netdev - Re: [PATCH] net: smsc911x: Synchronize the runtime PM status during system suspend

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Message-ID: <CAMuHMdUbU07t2kB6J0rSOiOTbDkegP73FAAEenViuDjQUFE-Jg@mail.gmail.com>
Date:   Thu, 27 Oct 2016 13:41:14 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Alan Stern <stern@...land.harvard.edu>,
        Linux PM list <linux-pm@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Kevin Hilman <khilman@...nel.org>,
        Lina Iyer <lina.iyer@...aro.org>,
        Jon Hunter <jonathanh@...dia.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Steve Glendinning <steve.glendinning@...well.net>
Subject: Re: [PATCH] net: smsc911x: Synchronize the runtime PM status during
 system suspend

Hi Ulf,

On Thu, Oct 27, 2016 at 1:23 PM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> The smsc911c driver puts its device into low power state when entering
> system suspend. Although it doesn't update the device's runtime PM status
> to RPM_SUSPENDED, which causes problems for a parent device.
>
> In particular, when the runtime PM status of the parent is requested to be
> updated to RPM_SUSPENDED, the runtime PM core prevent this, because it's
> forbidden to runtime suspend a device, which has an active child.
>
> Fix this by updating the runtime PM status of the smsc911x device to
> RPM_SUSPENDED during system suspend. In system resume, let's reverse that
> action by runtime resuming the device and thus also the parent.

Thanks for your patch!

The changelog sounds quite innocent, but this does fix a system crash
during resume from s2ram.

> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Cc: Steve Glendinning <steve.glendinning@...well.net>
> Fixes: 8b1107b85efd ("PM / Runtime: Don't allow to suspend a device with an active child")

While the abovementioned commit made the problem visible, the root cause
was present before, right?

> ---
>
> Note that the commit this change fixes is currently queued for 4.10 via
> Rafael's linux-pm tree. So this fix should go via that tree as well.

Alternatively, this could go in in v4.9 to avoid the problem from ever
appearing in upstream?

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