linux-kernel - Re: [PATCH/RFC 1/2] PM / wakeup: Add callback for wake-up change notification

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Date:   Mon, 23 Apr 2018 11:32:13 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Marek Vasut <marek.vasut+renesas@...il.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH/RFC 1/2] PM / wakeup: Add callback for wake-up change notification

Hi Rafael,

On Mon, Apr 23, 2018 at 11:18 AM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Wednesday, March 14, 2018 12:26:24 PM CEST Geert Uytterhoeven wrote:
>> Add a callback to inform a device that his wake-up setting has been
>> changed.  This allows a device to synchronize device configuration with
>> an external user action.
>>
>> E.g. on systems using a Rohm BD9571MWV PMIC and a toggle accessory power
>> switch, the system suspend procedure is:
>>   1. Configure PMIC for DDR backup mode, which changes the role of the
>>      accessory power switch from a power to a wake-up switch,
>>   2. Switch accessory power switch off, to prepare for system suspend,
>>   3. Suspend system.
>>
>> Hence step 1 cannot be done in the PMIC's suspend callback,
>
> I don't quite understand this, so can you please explain?
>
> What can't it be done from ->prepare() or even from a suspend notifier?
>
>> but it can be done in the new callback, in response to the user writing "enabled"
>> to the PMIC's wakeup virtual file in sysfs.

Step 2 (flip a switch on the board) is a manual step, to be done by the user.
So it cannot be done from any suspend callback or notifier.

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