From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Osipenko Subject: Re: [PATCH v2 1/2] i2c: tegra: Better handle case where CPU0 is busy for a long time Date: Wed, 29 Apr 2020 17:46:46 +0300 Message-ID: <5863e364-480e-7839-c42b-73a7f6990a30@gmail.com> References: <79f6560e-dbb5-0ae1-49f8-cf1cd95396ec@nvidia.com> <20200427074837.GC3451400@ulmo> <20200427110033.GC3464906@ulmo> <3a06811c-02dc-ce72-ebef-78c3fc3f4f7c@gmail.com> <20200427151234.GE3464906@ulmo> <1ab276cf-c2b0-e085-49d8-b8ce3dba8fbe@gmail.com> <20200429081448.GA2345465@ulmo> <20200429085502.GB2345465@ulmo> <9e36c4ec-ca02-bd15-d765-15635f09db4b@gmail.com> <7442f4cd-6406-41f6-5c9b-932bff8ad5b2@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <7442f4cd-6406-41f6-5c9b-932bff8ad5b2-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> Content-Language: en-US Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Jon Hunter , Thierry Reding Cc: Wolfram Sang , Laxman Dewangan , Manikanta Maddireddy , Vidya Sagar , linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-tegra@vger.kernel.org 29.04.2020 16:57, Jon Hunter пишет: > > On 29/04/2020 13:35, Dmitry Osipenko wrote: >> 29.04.2020 11:55, Thierry Reding пишет: >> ... >>>>> It's not "papering over an issue". The bug can't be fixed properly >>>>> without introducing I2C atomic transfers support for a late suspend >>>>> phase, I don't see any other solutions for now. Stable kernels do not >>>>> support atomic transfers at all, that proper solution won't be backportable. >>>> >>>> Hm... on a hunch I tried something and, lo and behold, it worked. I can >>>> get Cardhu to properly suspend/resume on top of v5.7-rc3 with the >>>> following sequence: >>>> >>>> revert 9f42de8d4ec2 i2c: tegra: Fix suspending in active runtime PM state >>>> apply http://patchwork.ozlabs.org/project/linux-tegra/patch/20191213134417.222720-1-thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org/ >>>> >>>> I also ran that through our test farm and I don't see any other issues. >>>> At the time I was already skeptical about pm_runtime_force_suspend() and >>>> pm_runtime_force_resume() and while I'm not fully certain why exactly it >>>> doesn't work, the above on top of v5.7-rc3 seems like a good option. >>>> >>>> I'll try to do some digging if I can find out why exactly force suspend >>>> and resume doesn't work. >>> >>> Ah... so it looks like pm_runtime_force_resume() never actually does >>> anything in this case and then disable_depth remains at 1 and the first >>> tegra_i2c_xfer() will then fail to runtime resume the controller. >> >> That's the exactly expected behaviour of the RPM force suspend/resume. >> The only unexpected part for me is that the tegra_i2c_xfer() runtime >> resume then fails in the NOIRQ phase. > > From reading the changelog for commit 1e2ef05bb8cf ("PM: Limit race > conditions between runtime PM and system sleep (v2))", this is the > expected behaviour for runtime resume in the noirq phase. I'm curious whether there is a way to tell RPM that it's okay to do it for a particular device, like I2C that uses IRQ-safe RPM + doesn't have parent devices that need to be resumed.