Re: [PATCH v3 2/4] mfd: add Gateworks System Controller core driver
From: Mark Brown
Date: Wed Apr 04 2018 - 10:41:51 EST
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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