Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935416AbdCLUgn (ORCPT ); Sun, 12 Mar 2017 16:36:43 -0400 Received: from mail-pg0-f65.google.com ([74.125.83.65]:33698 "EHLO mail-pg0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934692AbdCLUgh (ORCPT ); Sun, 12 Mar 2017 16:36:37 -0400 Subject: Re: [PATCH v5 00/39] i.MX Media Driver To: Russell King - ARM Linux References: <1489121599-23206-1-git-send-email-steve_longerbeam@mentor.com> <20170312175118.GP21222@n2100.armlinux.org.uk> <191ef88d-2925-2264-6c77-46647394fc72@gmail.com> <20170312192932.GQ21222@n2100.armlinux.org.uk> <58b30bca-20ca-d4bd-7b86-04a4b8e71935@gmail.com> Cc: mark.rutland@arm.com, andrew-ct.chen@mediatek.com, minghsiu.tsai@mediatek.com, sakari.ailus@linux.intel.com, nick@shmanahar.org, songjun.wu@microchip.com, hverkuil@xs4all.nl, Steve Longerbeam , pavel@ucw.cz, robert.jarzmik@free.fr, devel@driverdev.osuosl.org, markus.heiser@darmarIT.de, laurent.pinchart+renesas@ideasonboard.com, shuah@kernel.org, geert@linux-m68k.org, linux-media@vger.kernel.org, devicetree@vger.kernel.org, kernel@pengutronix.de, arnd@arndb.de, mchehab@kernel.org, bparrot@ti.com, robh+dt@kernel.org, horms+renesas@verge.net.au, tiffany.lin@mediatek.com, linux-arm-kernel@lists.infradead.org, niklas.soderlund+renesas@ragnatech.se, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, jean-christophe.trotin@st.com, p.zabel@pengutronix.de, fabio.estevam@nxp.com, shawnguo@kernel.org, sudipm.mukherjee@gmail.com From: Steve Longerbeam Message-ID: Date: Sun, 12 Mar 2017 13:36:32 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2535 Lines: 59 On 03/12/2017 01:16 PM, Steve Longerbeam wrote: > > > On 03/12/2017 12:44 PM, Steve Longerbeam wrote: >> >> >> On 03/12/2017 12:29 PM, Russell King - ARM Linux wrote: >>> On Sun, Mar 12, 2017 at 12:21:45PM -0700, Steve Longerbeam wrote: >>>> There's actually nothing preventing userland from disabling a link >>>> multiple times, and imx_media_link_notify() complies, and so >>>> csi_s_power(OFF) gets called multiple times, and so that WARN_ON() >>>> in there is silly, I borrowed this from other MC driver examples, >>>> but it makes no sense to me, I'll remove it and prevent the power >>>> count from going negative. >>> >>> Hmm. So what happens if one of the CSI's links is enabled, and we >>> disable a different link from the CSI several times? Doesn't that >>> mean the power count will go to zero despite there being an enabled >>> link? >> >> Yes, the CSI will be powered off even if it still has an enabled link. >> But one of its other links has been disabled, meaning the pipeline as >> a whole is disabled. So I think it makes sense to power down the CSI, >> the pipeline isn't usable at that point. >> >> And remember that the CSI does not allow both output pads to be enabled >> at the same time. If that were so then indeed there would be a problem, >> because it would mean there is another active pipeline that requires the >> CSI being powered on, but that's not the case. >> >> I think this is consistent with the other entities as well, but I will >> double check. > > > At first I thought this could be a problem for one entity, the csi-2 > receiver. > > It can enable all four of its output pads at once (if the input stream > contains all 4 virtual channels, the csi-2 receiver must support > demuxing all of them onto all 4 of its output pads). > > But after more review, this should not be an issue. If a csi-2 sink > (a CSI or a CSI mux) link is disabled, the csi-2 receiver is no longer > reachable from that sink, so attempts to disable the csi-2 via that > path again is not possible. The other potential problem is disabling > from the csi-2's own sink pad, but in that case the csi-2 no longer > has a source, so again it makes sense to power off the csi-2 even > if it has enabled output pads. > But hold on, if my logic is correct, then why did the CSI power-off get reached in your case, multiple times? Yes I think there is a bug, link_notify() is not checking if the link has already been disabled. I will fix this. But I'm surprised media core's link_notify handling doesn't do this. Steve