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

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Date:   Tue, 9 Jan 2018 16:00:35 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        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>
Subject: Re: [PATCH v2] PM / runtime: Rework pm_runtime_force_suspend/resume()

On Tue, Jan 9, 2018 at 2:37 PM, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> Hi Rafael,
>
> 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.

Thanks,
Rafael