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 <redacted>
---
 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)