Re: [PATCH v2 4/6] ACPI: ARM: exclude DMI calls

[Al Stone <al.stone@linaro.org>]

On 11/25/2013 10:45 AM, Matthew Garrett wrote:
> On Mon, Nov 25, 2013 at 10:43:27AM -0700, Al Stone wrote:
>> On 11/25/2013 08:30 AM, Matthew Garrett wrote:
>>> Is ACPI_REDUCED_HARDWARE supposed to indicate support for the reduced
>>> hardware profile, or that the platform *only* implements the reduced
>>> hardware profile?
>>
>>  From what I can see in ACPICA, ACPI_REDUCED_HARDWARE indicates the
>> platform *only* implements the reduced hardware profile.  This *seems*
>> to be consistent with the specification -- see 3.11.1, second bullet,
>> for example:
>
> Ok, so a kernel built without ACPI_REDUCED_HARDWARE would still support
> the reduced hardware profile?

Let me check on that.  The reduced hardware profile is a pretty
strict subset, and I think I can see a way where I could force
selecting the reduced HW profile on boot if the kernel has been
built *without* ACPI_REDUCED_HARDWARE.  What I am not convinced
of is that all of the proper guards are in place in ACPICA -- I
trust that they have been, but I would like to double check.

If I can get that to work properly, I'll add it to this patch set.

>> ...if by "not supported" one takes that to mean "does not exist when
>> compiled."  I can look at the ACPICA code again, just the same; perhaps
>> there is some reasonable way to at least select one or the other at boot
>> as the first step, and then allow switching between modes as a later
>> step.
>
> I don't think you'd ever want to switch after init time. There's a flag
> in the FADT that indicates whether a system is implementing the reduced
> hardware profile or not.
>

Agreed.  I could see it as something to use when experimenting perhaps,
but I think just allowing the switch at boot would cover the majority
of the use cases.

-- 
ciao,
al
-----------------------------------
Al Stone
Software Engineer
Linaro Enterprise Group
al.stone@linaro.org
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