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dt-bindings: riscv: add new riscv,isa strings for emulators
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: