linux-kernel - Re: [PATCH v4 00/13] Add ACPI _DSD and unified device properties support

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Message-ID: <db4038336b5e165b8b61eda064b10eeb.squirrel@twosheds.infradead.org>
Date:	Wed, 15 Oct 2014 14:08:09 -0000
From:	"David Woodhouse" <dwmw2@...radead.org>
To:	"Mark Rutland" <mark.rutland@....com>
Cc:	"David Woodhouse" <dwmw2@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	"Mika Westerberg" <mika.westerberg@...ux.intel.com>,
	"ACPI Devel Maling List" <linux-acpi@...r.kernel.org>,
	"Aaron Lu" <aaron.lu@...el.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"Linus Walleij" <linus.walleij@...aro.org>,
	"Alexandre Courbot" <gnurou@...il.com>,
	"Dmitry Torokhov" <dmitry.torokhov@...il.com>,
	"Bryan Wu" <cooloney@...il.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"Arnd Bergmann" <arnd@...db.de>,
	"Darren Hart" <dvhart@...ux.intel.com>
Subject: Re: [PATCH v4 00/13] Add ACPI _DSD and unified device properties
 support


> We have been checking for all DT platforms, and that's a bug for DT.
> Copying that bug to ACPI is inexcusable given we know it's a bug to do
> so.

We'll, perhaps it should be named 'used-by-firmware' and actually it's
just as valid under ACPI as it is on RTAS systems. All it does is stop the
OS from using the port.

> I understand that. However, where a binding doesn't make sense (as in
> this case), it shouldn't be enabled for ACPI as it provides a larger
> surface area for misuse, for no benefit.

These are *optional* properties. They were optional precisely *because*
they only make sense in some cases. I don't know that it makes sense to
take them away. The benefit we get is *consistency*. For example if
someone *does* use the property in question as 'used-by-firmware' and
expects the OS not to touch it, we don't want that to change behaviour
between ACPI and fdt boots.

-- 
dwmw2

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