linux-kernel - Re: [PATCH v3 2/4] mfd: add Gateworks System Controller core driver

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Date:   Wed, 4 Apr 2018 15:41:19 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Tim Harvey <tharvey@...eworks.com>,
        Lee Jones <lee.jones@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Wim Van Sebroeck <wim@...ana.be>,
        Guenter Roeck <linux@...ck-us.net>,
        linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
        linux-watchdog@...r.kernel.org,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 2/4] mfd: add Gateworks System Controller core driver

On Wed, Apr 04, 2018 at 03:12:39PM +0200, Andrew Lunn wrote:
> > What about the 'reset' functionality? Is there something in the power
> > supply API for hooking in a GPIO based power switch (in my case it
> > would be i2c) as I would think that would be common for ATX supplies?
> > I didn't see anything in Documentation/power.

> > This is what led me to the restart handler idea. Ultimately when
> > someone issues a 'reboot' I would like it to use the GSC to
> > power-cycle the board.

> I think you end up with the same problem. By the time you need to turn
> the power supply off, too much of the kernel is shut down to be able
> to use I2C. And if you are in the middle of an Oops, you have no idea
> of the current state. Another I2C transaction could be under way etc.
> All the current reset drivers are pretty much self contained, atomic
> and use KISS hardware like a GPIO.

> Maybe you best bet is to see if you can find any other I2C PMICs which
> the kernel supports.

Most systems have a handshake for final power down via asserting signals
rather than using register writes, the final power down sequence usually
runs way after software.  There's a few things that don't which just
unceremoniously cut the power earlier on without completing the full
power down sequence which for all practical purposes mostly works.

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