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@xxxxxxxxx/ >>>> >>>> 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.
