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

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Date:	Tue, 30 Jun 2015 22:12:34 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Al Stone <al.stone@...aro.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

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.

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

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
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