Subject: [RFC] ACPI on arm64 TODO List

From: [email-masked] (Al Stone)
Date: Tue, 16 Dec 2014 17:03:06 -0700

On 12/16/2014 08:27 AM, Catalin Marinas wrote:
> On Tue, Dec 16, 2014 at 11:27:48AM +0000, Arnd Bergmann wrote:
>> On Monday 15 December 2014 19:18:16 Al Stone wrote:
>>> TODO List for ACPI on arm64:
>>> ============================
[snip..]
>>> 4. Set clear expectations for those providing ACPI for use with Linux
>>>    * Problem:
>>>      * Hardware/Firmware vendors can and will create ACPI tables that
>>>        cannot be used by Linux without some guidance
>>>      * Kernel developers cannot determine whether the kernel or firmware
>>>        is broken without knowing what the firmware should do
>>>    * Solution: document the expectations, and iterate as needed.
>>>      Enforce when we must.
>>>    * Status: initial kernel text available; AMD has offered to make
>>>      their guidance document generic; firmware summit planned for
>>>      deeper discussions.
>>
[snip...]
> 
> Another example is SMP booting. The ACPI 5.1 spec mentions the parking
> protocol but I can't find a reference to the latest document. In the
> meantime, we stick to PSCI.

Hrm.  A bug in the spec.

Every external document mentioned in the ACPI spec is supposed to have
a link that will eventually get you to the source document.  All links
in the spec should point here http://www.uefi.org/acpi which in turn
has links to the authoritative original documents.  However, it looks
like the parking protocol document pointed to (the "Multiprocessor
Startup" link) may not be the most recent version.  The reference in
the spec to the protocol (Table 5-61, Section 5.2.12.14)) also appears
to be useless (it points to http://infocenter.arm.com/help/index.jsp
which doesn't have the document either).  I've filed a change request
with ASWG to fix this.

That being said, the early systems still don't provide PSCI.  They will
at some point in the future, but not now.  Regardless, I think it's
reasonable for us to say that if you want ACPI support, PSCI must be
used for secondary CPU startup.  People can hack something up to get
the parking protocol to work on development branches if they want, but
I personally see no need to get that into the kernel -- and it needs
to be said explicitly in arm-acpi.txt.

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