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

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Date:   Thu, 25 Jun 2020 10:57:52 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>, Toan Le <toanle@....com>,
        Feng Kan <fkan@....com>,
        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

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.

> - 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();

> 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>

> --- 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).

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