linux-kernel - Re: [PATCH 0/7] Implement generic regulator constraints parsing for ACPI and OF

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Date:   Wed, 25 Jan 2017 16:33:42 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Al Stone <ahs3@...hat.com>
Cc:     Mark Brown <broonie@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Furquan Shaikh <furquan@...omium.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Liam Girdwood <lgirdwood@...il.com>,
        Tony Lindgren <tony@...mide.com>, Len Brown <lenb@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Rob Herring <robh@...nel.org>,
        Sathyanarayana Nujella <sathyanarayana.nujella@...el.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Adam Thomson <Adam.Thomson.Opensource@...semi.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Alexandre Courbot <gnurou@...il.com>,
        linux-gpio@...r.kernel.org,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
        Aaron Durbin <adurbin@...omium.org>, dlaurie@...omium.org
Subject: Re: [PATCH 0/7] Implement generic regulator constraints parsing for
 ACPI and OF

On Wed, Jan 25, 2017 at 05:15:52PM -0700, Al Stone wrote:
> On 01/25/2017 04:27 PM, Dmitry Torokhov wrote:
> > On Wed, Jan 25, 2017 at 02:44:10PM -0700, Al Stone wrote:
> >>
> >> But, to the point of some of the other discussion on the thread, this ACPI sort
> >> of power management is a very, very different model than DT so that intertwining
> >> the two models is highly unlikely to work, IMHO.
> > 
> > And yet this is something that is sorely needed. If you look, for
> > example, at drivers in drivers/input/*, then all non-SOC-specific
> > devices can easily find their way onto both ACPI-based and DT-based
> > systems (not mentioning legacy-style boards). Having two distinct power
> > schemes implemented in drivers will lead to many problems.
> 
> I really can't speak to those sorts of systems; where I deal with ACPI
> is on enterprise-class server systems which seldom have a graphics card,
> much less input devices other than a keyboard. 

Yeah, so basically no power management except for CPU states ;)

> And in general, those
> systems are required to use only ACPI.  If a vendor wants their device to
> work on such a system, they need to provide a driver that works with ACPI.
> It may also work with DT, but in this environment it doesn't matter.
> 
> Whether or not there are two power schemes is a moot point.  We have DT
> and we have ACPI, and they have very different schemes for power management,
> so we're already there.  And so far, my experience has been that as long as
> the ACPI and DT parts of the driver are kept disjoint when the models diverge,
> and share code when they are semantically absolutely identical, things work
> pretty well.

As someone who's actually shipping both ACPI and DT-based devices
reusing the same peripherals I can assure you that it is really PITA to
have different PM behavior in a single driver and if we can converge on
something sane that would be great.

> 
> > Having unified way of describing hardware is how _DSD came about, right?
> > Nobody wanted to write and maintain and test two separate ways of
> > describing properties when one was already implemented and working.
> 
> I can't speak for those that proposed _DSD to be part of the ACPI spec,
> but no, it was not meant as a unified way of describing hardware, as far
> as I can remember from the ASWG discussions I was part of.  The intent,
> as I recall it, was to provide some of the same flexibility to ASL that
> was available in DT.  At the time, power managment was even discussed as
> one of the areas where the DT model and the ACPI model clashed.

That's not what I remember from discussions at Plumbers/KS... Binding
compatibility, even if for simplest properties, was one of the points.

Thanks.

-- 
Dmitry