On Fri, Jul 15, 2022 at 11:26:36AM +1000, Nicholas Piggin wrote:

Take the arm64 HWCAP documentation file and adjust it for powerpc.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Reviewed-by: Segher Boessenkool <redacted>

+2. Facilities
+-------------
+
+The Power ISA uses the term "facility" to describe a class of instructions,
+registers, interrupts, etc. The presence or absence of a facility indicates
+whether this class is available to be used, but the specifics depend on the
+ISA version. For example, if the VSX facility is available, the VSX
+instructions that can be used differ between the v3.0B and v3.1B ISA
+versions.

The term "facility" is never defined in the architecture documents, so
the common language meaning applies, which google says is "a place,
amenity, or piece of equipment provided for a particular purpose", which
fits your explanation well.

+3. Categories
+-------------
+
+The Power ISA before v3.0 uses the term "category" to describe certain
+classes of instructions and operating modes which may be optional or
+mutually exclusive, the exact meaning of the HWCAP flag may depend on
+context, e.g., the presence of the BOOKE feature implies that the server
+category is not implemented.

Since ISA 3.0 the preface says
  The resulting architecture included [...] and optional application-
  specific facilities (categories) as extensions to a pervasive base
  architecture.
which fits your explanation.

Thanks for improving the documentation!


Segher