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

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Message-ID: <TY1PR06MB0992899AE427576E3F83CF54D83B0@TY1PR06MB0992.apcprd06.prod.outlook.com>
Date:   Wed, 29 Nov 2017 08:21:22 +0000
From:   Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
To:     Alan Stern <stern@...land.harvard.edu>
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>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        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,

> From: Alan Stern, Sent: Wednesday, November 29, 2017 12:07 AM
> 
> On Tue, 28 Nov 2017, Yoshihiro Shimoda 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>
<snip>
> > > 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.

I'm so sorry, but this is mistake.
The renesas_usbhs doesn't use the phy_rcar_gen3_usb2 driver.
So,

> > --> 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.)

They are also mistake.

> > I'll continue to investigate this issue tomorrow.
> 
> Does the phy_rcar_gen3_usb2 driver use runtime PM?

Yes, the phy_rcar_gen3_usb2 uses runtime PM.

>  It looks like the
> phy device somehow gets enabled for runtime PM when it shouldn't be.

I also think that now.
I don't find why for now, but the usage_count of a phy device was not 1 just before suspend.
(This "a phy device" means the child of ee0a0200.usb-phy device.)

> (And by the way, what device is the child of ee0a0200.usb-phy?)

It's a phy device:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/phy/phy-core.c?h=v4.15-rc1#n773

Best regards,
Yoshihiro Shimoda

> Alan Stern