linux-kernel - Re: [PATCH v4] regulator: qcom-saw: Add support for SAW regulators

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Date:	Wed, 10 Feb 2016 11:04:36 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Mark Brown <broonie@...nel.org>
Cc:	Georgi Djakov <georgi.djakov@...aro.org>,
	Lina Iyer <lina.iyer@...aro.org>, lgirdwood@...il.com,
	andy.gross@...aro.org, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v4] regulator: qcom-saw: Add support for SAW regulators

On 02/10, Mark Brown wrote:
> On Wed, Feb 10, 2016 at 10:36:51AM -0800, Stephen Boyd wrote:
> > On 02/10, Georgi Djakov wrote:
> 
> > In some designs we have to talk to the PMIC with SPMI
> > transactions to change the mode depending on the voltages. How do
> > we plan to handle that case where the regulator control is split
> > between two busses, SPMI and MMIO?
> 
> Mixed control interfaces are in general a diaster with Linux, I'd
> suggest remonstrating with your system designers about doing them but in
> this case since it's a syscon presumably you could hang the device off
> the SPMI bus in the cases where that's in use.

Agreed about the mixed control interfaces, it's a total nightmare
to deal with. Luckily this problem is going to go away in the
future, but we're stuck with what we have for this generation of
chips.

I don't follow the rest of your mail though. Are you suggesting
that in this case we put the regulator control into the PMIC
regulator driver (qcom_spmi-regulator.c) and then use a
syscon/regmap there to change the voltages inside the MMIO bus?
That may work but we're going to need to update the binding for
the SPMI regulator driver then.

I'm not really excited about the binding we have here either.
We're going to have two places in DT where we've created a
regulator for the same physical regulator. One will be a child of
the SAW node on the MMIO bus, and another will be a child of the
PMIC on the SPMI/SSBI bus. In the end, they're both the same
regulator, so any constraints on one node will need to be applied
to the other node as well.

A final note, 8064 is paired with a PMIC on the SSBI bus. We
don't have an SSBI regulator driver upstream, so we would need
some driver + binding for that regulator style if we want to do
this for 8064.

-- 
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