linux-kernel - Re: [PATCH v3 3/4] dt-bindings: riscv: add new riscv,isa strings for emulators

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Date:   Thu, 18 Aug 2022 07:48:53 +0200
From:   Andrew Jones <ajones@...tanamicro.com>
To:     Conor Dooley <mail@...chuod.ie>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Anup Patel <anup@...infault.org>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Guo Ren <guoren@...nel.org>,
        Sagar Kadam <sagar.kadam@...ive.com>,
        Jessica Clarke <jrtc27@...c27.com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-riscv@...ts.infradead.org, qemu-riscv@...gnu.org,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v3 3/4] dt-bindings: riscv: add new riscv,isa strings for
 emulators

On Thu, Aug 18, 2022 at 07:40:14AM +0200, Andrew Jones wrote:
> On Wed, Aug 17, 2022 at 09:12:12PM +0100, Conor Dooley wrote:
> > From: Conor Dooley <conor.dooley@...rochip.com>
> > 
> > The QEMU virt and spike machines currently export a riscv,isa string of
> > "rv64imafdcsuh",
> > 
> > While the RISC-V foundation has been ratifying a bunch of extenstions
> > etc, the kernel has remained relatively static with what hardware is
> > supported - but the same is not true of QEMU. Using the virt machine
> > and running dt-validate on the dumped dtb fails, partly due to the
> > unexpected isa string.
> > 
> > Rather than enumerate the many many possbilities, change the pattern
> > to a regex, with the following assumptions:
> > - the single letter order is fixed & we don't care about things that
> >   can't even do "ima"
> > - the standard multi letter extensions are all in a "_z<foo>" format
> >   where the first letter of <foo> is a valid single letter extension
> > - _s & _h are used for supervisor and hyper visor extensions.
> > - after the first two chars, a standard multi letter extension name
> >   could be an english   word (ifencei anyone?) so it's not worth
> >   restricting the charset
> > - vendor ISA extensions begind with _x and have no charset restrictions
> > - we don't care about an e extension from an OS pov
> > - that attempting to validate the contents of the multiletter extensions
> >   with dt-validate beyond the formatting is a futile, massively verbose
> >   or unwieldy exercise at best.
> > - ima are required
> > 
> > The following limitations also apply:
> > - multi letter extension ordering is not enforced. dt-schema does not
> >   appear to allow for named match groups, so the resulting regex would
> >   be even more of a headache.
> > - ditto for the numbered extensions.
> > 
> > Finally, add me as a maintainer of the binding so that when it breaks
> > in the future, I can be held responsible!
> > 
> > Reported-by: Rob Herring <robh@...nel.org>
> > Link: https://lore.kernel.org/linux-riscv/20220803170552.GA2250266-robh@kernel.org/
> > Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>
> > ---
> > Palmer, feel free to drop the maintainer addition. I just mostly want
> > to clean up my own mess on this when they decide to ratify more
> > extensions & this comes back up again.
> > ---
> >  Documentation/devicetree/bindings/riscv/cpus.yaml | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > index 873dd12f6e89..c0e0bc5dce04 100644
> > --- a/Documentation/devicetree/bindings/riscv/cpus.yaml
> > +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
> > @@ -9,6 +9,7 @@ title: RISC-V bindings for 'cpus' DT nodes
> >  maintainers:
> >    - Paul Walmsley <paul.walmsley@...ive.com>
> >    - Palmer Dabbelt <palmer@...ive.com>
> > +  - Conor Dooley <conor@...nel.org>
> >  
> >  description: |
> >    This document uses some terminology common to the RISC-V community
> > @@ -79,9 +80,7 @@ properties:
> >        insensitive, letters in the riscv,isa string must be all
> >        lowercase to simplify parsing.
> >      $ref: "/schemas/types.yaml#/definitions/string"
> > -    enum:
> > -      - rv64imac
> > -      - rv64imafdc
> > +    pattern: ^rv(?:64|32)imaf?d?q?c?b?v?k?h?(?:(?:_[zsh][imafdqcbvksh]|_x)(?:[a-z])+)*$

Actually we don't want S and H extensions to be treated like Z, but rather
like X. Only Z extensions have the category character convention. (And I'm
still tempted to just drop the enforcement from Z too, since it adds
additional maintenance and we've already settled for something less than
complete.)

Thanks,
drew

> >  
> >    # RISC-V requires 'timebase-frequency' in /cpus, so disallow it here
> >    timebase-frequency: false
> > -- 
> > 2.37.1
> >
> 
> Reviewed-by: Andrew Jones <ajones@...tanamicro.com>