[PATCH 2/2] RISC-V: fix the comment for ISA string workaround

[Conor Dooley]

On Sat, Jul 22, 2023 at 06:22:38AM +0000, Tsukasa OI wrote:
> From: Tsukasa OI <research_trasio at irq.a4lg.com>
> 
> Extensions prefixed with "Su" won't corrupt the workaround in many
> cases.  The only exception is when the first multi-letter extension in the
> ISA string begins with "Su" and is not prefixed with an underscore.
> 
> For instance, following ISA string can confuse this QEMU workaround.
> 
> *   "rv64imacsuclic" (RV64I + M + A + C + "Suclic")
> 
> However, this case is very unlikely because extensions prefixed by either
> "Z", "Sm" or "Ss" will most likely precede first.
> 
> For instance, the "Suclic" extension (draft as of now) will be placed after
> related "Smclic" and "Ssclic" extensions.  It's also highly likely that
> other unprivileged extensions like "Zba" will precede.
> 
> It's also possible to suppress the issue in the QEMU workaround with an
> underscore.  Following ISA string won't confuse the QEMU workaround.
> 
> *   "rv64imac_suclic" (RV64I + M + A + C + delimited "Suclic")
> 
> This fix is to tell kernel developers the nature of this workaround
> precisely.  There are some "Su*" extensions to be ratified but don't worry
> about this workaround too much.
> 

> This commit comes with another minor editorial fix.

Which is what?

The new wording is fine by me though..
Reviewed-by: Conor Dooley <conor.dooley at microchip.com>

Thanks,
Conor.

> Signed-off-by: Tsukasa OI <research_trasio at irq.a4lg.com>
> ---
>  arch/riscv/kernel/cpufeature.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 63277cdc1ea5..91f1ef3e762c 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -170,10 +170,11 @@ void __init riscv_fill_hwcap(void)
>  			case 's':
>  			case 'S':
>  				/*
> -				 * Workaround for invalid single-letter 's' & 'u'(QEMU).
> -				 * No need to set the bit in riscv_isa as 's' & 'u' are
> -				 * not valid ISA extensions. It works until multi-letter
> -				 * extension starting with "Su" appears.
> +				 * Workaround for invalid single-letters 's' & 'u' (QEMU).
> +				 * No need to set the bits in riscv_isa as 's' and 'u' are
> +				 * not valid ISA extensions. It works unless the first multi-letter
> +				 * extension in the ISA string begins with "Su" and not prefixed
> +				 * with an underscore.
>  				 */
>  				if (ext[-1] != '_' && tolower(ext[1]) == 'u') {
>  					++isa;
> -- 
> 2.40.0
> 
> 
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