Re: [PATCH v4] ARM64: ACPI: Update documentation for latest specification version

[Al Stone]

On 04/21/2016 07:37 AM, Alexey Klimov wrote:
> Hi Al,
> 
> I hope you don't mind if I put few minor questions here.
> 
> On Mon, Apr 18, 2016 at 8:32 PM, Al Stone <al.stone@xxxxxxxxxx> wrote:
>> The ACPI 6.1 specification was recently released at the end of January
>> 2016, but the arm64 kernel documentation for the use of ACPI was written
>> for the 5.1 version of the spec.  There were significant additions to the
>> spec that had not yet been mentioned -- for example, the 6.0 mechanisms
>> added to make it easier to define processors and low power idle states,
>> as well as the 6.1 addition allowing regular interrupts (not just from
>> GPIO) be used to signal ACPI general purpose events.
>>
>> This patch reflects going back through and examining the specs in detail
>> and updating content appropriately.  Whilst there, a few odds and ends of
>> typos were caught as well.  This brings the documentation up to date with
>> ACPI 6.1 for arm64.
> 
> Why linux-acpi is not in the destination list?

No particular reason; I can add it to the next version, but this was meant
to be arm64-specific documentation that just happens to be a user of ACPI.
There are no changes to ACPI itself implied or intended.

>> Changes for v4:
>>    -- Clarify that IORT can sometimes be optional (Jon Masters).
>>    -- Remove "Use as needed" descriptions of ACPI objects; they provide
>>       no substantive information and doing so simplifies maintenance of
>>       this document over time.  These have been replaced with a simpler
>>       notice that states that unless otherwise noted, do what the APCI
>>       specification says is needed.
>>    -- Corrected the _OSI object usage recommendation; it described kernel
>>       behavior that does not exist (Al Stone).
>>
>> Changes for v3:
>>    -- Clarify use of _LPI/_RDI (Vikas Sajjan)
>>    -- Whitespace cleanup as pointed out by checkpatch
>>
>> Changes for v2:
>>    -- Clean up white space (Harb Abdulhahmid)
>>    -- Clarification on _CCA usage (Harb Abdulhamid)
>>    -- IORT moved to required from recommended (Hanjun Guo)
>>    -- Clarify IORT description (Hanjun Guo)
>>
>> Signed-off-by: Al Stone <al.stone@xxxxxxxxxx>
>> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
>> Cc: Will Deacon <will.deacon@xxxxxxx>
>> Cc: Jonathan Corbet <corbet@xxxxxxx>
>> ---
>>  Documentation/arm64/acpi_object_usage.txt | 347 ++++++++++++++++--------------
>>  Documentation/arm64/arm-acpi.txt          |  28 ++-
>>  2 files changed, 212 insertions(+), 163 deletions(-)
>>
>> diff --git a/Documentation/arm64/acpi_object_usage.txt
>> b/Documentation/arm64/acpi_object_usage.txt
>> index a6e1a18..3891750 100644
>> --- a/Documentation/arm64/acpi_object_usage.txt
>> +++ b/Documentation/arm64/acpi_object_usage.txt
>> @@ -13,14 +13,18 @@ For ACPI on arm64, tables also fall into the
>> following categories:
> 
> [..]
> 
>>         == Memory-mapped ConFiGuration space ==
>> @@ -176,14 +192,38 @@ MPST   Section 5.2.21 (signature == "MPST")
>>         == Memory Power State Table ==
>>         Optional, not currently supported.
>>
>> +MSCT   Section 5.2.19 (signature == "MSCT")
>> +       == Maximum System Characteristic Table ==
>> +       Optional, not currently supported.
>> +
>>  MSDM   Signature Reserved (signature == "MSDM")
>>         == Microsoft Data Management table ==
>>         Microsoft only table, will not be supported.
>>
>> -MSCT   Section 5.2.19 (signature == "MSCT")
>> -       == Maximum System Characteristic Table ==
>> +NFIT   Section 5.2.25 (signature == "NFIT")
>> +       == NVDIMM Firmware Interface Table ==
>>         Optional, not currently supported.
>>
>> +OEMx   Signature of "OEMx" only
>> +       == OEM Specific Tables ==
>> +       All tables starting with a signature of "OEM" are reserved for OEM
>> +       use.  Since these are not meant to be of general use but are limited
>> +       to very specific end users, they are not recommended for use and are
>> +       not supported by the kernel for arm64.
>> +
>> +PCCT   Section 14.1 (signature == "PCCT)
>> +       == Platform Communications Channel Table ==
>> +       Recommend for use on arm64, and required when using CPPC to control
>> +       power on the platform.
> 
> Could you please check corectness of this sentence?
> 
> If I remember correctly CPPC may operate via PCC interface but there is no
> strict requirement to implement control mechanism via PCC.

On double checking, no, it is not a strict requirement to use PCC.  So this
should probably be something like:

	Recommended for use on arm64; use of PCC is recommended when using
	CPPC.

>> using CPPC to control power on the platform
> 
> Sorry, I think I need to disagree.
> Main description of CPPC says that CPPC defines mechanism to manage performance
> of logical processor.

Ah.  Yup, CPPC is just for processors.  Thanks for catching that.

> What do you think about "to control performance on the platform"?
> (or maybe "to control performance and power on the platform")
> 
> Thanks,
> Alexey
> 

Perhaps just "using CPPC to control performance and power for platform
processors" -- there are of course all the other portions of ACPI to
control device power, but not related to CPPC.

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