Re: [PATCH v1 1/3] RISC-V: clarify ISA string ordering rules in cpu.c
From: Conor Dooley
Date: Thu Dec 01 2022 - 03:49:36 EST
On Thu, Dec 01, 2022 at 09:27:43AM +0100, Andrew Jones wrote:
> On Wed, Nov 30, 2022 at 11:41:24PM +0000, Conor Dooley wrote:
> > From: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> >
> > While the current list of rules may have been accurate when created
> > it now lacks some clarity in the face of isa-manual updates. Instead of
> > trying to continuously align this rule-set with the one in the
> > specifications, change the role of this comment.
> >
> > This particular comment is important, as the array it "decorates"
> > defines the order in which the ISA string appears to userspace in
> > /proc/cpuinfo.
> >
> > Re-jig and strengthen the wording to provide contributors with a set
> > order in which to add entries & note why this particular struct needs
> > more attention than others.
> >
> > While in the area, add some whitespace and tweak some wording for
> > readability's sake.
> >
> > Suggested-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
> > Signed-off-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> > ---
> > arch/riscv/kernel/cpu.c | 49 ++++++++++++++++++++++++++++++-----------
> > 1 file changed, 36 insertions(+), 13 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> > index 852ecccd8920..68b2bd0cc3bc 100644
> > --- a/arch/riscv/kernel/cpu.c
> > +++ b/arch/riscv/kernel/cpu.c
> > @@ -120,22 +120,45 @@ device_initcall(riscv_cpuinfo_init);
> > .uprop = #UPROP, \
> > .isa_ext_id = EXTID, \
> > }
> > +
> > /*
> > - * Here are the ordering rules of extension naming defined by RISC-V
> > - * specification :
> > - * 1. All extensions should be separated from other multi-letter extensions
> > - * by an underscore.
> > - * 2. The first letter following the 'Z' conventionally indicates the most
> > + * The canonical order of ISA extension names in the ISA string is defined in
> > + * chapter 27 of the unprivileged specification.
> > + *
> > + * Ordinarily, for in-kernel data structures, this order is unimportant but
> > + * isa_ext_arr defines the order of the ISA string in /proc/cpuinfo.
> > + *
> > + * The specification uses vague wording, such as should, when it comes to
> > + * ordering so for our purposes the following rules apply:
> > + *
> > + * 1. All multi-letter extensions must be separated from other multi-letter
>
> 1. All multi-letter extensions must be separated from other extensions by an
> underscore.
>
> (Because we always lead multi-letter extensions with underscore, even the
> first one, which follows the single-letter extensions.)
Yah, I need to think as if I am using De Morgan's... The DT ABI requires
"should" and permits this. The uAPI is "must"/"will" and always has an
_. I'll propagate that change to the docs patch too.
> > + * extensions by an underscore.
> > + *
> > + * 2. Additional standard extensions (starting with 'Z') must be sorted after
> > + * single-letter extensions and before any higher-privileged extensions.
> > +
> > + * 3. The first letter following the 'Z' conventionally indicates the most
> > * closely related alphabetical extension category, IMAFDQLCBKJTPVH.
> > - * If multiple 'Z' extensions are named, they should be ordered first
> > - * by category, then alphabetically within a category.
> > - * 3. Standard supervisor-level extensions (starts with 'S') should be
> > - * listed after standard unprivileged extensions. If multiple
> > - * supervisor-level extensions are listed, they should be ordered
> > + * If multiple 'Z' extensions are named, they should be ordered first by
> > + * category, then alphabetically within a category.
> > + *
> > + * 3. Standard supervisor-level extensions (starting with 'S') must be listed
> > + * after standard unprivileged extensions. If multiple
> > + * supervisor-level extensions are listed, they must be ordered
> > * alphabetically.
> > - * 4. Non-standard extensions (starts with 'X') must be listed after all
> > - * standard extensions. They must be separated from other multi-letter
> > - * extensions by an underscore.
> > + *
> > + * 4. Standard machine-level extensions (starting with 'Zxm') must be listed
> > + * after any lower-privileged, standard extensions. If multiple
> > + * machine-level extensions are listed, they must be ordered
> > + * alphabetically.
> > + *
> > + * 5. Non-standard extensions (starts with 'X') must be listed after all
> > + * standard extensions.
> ^and alphabetically.
"If multiple non-standard extensions are listed, they must be ordered
alphabetically." I'll also propagate this to the doc one, if I have not
already.
> Otherwise,
>
> Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
Cool. I'll give it a bit before respinning, but I think we are at least
getting less ambiguous as time goes on..
Thanks,
Conor.