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 11:18:17 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     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@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH/RFC 1/2] PM / wakeup: Add callback for wake-up change notification

First, sorry for the huge delay.

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.