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

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Message-ID: <CAJZ5v0jOk0pLegJK0-LwK3WEA5A560eNd32O5jK+PzQL9ZRofA@mail.gmail.com>
Date:   Mon, 23 Apr 2018 11:37:35 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        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

On Mon, Apr 23, 2018 at 11:32 AM, Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> 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.

I still find it somewhat difficult to follow you here. :-)

How is this expected to work?  Is the user expected to flip the switch
on the board and then write to "wakeup" or is that the other way
around?