linux-kernel - Re: [PATCH V3 2/4] regulator: tps62360: add dt support

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Message-ID: <20120511213001.GD29835@opensource.wolfsonmicro.com>
Date:	Fri, 11 May 2012 22:30:02 +0100
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Laxman Dewangan <ldewangan@...dia.com>
Cc:	"grant.likely@...retlab.ca" <grant.likely@...retlab.ca>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"lrg@...com" <lrg@...com>, Stephen Warren <swarren@...dia.com>,
	"olof@...om.net" <olof@...om.net>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH V3 2/4] regulator: tps62360: add dt support

On Fri, May 11, 2012 at 09:05:01PM +0530, Laxman Dewangan wrote:

> Yaah, I think this flag can map directly to REGULATOR_MODE_FAST. If
> I understand PWM mode properly then this is used when high current
> load is require or fast switching on  load current is require. By
> enabling force PWM enable, hw will not switch to PFM mode based on
> load current.

> I think if we map the regulator mode to FAST as the force PWM enable
> and NORMAL as force PWM =0 then it will be generic.

Yes, this is pretty much exactly what _FAST means.  With modern hardware
the forced PWM mode just isn't needed, a modern regulator is able to
respond sufficiently quickly to changes in the output load.  Mode
switching from software was generally found to be impractical for DCDC
convertors as the load requirements change so quickly and without
software control that by the time you respond from software you can't
switch out of a lower power mode into a higher current one it's too late.

> >>+- ti,enable-vout-discharge: Enable output discharge. This is boolean value.
> >This I think we should definitely add a framework feature for this and
> >make into a generic property, it's a very standard feature and more
> >normally set unconditionally.

> I think this is not require to enable always otherwise there may be
> power dissipation from this path always, just when we off the rail
> (disable rail or when go to shutdown so that the voltage output can
> go down faster).
> Should we add "unsigned en_discharge:1" in regulator init data but
> did not get how core driver can use this flag specially when
> shutdown?

Oh, now you say this I think I remember discussing this with you before!
This is pretty unusual for such hardware.  Normally there's something in
the digital block so that the discharge is only enabled if the regulator
is disabled, if it's enabled then the discharge would automatically be
taken off since actively discharging while enabled doesn't make sense
and may in fact be actively harmful.

If the hardware doesn't do that then I'd expect the driver to take care
of this if it implements the framework feature (once the framework
feature is added).

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