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

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Date:   Tue, 28 Nov 2017 12:48:00 +0000
From:   Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
CC:     Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.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()

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.

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.

Best regards,
Yoshihiro Shimoda