Re: [PATCH v3 1/3] ACPI : introduce macros for using the ACPI specification version

[Al Stone]

On 07/03/2015 05:50 PM, Rafael J. Wysocki wrote:
> On Friday, July 03, 2015 01:22:13 PM Al Stone wrote:
>> On 07/02/2015 11:23 PM, Hanjun Guo wrote:
>>> Hi Rafael,
>>>
>>> On 2015/7/3 8:21, Rafael J. Wysocki wrote:
>>>> On Thursday, July 02, 2015 05:48:34 PM Al Stone wrote:
>>>>> Add the __ACPI_FADT_SPEC_VERSION() helper macro to build a proper version
>>>>> number from a major and minor revision number.  Add also macros that use
>>>>> the helper to construct the current version from the values in the FADT
>>>>> (i.e., ACPI_FADT_SPEC_VERSION) and both the 5.1 and 6.0 versions.
>>>>>
>>>>> These macros are added in order to simplify retrieving and comparing ACPI
>>>>> specification version numbers, since this is becoming a more frequent need.
>>>>> In particular, there are some architectures that require at least a certain
>>>>> version of the spec, and there are differences in some structure sizes that
>>>>> have changed with recent versions but can only be tracked by spec version
>>>>> number.
>>>>>
>>>>> Fixes: aeb823bbacc2 (ACPICA: ACPI 6.0: Add changes for FADT table.)
>>>>> Signed-off-by: Al Stone <al.stone@xxxxxxxxxx>
>>>>> ---
>>>>>  include/linux/acpi.h | 10 ++++++++++
>>>>>  1 file changed, 10 insertions(+)
>>>>>
>>>>> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
>>>>> index c471dfc..0e525e8 100644
>>>>> --- a/include/linux/acpi.h
>>>>> +++ b/include/linux/acpi.h
>>>>> @@ -48,6 +48,16 @@
>>>>>  #include <acpi/acpi_io.h>
>>>>>  #include <asm/acpi.h>
>>>>>  
>>>>> +#define __ACPI_FADT_SPEC_VERSION(major, minor) \
>>>>> +	((unsigned int)major << 8 | (unsigned int)minor)
>>>>> +
>>>>> +#define ACPI_FADT_SPEC_VERSION	\
>>>>> +	__ACPI_FADT_SPEC_VERSION(acpi_gbl_FADT.header.revision, \
>>>>> +				 acpi_gbl_FADT.minor_revision)
>>>>> +
>>>>> +#define ACPI_FADT_SPEC_VERSION_51 __ACPI_FADT_SPEC_VERSION(5, 1)
>>>>> +#define ACPI_FADT_SPEC_VERSION_60 __ACPI_FADT_SPEC_VERSION(6, 0)
>>>> I'd add underscores here, eg. ACPI_FADT_SPEC_VERSION_6_0
>>>
>>> Agreed.
>>
>> Will do.  This was a flip of the coin, on my part.
>>
>>>> And what if there is 5.2 or even 5.3?
>>>
>>> Hmm, do you mean in the future or just now? for both two cases,
>>> only 5.1 and 5.1 errata (still has the same ACPI version with 5.1)
>>> will be available, then jump to 6.0 and going forward if new versions
>>> in the future.
>>>
>>> I'm not sure if I understand your question correctly, if
>>> not, please correct me :)
>>>
>>> Thanks
>>> Hanjun
>>
>> I'm not sure I understand the question, either.  Traditionally, the
>> spec versioning has been exclusively linear -- i.e., now that 6.0
>> has replaced 5.1, there will be no more 5.x.  There may be errata
>> published (e.g., there was a 5.1A, and a 6.0A is forthcoming) but
>> the errata are not encoded in tables anywhere since they are meant
>> only as corrections to the base version.  This is unlikely to change,
>> but not impossible, of course :).
>>
>> The only reason for putting in macros for 5.1 and 6.0 is that those
>> are the versions that I'm concerned with for this particular fix and
>> I know I will use them.  If others are needed, I'd have those that
>> need them add them.
> 
> It seems to me that you only need to compare acpi_gbl_FADT.header.revision
> with 6 for this fix, though (if less than 6, use the old way, or use the
> new way otherwise).
> 
> Isn't that the case?
> 
> Rafael
> 

Ah, sorry for being a bit dense.  Yes, on arm64 we only support 5.1 or
later so for now, less than 6 is a sufficient test.  The 5.0 spec defines
yet a third size for the GICC subtable with the same MADT version number
(40 bytes) but we won't initialize ACPI if we have anything before 5.1.

So, I could take this patch out of the set and reduce patch 2/3 somewhat
by just comparing against acpi_gbl_FADT.header.revision.  I think that's
what I'll do unless you think these macros have intrinsic value for other
reasons.

-- 
ciao,
al
-----------------------------------
Al Stone
Software Engineer
Red Hat, Inc.
ahs3@xxxxxxxxxx
-----------------------------------
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