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

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Date:   Mon, 28 Nov 2022 09:41:03 -0800 (PST)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     heiko@...ech.de
CC:     linux-riscv@...ts.infradead.org,
        Conor Dooley <conor.dooley@...rochip.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Conor Dooley <conor@...nel.org>, 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 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?  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?

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

> 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
>>