linux-kernel - Re: [PATCH v3 04/15] ACPI: Document ACPI device specific properties

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Message-ID: <20141002121508.GM1786@lahna.fi.intel.com>
Date:	Thu, 2 Oct 2014 15:15:08 +0300
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	devicetree@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Bryan Wu <cooloney@...il.com>,
	Lee Jones <lee.jones@...aro.org>,
	Grant Likely <grant.likely@...aro.org>,
	Aaron Lu <aaron.lu@...el.com>,
	Darren Hart <dvhart@...ux.intel.com>
Subject: Re: [PATCH v3 04/15] ACPI: Document ACPI device specific properties

On Thu, Oct 02, 2014 at 01:51:24PM +0200, Arnd Bergmann wrote:
> On Thursday 02 October 2014 13:41:23 Mika Westerberg wrote:
> > On Wed, Oct 01, 2014 at 09:59:14AM +0200, Arnd Bergmann wrote:
> > > On Wednesday 01 October 2014 04:11:20 Rafael J. Wysocki wrote:
> > > > From: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > 
> > > > +The referenced ACPI device is returned in args->adev if found.
> > > > +
> > > > +In addition to simple object references it is also possible to have object
> > > > +references with arguments. These are represented in ASL as follows:
> > > > +
> > > > +	Device (\_SB.PCI0.PWM)
> > > > +	{
> > > > +		Name (_DSD, Package () {
> > > > +			ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> > > > +			Package () {
> > > > +				Package () {"#pwm-cells", 2}
> > > > +			}
> > > > +		})
> > > > +	}
> > > > +
> > > 
> > > Similarly, the "#foo-cells" syntax is an artifact of the limitations of the
> > > DT syntax, and I'd assume there would be a better way to encode this
> > > in ACPI. Also, a "cell" in Open Firmware is defined as a big-endian
> > > 32-bit value, which doesn't directly correspond to something in ACPI,
> > > and the '#' character is an artifact of the use of the Forth language
> > > in Open Firmware, which you also don't have here.
> > 
> > Same here, we tried to make it follow closely the DT description. It is
> > probably not the best/optimal encoding for ACPI but it is documented
> > well in Documentation/devicetree/bindings so why not use it.
> > 
> > The summary email from Darren at KS also mentions that for the existing
> > drivers, the existing schemas should be common for both implementations [1].
> > 
> > For new bindings we probably should look out if they can be better
> > represented using ACPI types.
> > 
> > [1] http://lwn.net/Articles/609373/
> 
> I thought when we had discussed the subsystem specific bindings, the
> consensus there was to have subsystem specific accessors and
> properties/tables.
> 
> I would argue that for everything that ACPI already has (interrupts,
> registers, gpio, dmaengine, ...) the native method should be used,
> possibly using _DSD to provide naming for otherwise anonymous references.

Absolutely. That's precisely what we do in the GPIO patch of this
series. E.g we use ACPI GpioIo/GpioInt _CRS resources but give name to
the GPIOs with the help of _DSD.

For things that don't have correspondence in ACPI but have well defined
existing DT schema, like PWMs, we should follow that.
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