[PATCH v4 3/4] dt-bindings: riscv: add new riscv,isa strings for emulators

Conor Dooley
2022-08-23T18:34:18Z

From: Conor Dooley <conor.dooley@microchip.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:
- ima are required
- 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
- convention says that 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
- as the above is just convention, don't apply any charset restrictions
to reduce future churn
- 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

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@kernel.org>
Link: https://lore.kernel.org/linux-riscv/20220803170552.GA2250266-robh@kernel.org/
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Acked-by: Guo Ren <guoren@kernel.org>
Signed-off-by: Conor Dooley <conor.dooley@microchip.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..90a7cabf58fe 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@sifive.com>
- Palmer Dabbelt <palmer@sifive.com>
+ - Conor Dooley <conor@kernel.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.
$ref: "/schemas/types.yaml#/definitions/string"
- enum:
- - rv64imac
- - rv64imafdc
+ pattern: ^rv(?:64|32)imaf?d?q?c?b?v?k?h?(?:_[hsxz](?:[a-z])+)*$

# RISC-V requires 'timebase-frequency' in /cpus, so disallow it here
timebase-frequency: false
--
2.37.1