linux-kernel - Re: ACPI vs Device Tree

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Message-ID: <20130820205712.GA22850@srcf.ucam.org>
Date:	Tue, 20 Aug 2013 21:57:13 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Darren Hart <dvhart@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux@...ck-us.net, hpa@...or.com, linus.walleij@...aro.org,
	rjw@...k.pl
Subject: Re: ACPI vs Device Tree - moving forward

On Tue, Aug 20, 2013 at 01:51:03PM -0700, Darren Hart wrote:

> It seems to me that the only way to end up in a situation where the data
> is reused by other OSes, is to go through a standards body. What about
> attempting to standardize the _DSM method? I suppose the challenge then
> is how do we standardize arbitrary data (which, of course, is an
> oxymoron)...

Right. We could certainly spec the DT bindings that currently exist, but 
the obvious pushback is that large chunks of it *are* already in ACPI - 
a _PS0 method (which is ACPI for "Power up the device") that toggles a 
GPIO pin, and then provides a different GPIO pin in the DT data, which 
would we believe?

> The interesting thing about this to me is that many of these devices are
> added after-the-fact (as add-on boards, for example). With the
> MinnowBoard we are looking to provide this configuration data in an
> EEPROM. Would it make sense for the device manufacturer (rather than the
> base-board manufacturer) to define the key-value pairs for their
> hardware?

Yes, hardware information that's on add-in boards should probably be 
provided by the add-in board if it carries a ROM. This is trivial on 
UEFI systems - you just need a UEFI driver for the board that can 
construct an appropriate SSDT. It's more of a problem for non-UEFI ACPI 
systems.

> Sadly, I will not be in New Orleans and am unlikely to receive a Kernel
> Summit invite, but I am planning be in Edinburgh and would like the
> opportunity to participate in this discussion.

I'm not planning on being at kernel summit this year, so I think we'll 
try to arrange something around that time but outside the event.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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