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

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Message-ID: <5596E0E5.9030300@redhat.com>
Date:	Fri, 03 Jul 2015 13:22:13 -0600
From:	Al Stone <ahs3@...hat.com>
To:	Hanjun Guo <guohanjun@...wei.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Al Stone <al.stone@...aro.org>
CC:	linux-acpi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	lenb@...nel.org, catalin.marinas@....com, will.deacon@....com,
	tglx@...utronix.de, jason@...edaemon.net,
	linux-kernel@...r.kernel.org, linaro-acpi@...ts.linaro.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org
Subject: Re: [PATCH v3 1/3] ACPI : introduce macros for using the ACPI specification
 version

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@...aro.org>
>>> ---
>>>  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.

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