Re: [PATCH V4 1/9] PM / OPP: Allow OPP table to be used for power-domains

From: Sudeep Holla <sudeep.holla@arm.com>
To: Mark Brown <broonie@kernel.org>, robh+dt@kernel.org
Cc: Sudeep Holla <sudeep.holla@arm.com>,
	Rajendra Nayak <rnayak@codeaurora.org>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Rafael Wysocki <rjw@rjwysocki.net>,
	ulf.hansson@linaro.org, Kevin Hilman <khilman@linaro.org>,
	Viresh Kumar <vireshk@kernel.org>, Nishanth Menon <nm@ti.com>,
	Stephen Boyd <sboyd@codeaurora.org>,
	linaro-kernel@lists.linaro.org, linux-pm@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Vincent Guittot <vincent.guittot@linaro.org>,
	lina.iyer@linaro.org, devicetree@vger.kernel.org
Subject: Re: [PATCH V4 1/9] PM / OPP: Allow OPP table to be used for power-domains
Date: Wed, 3 May 2017 12:21:54 +0100	[thread overview]
Message-ID: <8aacc296-2549-f0b8-ac25-2f4000c084c1@arm.com> (raw)
In-Reply-To: <20170430124917.4m3d237pik7q47f3@sirena.org.uk>

On 30/04/17 13:49, Mark Brown wrote:
> On Thu, Apr 27, 2017 at 10:42:49AM +0100, Sudeep Holla wrote:
>> On 26/04/17 14:55, Mark Brown wrote:
> 
>>> As I'm getting fed up of saying: if the values you are setting are not
>>> voltages and do not behave like voltages then the hardware should not be
>>> represented as a voltage regulator since if they are represented as
>>> voltage regulators things will expect to be able to control them as
>>> voltage regulators.  This hardware is quite clearly providing OPPs
>>> directly, I would expect this to be handled in the OPP code somehow.
> 
>> I agree with you that we need to be absolutely sure on what it actually
>> represents.
> 
>> But as more and more platform are pushing such power controls to
>> dedicated M3 or similar processors, we need abstraction. Though we are
>> controlling hardware, we do so indirectly. Since there were discussions
>> around device tree representing hardware vs platform, I tend to think,
>> we are moving towards platform(something similar to ACPI).
> 
> I don't think there's a meaningful hardware/platform distinction here -
> in terms of what DT is describing the platform bit is just what the
> hardware (the microcontrollers) happen to do, 
> 

Yes agreed. It's similar to PSCI or any other platform firmware IMO.

The question is how do we deal with such controls that needs to be done
via the firmware ? We generally plug-in to the existing framework in
Linux using the existing bindings. Most of the time, much simpler
bindings than the one that present complete hardware description.

> DT doesn't much care about that though.

No sure about that, may be doesn't care about the internals, but we need
to care about interface, no ?

-- 
Regards,
Sudeep