linux-kernel - Re: [PATCH] PM / runtime: Drop children check from __pm_runtime_set

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Date:   Tue, 28 Nov 2017 18:22:56 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        USB list <linux-usb@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH] PM / runtime: Drop children check from __pm_runtime_set_status()

On 28 November 2017 at 13:48, Yoshihiro Shimoda
<yoshihiro.shimoda.uh@...esas.com> wrote:
> Hi Geert-san,
>
>> From: Geert Uytterhoeven, Sent: Tuesday, November 28, 2017 7:58 PM
>>
>> Hi Rafael, Shimoda-san,
>>
>> On Sun, Nov 12, 2017 at 1:27 AM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>> >
>> > The check for "active" children in __pm_runtime_set_status(), when
>> > trying to set the parent device status to "suspended", doesn't
>> > really make sense, because in fact it is not invalid to set the
>> > status of a device with runtime PM disabled to "suspended" in any
>> > case.  It is invalid to enable runtime PM for a device with its
>> > status set to "suspended" while its child_count reference counter
>> > is nonzero, but the check in __pm_runtime_set_status() doesn't
>> > really cover that situation.
>> >
>> > For this reason, drop the children check from __pm_runtime_set_status()
>> > and add a check against child_count reference counters of "suspended"
>> > devices to pm_runtime_enable().
>> >
>> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>> > ---
>> >  drivers/base/power/runtime.c |   30 ++++++++++--------------------
>> >  1 file changed, 10 insertions(+), 20 deletions(-)
>> >
>> > Index: linux-pm/drivers/base/power/runtime.c
>> > ===================================================================
>> > --- linux-pm.orig/drivers/base/power/runtime.c
>> > +++ linux-pm/drivers/base/power/runtime.c
>> > @@ -1101,29 +1101,13 @@ int __pm_runtime_set_status(struct devic
>> >                 goto out;
>> >         }
>> >
>> > -       if (dev->power.runtime_status == status)
>> > +       if (dev->power.runtime_status == status || !parent)
>> >                 goto out_set;
>> >
>> >         if (status == RPM_SUSPENDED) {
>> > -               /*
>> > -                * It is invalid to suspend a device with an active child,
>> > -                * unless it has been set to ignore its children.
>> > -                */
>> > -               if (!dev->power.ignore_children &&
>> > -                       atomic_read(&dev->power.child_count)) {
>> > -                       dev_err(dev, "runtime PM trying to suspend device but active child\n");
>>
>> JFTR, this triggered before during system resume on e.g. Salvator-XS with
>> R-Car H3:
>>
>>     ohci-platform ee080000.usb: runtime PM trying to suspend device
>> but active child
>>     phy_rcar_gen3_usb2 ee080200.usb-phy: runtime PM trying to suspend
>> device but active child
>>     ohci-platform ee0c0000.usb: runtime PM trying to suspend device
>> but active child
>>     ohci-platform ee0a0000.usb: runtime PM trying to suspend device
>> but active child
>>     phy_rcar_gen3_usb2 ee0c0200.usb-phy: runtime PM trying to suspend
>> device but active child
>>     phy_rcar_gen3_usb2 ee0a0200.usb-phy: runtime PM trying to suspend
>> device but active child
>>
>> so this was an existing issue with USB before.
>
> Thank you for the report!
> I know that, but since this didn't cause any trouble until now,
> I postponed to investigate the issue... But, I investigate it today.
> I don't find the root cause yet. However, it seems related to usb host and/or usb core.
> --> USB host related devices' child_count will be 1 in suspend timing.
>  --> I guess remote wakeup feature is enabled? But, I don't find the point yet.

I am guessing the issue is triggered by genpd in the suspend noirq
phase (genpd_suspend_noirq()). In there,  there is a call to
pm_runtime_force_suspend() (which calls pm_runtime_set_suspended() and
which triggered the earlier error messages being printed).

The reason why genpd calls pm_runtime_force_suspend(), is because when
validating wakeup configurations for the device "if
(dev->power.wakeup_path && genpd_is_active_wakeup(genpd))", it's
thinks wakeup isn't configured while it probably should be.

An additional note, only when genpd has the GENPD_FLAG_PM_CLK set,
which makes the genpd->dev_ops.stop|start() being assigned, genpd
calls pm_runtime_force_suspend() - else it doesn't.

Perhaps try out the series I recently posted improving the code
dealing with wakeups in genpd and the PM core:
https://www.spinics.net/lists/linux-renesas-soc/msg20122.html
To that, you need to set the new flag (invented in the above series)
DPM_FLAG_IN_BAND_WAKEUP in the driver that configures wakeup of its
device.

Hope this helps!

>
> The renesas_usbhs also uses the phy_rcar_gen3_usb2 driver.
> --> If I only used the renesas_usbhs driver (in other words, I don't install
>     [eo]hci-{hcd,platform} drivers), the issue disappeared.
>  --> So, I think the phy_rcar_gen3_usb2 driver doesn't cause this issue.
>     (But, it is possible to be related though.)
>
> I'll continue to investigate this issue tomorrow.

Please keep me posted, I am interested about the why the problem exists. :-)

Kind regards
Uffe