Re: [PATCH v2] PM / runtime: Rework pm_runtime_force_suspend/resume()

[Geert Uytterhoeven]

Hi Ulf,

On Tue, Jan 9, 2018 at 3:27 PM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
> On 9 January 2018 at 14:37, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
>> On Wed, Jan 3, 2018 at 12:06 PM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
>>> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>>> 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@xxxxxxxxx>
>>
>> This patch causes a regression during system resume on Renesas Salvator-XS
>> with R-Car H3 ES2.0:
>>
>>     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.
>
> What happens if you apply both the revert and the above series?
>
> Does the WARNING still disappear? Or have something else been changed?

The warning doesn't seem to go away in that case.

Although Shimoda-san reported before it does. So something else has changed?

>> 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?
>
> Huh, this seems broken in several aspects.
>
> Could this be the classic case of having the wrong suspend/resume
> order of devices?

Possibly.

/me no USB expert.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds