linux-kernel - Re: [PATCH v2 1/3] ACPI : introduce macros for using the ACPI specification version

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Message-ID: <559306E2.7000901@linaro.org>
Date:	Tue, 30 Jun 2015 15:15:14 -0600
From:	Al Stone <al.stone@...aro.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
CC:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	"patches@...aro.org" <patches@...aro.org>
Subject: Re: [PATCH v2 1/3] ACPI : introduce macros for using the ACPI specification
 version

On 06/30/2015 02:12 PM, Rafael J. Wysocki wrote:
> Hi Al,
> 
> On Fri, Jun 19, 2015 at 12:36 AM, Al Stone <al.stone@...aro.org> wrote:
>> Add the ACPI_SPEC_VERSION() macro to build a proper version number from
>> a major and minor revision number.  Add also the ACPI_FADT_SPEC_VERSION
>> that constructs a proper version number from the entries in the current
>> FADT.
>>
>> 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.
>>
>> Signed-off-by: Al Stone <al.stone@...aro.org>
>> ---
>>  include/linux/acpi.h | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
>> index a4acb55..33ed313 100644
>> --- a/include/linux/acpi.h
>> +++ b/include/linux/acpi.h
>> @@ -48,6 +48,11 @@
>>  #include <acpi/acpi_io.h>
>>  #include <asm/acpi.h>
>>
>> +#define ACPI_SPEC_VERSION(major, minor)        ((major<<8)|minor)
> 
> One nit here.
> 
> acpi_gbl_FADT.header.revision is of type u8 originally, so shifting it
> by 8 bit positions only works due to some implicit type casting I
> suppose.

Bah.  That was being sloppy on my part.  Sorry about that.  Will fix.

> Moreover, it is not entirely clear why the macro is specific to the
> computation of the ACPI spec version.

As far as I know, that's the only way to extract the spec version from
tables; I don't recall there being any other table with that info.  Since
I will likely use this again, it seemed to make sense at the time.

> So I'd drop ACPI_SPEC_VERSION and only define ACPI_FADT_SPEC_VERSION
> as something like
> 
> #define ACPI_FADT_SPEC_VERSION (((unsigned
> int)acpi_gbl_FADT.header.revision << 8) | (unsigned
> int)acpi_gbl_FADT.minor_revision)
> 
> Thanks,
> Rafael
> 

Sure.  That makes sense.  It makes it clearer that this is the version
just from the FADT.  I'll do that.

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