linux-kernel - Re: [PATCH] x86: Bypass legacy PIC and PIT on ACPI hardware reduced platform

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Message-ID: <8129220.9HmyqjfodP@vostro.rjw.lan>
Date:	Wed, 04 Mar 2015 22:52:38 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Alan Cox <alan@...ux.intel.com>
Cc:	Borislav Petkov <bp@...en8.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Li, Aubrey" <aubrey.li@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Len.Brown@...el.com,
	x86@...nel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: Bypass legacy PIC and PIT on ACPI hardware reduced platform

On Wednesday, March 04, 2015 08:21:01 PM Alan Cox wrote:
> On Wed, 2015-03-04 at 15:05 +0100, Borislav Petkov wrote:
> > On Wed, Mar 04, 2015 at 03:16:07PM +0100, Rafael J. Wysocki wrote:
> > > Sort of.  What we need is a "do not touch PIC/PIT" bit for the code that
> > > tries to fall back to them in some cases (which may appear to work if
> > > the hardware is physically there, but it may confuse the platform).
> > 
> > Can "some cases" detection be nicely put into a x86_platform
> > platform-specific method?
> 
> In some cases they don't belong in x86, ACPI is also used for ARM64.
> 
> However
> 
> 	if ( has_8259_pic() )
> 
> is trivally 0, 1 or some platform or acpi provided method.

And which is how that should have been implemented to start with IMO.

Besides, the "ACPI reduced hardware" case is kind of a red herring here,
because it most likely is not the only case when we'll want has_8259_pic()
to return 0 (quite likely, we'll want that on all BayTrail-based systems,
for example).


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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