linux-kernel - Re: power supply gating with ltc2978

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Message-ID: <alpine.DEB.2.02.1408190914310.22837@atx-linux-37>
Date:	Tue, 19 Aug 2014 09:21:36 -0500
From:	atull <atull@...nsource.altera.com>
To:	Guenter Roeck <linux@...ck-us.net>
CC:	Mark Brown <broonie@...nel.org>, Jean Delvare <jdelvare@...e.de>,
	<lm-sensors@...sensors.org>, <linux-kernel@...r.kernel.org>,
	Liam Girdwood <lgirdwood@...il.com>
Subject: Re: power supply gating with ltc2978

On Mon, 18 Aug 2014, Guenter Roeck wrote:

> On Sat, Aug 16, 2014 at 02:20:50PM +0100, Mark Brown wrote:
> > On Fri, Aug 15, 2014 at 04:34:49PM -0500, atull wrote:
> > 
> > > I am interested in adding functionality to be able to gate power supplies 
> > > going through a ltc2978.  I see that there is a hwmon driver already 
> > > existing (hwmon/pmbus/ltc2978.c).  I see some of the other hwmon drivers 
> > > have MFD's.  It looks like this ltc driver would need a MFD and a 
> > > regulator driver added.  However I don't see other pmbus hwmon drivers
> > > using MFD.
> > 
> > > So I am asking for recommendations and reservations on how to proceed here 
> > > before I get too far with this.
> > 
> > Without knowing anything at all about pmbus or this particular hardware
> > it's hard to comment but what you're saying here sounds sensible (though
> > I do see that apparently splitting the drivers may not actually be
> > sensible from Guenter's followup).
> 
> I had originally thought about converting the pmbus drivers to mfd with client
> drivers, but I concluded that it would add a lot of complexity with little gain.
> It makes sense to separate a driver into mfd and a number of client drivers
> if a device has clear functional blocks for the different devices it supports.
> With PMBus, this is not the case. Separating a PMBus driver would be a purely
> artificial costruct, and there would be overlapping functionality. Separating
> just a single driver out of the group of PMBus drivers, as seems to be suggested
> above, makes even less sense as one simply can not separate the core PMBus
> driver code from its front-end drivers.
> 
> On the other side, adding regulator support into the PMBus driver code would
> make a lot of sense. It should also be quite straightforward.
> 
> Or anyway that is my opinion. If someone wants to spend the time and separate
> the PMBus drivers into an MfD part and hwmon and regulator client drivers, I'll
> be happy to look at the resulting patch set.
> 
> Guenter
> 

Hi Guenter,

I'd really rather just add regulator support to the PMBus driver code and 
avoid all the mess of creating a MFD.  It seems more straigtforward. I'll 
let you know when I have something working to look at.

Alan
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