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

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Message-ID: <1425500337.3838.138.camel@linux.intel.com>
Date:	Wed, 04 Mar 2015 20:18:57 +0000
From:	Alan Cox <alan@...ux.intel.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	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>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, 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 Wed, 2015-03-04 at 10:50 +0100, Borislav Petkov wrote:
> On Wed, Mar 04, 2015 at 12:43:08AM -0800, Arjan van de Ven wrote:
> > >
> > >Using 'acpi_gbl_reduced_hardware' flag outside the ACPI code
> > >is a mistake.
> > 
> > ideally, the presence of that flag in the firmware table will clear/set more global settings,
> > for example, having that flag should cause the 8042 input code to not probe for the 8042.
> > 
> > for interrupts, there really ought to be a "apic first/only" mode, which is then used on
> > all modern systems (not just hw reduced).
> 
> Do we need some sort of platform-specific querying interfaces now too,
> similar to cpu_has()? I.e., platform_has()...
> 
> 	if (platform_has(X86_PLATFORM_REDUCED_HW))
> 		do stuff..

ACPI hw reduced is not an x86 specific concept so quite possibly yes.

ACPI is the usual source for a variety of generic platform information
such as absence and presence of prehistoric PC compatibility goo -
increasingly so in fact. It tells you if the device is probably a
tablet, if it is more efficient to idle via suspend/resume or by asking
the cpu to idle. It tells you if low power modes are supported and so
on.

I don't think it makes sense to treat "ACPI reduced" as some kind of
platform concept. You could easily get basically identical hardware that
is or is not "hw reduced" depending upon firmware choices.

Alan


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