linux-kernel - Re: [PATCH v2] PM / runtime: Rework pm_runtime_force

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Message-ID: <5304989.KijCPkYIym@aspire.rjw.lan>
Date:   Fri, 12 Jan 2018 13:09:56 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        Kevin Hilman <khilman@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Lukas Wunner <lukas@...ner.de>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>
Subject: Re: [PATCH v2] PM / runtime: Rework pm_runtime_force_suspend/resume()

On Friday, January 12, 2018 12:26:56 PM CET Geert Uytterhoeven wrote:
> Hi Rafael,
> 
> On Tue, Jan 9, 2018 at 5:28 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > On Tuesday, January 9, 2018 5:03:18 PM CET Rafael J. Wysocki wrote:
> >> On Tue, Jan 9, 2018 at 4:30 PM, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> >> > On Tue, Jan 9, 2018 at 4:00 PM, Rafael J. Wysocki <rafael@...nel.org> wrote:
> >> >> On Tue, Jan 9, 2018 at 2:37 PM, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> >> >>> On Wed, Jan 3, 2018 at 12:06 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> >> >>>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >> >>>>
> >> >>>> One of the limitations of pm_runtime_force_suspend/resume() is that
> >> >>>> if a parent driver wants to use these functions, all of its child
> >> >>>> drivers have to do that too because of the parent usage counter
> >> >>>> manipulations necessary to get the correct state of the parent during
> >> >>>> system-wide transitions to the working state (system resume).
> >> >>>> However, that limitation turns out to be artificial, so remove it.
> >> >>>>
> >> >>>> Namely, pm_runtime_force_suspend() only needs to update the children
> >> >>>> counter of its parent (if there's is a parent) when the device can
> >> >>>> stay in suspend after the subsequent system resume transition, as
> >> >>>> that counter is correct already otherwise.  Now, if the parent's
> >> >>>> children counter is not updated, it is not necessary to increment
> >> >>>> the parent's usage counter in that case any more, as long as the
> >> >>>> children counters of devices are checked along with their usage
> >> >>>> counters in order to decide whether or not the devices may be left
> >> >>>> in suspend after the subsequent system resume transition.
> >> >>>>
> >> >>>> Accordingly, modify pm_runtime_force_suspend() to only call
> >> >>>> pm_runtime_set_suspended() for devices whose usage and children
> >> >>>> counters are at the "no references" level (the runtime PM status
> >> >>>> of the device needs to be updated to "suspended" anyway in case
> >> >>>> this function is called once again for the same device during the
> >> >>>> transition under way), drop the parent usage counter incrementation
> >> >>>> from it and update pm_runtime_force_resume() to compensate for these
> >> >>>> changes.
> >> >>>>
> >> >>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >> >>>
> >> >>> This patch causes a regression during system resume on Renesas Salvator-XS
> >> >>> with R-Car H3 ES2.0:
> >> >>
> >> >> I have dropped it for now, but we need to address the underlying issue.
> >> >>
> >> >>>     SError Interrupt on CPU3, code 0xbf000002 -- SError
> >> >>>     SError Interrupt on CPU2, code 0xbf000002 -- SError
> >> >>>     CPU: 3 PID: 1769 Comm: kworker/u16:13 Not tainted
> >> >>> 4.15.0-rc7-arm64-renesas-05338-gf14cf570a813c9ca-dirty #97
> >> >>>     CPU: 2 PID: 1774 Comm: kworker/u16:18 Not tainted
> >> >>> 4.15.0-rc7-arm64-renesas-05338-gf14cf570a813c9ca-dirty #97
> >> >>>     Hardware name: Renesas Salvator-X 2nd version board based on
> >> >>> r8a7795 ES2.0+ (DT)
> >> >>>     Hardware name: Renesas Salvator-X 2nd version board based on
> >> >>> r8a7795 ES2.0+ (DT)
> >> >>>     Workqueue: events_unbound async_run_entry_fn
> >> >>>     Workqueue: events_unbound async_run_entry_fn
> >> >>>     pstate: 60000005 (nZCv daif -PAN -UAO)
> >> >>>     pstate: 60000005 (nZCv daif -PAN -UAO)
> >> >>>     pc : rcar_gen3_phy_usb2_init+0x34/0xf8
> >> >>>     pc : rcar_gen3_phy_usb2_init+0x34/0xf8
> >> >>>     lr : phy_init+0x64/0xcc
> >> >>>     lr : phy_init+0x64/0xcc
> >> >>>     ...
> >> >>>     Kernel panic - not syncing: Asynchronous SError Interrupt
> >> >>>
> >> >>> Note that before, it printed a warning instead:
> >> >>>
> >> >>>     Enabling runtime PM for inactive device (ee0a0200.usb-phy) with
> >> >>> active children
> >> >>>     WARNING: CPU: 0 PID: 1741 at drivers/base/power/runtime.c:1300
> >> >>> pm_runtime_enable+0x94/0xd8
> >> >>>
> >> >>> Reverting commit 0408584d580d4a2c ("PM / runtime: Rework
> >> >>> pm_runtime_force_suspend/resume()") fixes the crash.
> >> >>>
> >> >>> Note that applying Ulf's "[PATCH v2 0/3] phy: core: Re-work runtime PM
> >> >>> deployment and fix an issue"
> >> >>> (https://www.spinics.net/lists/linux-renesas-soc/msg21719.html) instead
> >> >>> does not fix the crash.
> >> >>
> >> >> OK
> >> >>
> >> >>> With more debug code added, it seems the EHCI module clocks (701-703) are
> >> >>> enabled earlier than before. I guess this triggers the workqueue to perform
> >> >>> an operation while another related device (HSUSB 704?) is still disabled?
> >> >>
> >> >> Probably.
> >> >>
> >> >> Likely a device that wasn't resumed before resumes now and that causes
> >> >> the issue to appear.
> >> >>
> >> >> I'm wondering if adding the ignore_children check to the patch helps.
> >> >> If not, there clearly is a resume ordering issue that is papered over
> >> >> by the current code.
> >> >
> >> > Something fishy is going on. Status of the USB PHYs differ before/after
> >> > system suspend, according to /sys/kernel/debug/pm_genpd/pm_genpd_summary:
> >> >
> >> > -    /devices/platform/soc/ee0a0200.usb-phy              active
> >> > -    /devices/platform/soc/ee0c0200.usb-phy              active
> >> > -    /devices/platform/soc/ee080200.usb-phy              active
> >> > +    /devices/platform/soc/ee0a0200.usb-phy              suspended
> >> > +    /devices/platform/soc/ee0c0200.usb-phy              suspended
> >> > +    /devices/platform/soc/ee080200.usb-phy              suspended
> >>
> >> Yeah.
> >>
> >> That's because of the pm_runtime_force_suspend/resume() called by
> >> genpd.  These functions generally may cause devices active before
> >> system suspend to be left in suspend after it.  That generally is a
> >> good idea if the device was not really in use before the system
> >> suspend, but there is a problem that the driver of it may not be
> >> prepared for that to happen (and also the way to determine the "not
> >> really in use" case may not be as expected by the driver).
> >
> > So below is something to try (untested).
> >
> > I know that Ulf will be protesting, but that's what I would do unless there
> > are really *really* good reasons not to.
> 
> With the below, the issue is gone,

Cool, thanks for testing!

> both with and without the dev->power.ignore_children check.

Yes, that check is irrelevant here.

Thanks,
Rafael