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

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Message-Id: <20220817200531.988850-4-mail@conchuod.ie>
Date:   Wed, 17 Aug 2022 21:05:22 +0100
From:   Conor Dooley <mail@...chuod.ie>
To:     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>
Cc:     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>,
        Andrew Jones <ajones@...tanamicro.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: [PATCH 3/4] dt-bindings: riscv: add new riscv,isa strings for emulators

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.
     $ref: "/schemas/types.yaml#/definitions/string"
-    enum:
-      - rv64imac
-      - rv64imafdc
+    pattern: ^rv(?:64|32)imaf?d?q?c?b?v?k?h?(?:(?:_[zsh][imafdqcbvksh]|_x)(?:[a-z])+)*$
 
   # RISC-V requires 'timebase-frequency' in /cpus, so disallow it here
   timebase-frequency: false
-- 
2.37.1