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

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Date:   Tue, 9 Jan 2018 14:37:44 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
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>
Subject: Re: [PATCH v2] PM / runtime: Rework pm_runtime_force_suspend/resume()

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:

    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.

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?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

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