04.10.2021 14:01, Ulf Hansson пишет: > On Fri, 1 Oct 2021 at 21:00, Dmitry Osipenko <digetx@xxxxxxxxx> wrote: >> >> 01.10.2021 17:55, Ulf Hansson пишет: >>> On Fri, 1 Oct 2021 at 16:29, Dmitry Osipenko <digetx@xxxxxxxxx> wrote: >>>> >>>> 01.10.2021 16:39, Ulf Hansson пишет: >>>>> On Mon, 27 Sept 2021 at 00:42, Dmitry Osipenko <digetx@xxxxxxxxx> wrote: >>>>>> >>>>>> Add runtime power management and support generic power domains. >>>>>> >>>>>> Tested-by: Peter Geis <pgwipeout@xxxxxxxxx> # Ouya T30 >>>>>> Tested-by: Paul Fertser <fercerpav@xxxxxxxxx> # PAZ00 T20 >>>>>> Tested-by: Nicolas Chauvet <kwizart@xxxxxxxxx> # PAZ00 T20 and TK1 T124 >>>>>> Tested-by: Matt Merhar <mattmerhar@xxxxxxxxxxxxxx> # Ouya T30 >>>>>> Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx> >>>>>> --- >>>>>> drivers/gpu/drm/tegra/gr2d.c | 155 +++++++++++++++++++++++++++++++++-- >>>>> >>>>> [...] >>>>> >>>>>> static int gr2d_remove(struct platform_device *pdev) >>>>>> @@ -259,15 +312,101 @@ static int gr2d_remove(struct platform_device *pdev) >>>>>> return err; >>>>>> } >>>>>> >>>>>> + pm_runtime_dont_use_autosuspend(&pdev->dev); >>>>>> + pm_runtime_disable(&pdev->dev); >>>>> >>>>> There is no guarantee that the ->runtime_suspend() has been invoked >>>>> here, which means that clock may be left prepared/enabled beyond this >>>>> point. >>>>> >>>>> I suggest you call pm_runtime_force_suspend(), instead of >>>>> pm_runtime_disable(), to make sure that gets done. >>>> >>>> The pm_runtime_disable() performs the final synchronization, please see [1]. >>>> >>>> [1] >>>> https://elixir.bootlin.com/linux/v5.15-rc3/source/drivers/base/power/runtime.c#L1412 >>> >>> pm_runtime_disable() end up calling _pm_runtime_barrier(), which calls >>> cancel_work_sync() if dev->power.request_pending has been set. >>> >>> If the work that was punted to the pm_wq in rpm_idle() has not been >>> started yet, we end up just canceling it. In other words, there are no >>> guarantees it runs to completion. >> >> You're right. Although, in a case of this particular patch, the syncing >> is actually implicitly done by pm_runtime_dont_use_autosuspend(). >> >> But for drivers which don't use auto-suspend, there is no sync. This >> looks like a disaster, it's a very common pattern for drivers to >> 'put+disable'. >> >>> Moreover, use space may have bumped the usage count via sysfs for the >>> device (pm_runtime_forbid()) to keep the device runtime resumed. >> >> Right, this is also a disaster in a case of driver removal. >> >>>> Calling pm_runtime_force_suspend() isn't correct because each 'enable' >>>> must have the corresponding 'disable'. Hence there is no problem here. >>> >>> pm_runtime_force_suspend() calls pm_runtime_disable(), so I think that >>> should be fine. No? >> >> [adding Rafael] >> >> Rafael, could you please explain how drivers are supposed to properly >> suspend and disable RPM to cut off power and reset state that was >> altered by the driver's resume callback? What we're missing? Is Ulf's >> suggestion acceptable? >> >> The RPM state of a device is getting reset on driver's removal, hence >> all refcounts that were bumped by the rpm-resume callback of the device >> driver will be screwed up if device is kept resumed after removal. I >> just verified that it's true in practice. > > Note that, what makes the Tegra drivers a bit special is that they are > always built with CONFIG_PM being set (selected from the "SoC" > Kconfig). > > Therefore, pm_runtime_force_suspend() can work for some of these > cases. Using this, would potentially avoid the driver from having to > runtime resume the device in ->remove(), according to the below > generic sequence, which is used in many drivers. > > pm_runtime_get_sync() > clk_disable_unprepare() (+ additional things to turn off the device) > pm_runtime_disable() > pm_runtime_put_noidle() It's not a problem to change this patchset. The problem is that if you'll grep mainline for 'pm_runtime_disable', you will find that there are a lot of drivers in a potential trouble. I'm proposing that we should change pm_runtime_disable() to perform the syncing with this oneliner: diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c index ec94049442b9..5c9f28165824 100644 --- a/drivers/base/power/runtime.c +++ b/drivers/base/power/runtime.c @@ -1380,6 +1380,8 @@ EXPORT_SYMBOL_GPL(pm_runtime_barrier); */ void __pm_runtime_disable(struct device *dev, bool check_resume) { + flush_work(&dev->power.work); + spin_lock_irq(&dev->power.lock); if (dev->power.disable_depth > 0) { Objections? The sysfs rpm-forbid is a separate problem and it's less troublesome since it requires root privileges. It's also not something that userspace touches casually. For now I don't know what could be done about it.
