linux-kernel - Re: [PATCH 2/2] dt-bindings: riscv: fix single letter canonical order

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Date:   Mon, 28 Nov 2022 18:08:05 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     heiko@...ech.de, linux-riscv@...ts.infradead.org,
        Conor Dooley <conor.dooley@...rochip.com>, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        aou@...s.berkeley.edu, ajones@...tanamicro.com, guoren@...nel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] dt-bindings: riscv: fix single letter canonical order

On Mon, Nov 28, 2022 at 09:41:03AM -0800, Palmer Dabbelt wrote:
> On Thu, 24 Nov 2022 05:42:20 PST (-0800), heiko@...ech.de wrote:
> > Am Donnerstag, 24. November 2022, 14:04:41 CET schrieb Conor Dooley:
> > > I used the wikipedia table for ordering extensions when updating the
> > > pattern here in foo.
> > 
> > 	    ^ foo? :-)
> > 
> > > Unfortunately that table did not match canonical order, as defined by
> > > the RISC-V ISA Manual, which defines extension ordering in (what is
> > > currently) Table 41, "Standard ISA extension names". Fix things up by
> > > re-sorting v (vector) and adding p (packed-simd) & j (dynamic
> > > languages). The e (reduced integer) and g (general) extensions are still
> > > intentionally left out.
> > > 
> > > Link: https://github.com/riscv/riscv-isa-manual/releases/tag/riscv-unpriv-pdf-from-asciidoc-15112022 # Chapter 29.5
> > > Fixes: 299824e68bd0 ("dt-bindings: riscv: add new riscv,isa strings for emulators")
> > > Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>
> > 
> > So I have compared the new pattern to the isa manual,
> > and it looks like the order checks out, so
> 
> Which ISA manual?

For me, isa manual is the above github repo.

> There have been many mutually incompatible ISA string
> encoding rules, at least one of them was a change to the extension ordering.
> It's not entirely clear what the right answer is here, as we can't really
> parse ISA strings without also knowing the version of the ISA manual we're
> meant to parse them against.  Maybe we just accept everything?

I don't think accepting everything is the right thing to do. A minimal
amount of validation is still needed here, but I think we can deprecate
the DT property entirely & make it optional if a new-and-improved way of
encoding the in DT is used.

> IMO it's time to just stop using the ISA string.  It's not a stable
> interface, trying to treat it as such just leads to headaches.  We should
> just come up with some DT-specific way of encoding whatever HW features are
> in question.  Sure it'll be a bit of work to write that all down in the DT
> bindings, but it's going to be way less work than trying to keep around all
> this ISA string parsing code.

I'm a glutton for punishment, I'll try and come up with some sort of
other way to encode this information in DT that requires less parsing
and validation. As I said on IRC, something that more resembles:
if (of_property_wahtever("riscv,isa-foo")) { do_enable_foo() }

> I know I've said the opposite before, but there's just been way too many
> breakages here to assume they're going to stop.

:upside_down_face:

Either way, I think these two patches are worth taking in the mean time.

> > Reviewed-by: Heiko Stuebner <heiko@...ech.de>
> > 
> > > ---
> > >  Documentation/devicetree/bindings/riscv/cpus.yaml | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > > index e80c967a4fa4..b7462ea2dbe4 100644
> > > --- a/Documentation/devicetree/bindings/riscv/cpus.yaml
> > > +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > > @@ -80,7 +80,7 @@ properties:
> > >        insensitive, letters in the riscv,isa string must be all
> > >        lowercase to simplify parsing.
> > >      $ref: "/schemas/types.yaml#/definitions/string"
> > > -    pattern: ^rv(?:64|32)imaf?d?q?c?b?v?k?h?(?:z(?:[a-z])+)?(?:_[hsxz](?:[a-z])+)*$
> > > +    pattern: ^rv(?:64|32)imaf?d?q?c?b?k?j?p?v?h?(?:z(?:[a-z])+)?(?:_[hsxz](?:[a-z])+)*$
> > > 
> > >    # RISC-V requires 'timebase-frequency' in /cpus, so disallow it here
> > >    timebase-frequency: false
> > >