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

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Date:	Thu, 05 Mar 2015 19:26:19 +0800
From:	"Li, Aubrey" <aubrey.li@...ux.intel.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	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>,
	"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 2015/3/5 5:52, Rafael J. Wysocki wrote:
> 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).
> 
BayTrail-based systems has BayTrail-I, BayTrail-M, BayTrail-D,
BayTrail-T, BayTrail-T/CR. BayTrail-D is a desktop and BayTrail-M is a
mobile/laptop and 8259 exists on both systems and I don't think we want
to bypass it.

ACPI reduced hardware is the best case in my mind unless you want to
enumerate the platform one by one. can we make a global variable

u8 has_8259;

and initialize it by acpi reduced hardware flag? or a wrapper function?

Thanks,
-Aubrey
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