linux-kernel - Re: [PATCH v3 01/15] ACPI: Add support for device specific properties

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Date:	Wed, 01 Oct 2014 09:38:12 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	linux-kernel@...r.kernel.org,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	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 01/15] ACPI: Add support for device specific properties

On Wednesday 01 October 2014 04:08:56 Rafael J. Wysocki wrote:
> From: Mika Westerberg <mika.westerberg@...ux.intel.com>
> 
> Device Tree is used in many embedded systems to describe the system
> configuration to the OS. It supports attaching properties or name-value
> pairs to the devices it describe. With these properties one can pass
> additional information to the drivers that would not be available
> otherwise.
> 
> ACPI is another configuration mechanism (among other things) typically
> seen, but not limited to, x86 machines. ACPI allows passing arbitrary
> data from methods but there has not been mechanism equivalent to Device
> Tree until the introduction of _DSD in the recent publication of the
> ACPI 5.1 specification.
> 
> In order to facilitate ACPI usage in systems where Device Tree is
> typically used, it would be beneficial to standardize a way to retrieve
> Device Tree style properties from ACPI devices, which is what we do in
> this patch.
> 
> If a given device described in ACPI namespace wants to export properties it
> must implement _DSD method (Device Specific Data, introduced with ACPI 5.1)
> that returns the properties in a package of packages. For example:
> 
>         Name (_DSD, Package () {
>                 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
>                 Package () {
>                         Package () {"name1", <VALUE1>},
>                         Package () {"name2", <VALUE2>},
>                         ...
>                 }
>         })
> 
> The UUID reserved for properties is daffd814-6eba-4d8c-8a91-bc9bbf4aa301
> and is documented in the ACPI 5.1 companion document called "_DSD
> Implementation Guide" [1], [2].
> 
> We add several helper functions that can be used to extract these
> properties and convert them to different Linux data types.
> 
> The ultimate goal is that we only have one device property API that
> retrieves the requested properties from Device Tree or from ACPI
> transparent to the caller.
> 
> [1] http://www.uefi.org/sites/default/files/resources/_DSD-implementation-guide-toplevel.htm
> [2] http://www.uefi.org/sites/default/files/resources/_DSD-device-properties-UUID.pdf
> 
> Reviewed-by: Hanjun Guo <hanjun.guo@...aro.org>
> Reviewed-by: Josh Triplett <josh@...htriplett.org>
> Signed-off-by: Darren Hart <dvhart@...ux.intel.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 

Looks good to me.

Acked-by: Arnd Bergmann <arnd@...db.de>
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