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SubjectRe: [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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