps. Configure the CSI sink pad to > an arbitary value, such as 30fps, and configure the CSI source pad to > 15fps. > > What you actually get out of the CSI is 25fps, which bears very little > with the actual values used on the CSI source pad. > > You could say "CSI should ask the camera sensor" - well, that's fine > if it's immediately downstream, but otherwise we'd need to go walking > down the graph to find something that resembles its source - there may > be mux and CSI2 interface subdev blocks in that path. Or we just accept > that frame rates are completely arbitary and bear no useful meaning what > so ever. Which would include the frame interval returned by VIDIOC_G_PARM on the connected video device, as that gets its information from the CSI output pad's frame interval. regards Philipp -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html