linux-kernel - Re: [PATCH v1] driver core: Fix suspend/resume order issue with deferred probe

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Message-ID: <CAGETcx-93ps8GFSfY5eeBtxoekB5TtT+HPHV8aVoDLtXz48bVA@mail.gmail.com>
Date:   Thu, 25 Jun 2020 10:02:34 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH v1] driver core: Fix suspend/resume order issue with
 deferred probe

Dropping Feng and Toan due to mail bounces.

On Thu, Jun 25, 2020 at 1:58 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> Hi Saravana,
>
> Thanks for your patch!
>
> On Thu, Jun 25, 2020 at 5:24 AM Saravana Kannan <saravanak@...gle.com> wrote:
> > Under the following conditions:
> > - driver A is built in and can probe device-A
> > - driver B is a module and can probe device-B
>
> I think this is not correct: in my case driver B is builtin, too.

This is a correct example, it just doesn't match with your case :)

Talking about fw_devlink_pause/resume() just distracts from the real
issue that's also present in systems that don't use DT.

You have this problem even on an ACPI system -- distributions loading
all the modules in a PC. We want suspend/resume to work for those too.
So, I'm just going for a simpler example.

> > - device-A is supplier of device-B
> >
> > Without this patch:
> > 1. device-A is added.
> > 2. device-B is added.
> > 3. dpm_list is now [device-A, device-B].
> > 4. driver-A defers probe of device-A.
> > 5. deferred probe of device-A is reattempted
>
> I think this is misleading: in my case driver-A did not defer the probe
> of device-A, and driver-A never returned -EPROBE_DEFER.
> Probing was merely paused, due to fw_devlink_pause();

What I said above. fw_devlink_pause() just defers the probe for the
device -- that's how it pauses and resumes probing. For example,
device link can defer the probe for a device without ever getting to
the driver too.

> > 6. device-A is moved to end of dpm_list.
> > 6. dpm_list is now [device-B, device-A].
> > 7. driver-B is loaded and probes device-B.
> > 8. dpm_list stays as [device-B, device-A].
> >
> > Suspend (which goes in the reverse order of dpm_list) fails because
> > device-A (supplier) is suspended before device-B (consumer).
> >
> > With this patch:
> > 1. device-A is added.
> > 2. device-B is added.
> > 3. dpm_list is now [device-A, device-B].
> > 4. driver-A defers probe of device-A.
> > 5. deferred probe of device-A is reattempted later.
> > 6. dpm_list is now [device-B, device-A].
> > 7. driver-B is loaded and probes device-B.
> > 8. dpm_list is now [device-A, device-B].
> >
> > Suspend works because device-B (consumer) is suspended before device-A
> > (supplier).
> >
> > Fixes: 494fd7b7ad10 ("PM / core: fix deferred probe breaking suspend resume order")
> > Fixes: 716a7a259690 ("driver core: fw_devlink: Add support for batching fwnode parsing")
> > Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
> > Signed-off-by: Saravana Kannan <saravanak@...gle.com>
>
> This fixes wake-up by GPIO key on r8a7740/armadillo and sh73a0/kzm9g.
> Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>

Thanks!

>
> > --- a/drivers/base/dd.c
> > +++ b/drivers/base/dd.c
> > @@ -109,6 +109,8 @@ static void deferred_probe_work_func(struct work_struct *work)
> >                  * probe makes that very unsafe.
> >                  */
> >                 device_pm_move_to_tail(dev);
> > +               /* Greg/Rafael: SHOULD I DELETE THIS? ^^ I think I should, but
> > +                * I'm worried if it'll have some unintended consequeneces. */
>
> Works fine for me with the call to device_pm_move_to_tail() removed, too
> (at least on the two boards that showed the issue before).

Yes, it feels right to remove this, but I just wanted to get a few
more opinions.


-Saravana