Re: [PATCH v4 05/16] riscv: Extend cpufeature.c to detect vendor extensions

Charlie Jenkins
2024-05-01T17:06:22Z

On Wed, May 01, 2024 at 12:19:34PM +0100, Conor Dooley wrote:
> On Fri, Apr 26, 2024 at 02:29:19PM -0700, Charlie Jenkins wrote:
> > @@ -353,6 +336,10 @@ static void __init riscv_parse_isa_string(unsigned long *this_hwcap, struct risc
> > bool ext_long = false, ext_err = false;
> >
> > switch (*ext) {
> > + case 'x':
> > + case 'X':
> > + pr_warn_once("Vendor extensions are ignored in riscv,isa. Use riscv,isa-extensions instead.");
> > + continue;
>
> Yeah, so this is not right - you need to find the end of the extension
> before containing - for example if I had a system with
> rv64imafdcxconorkwe, you get something like:
> [ 0.000000] CPU with hartid=0 is not available
> [ 0.000000] Falling back to deprecated "riscv,isa"
> [ 0.000000] Vendor extensions are ignored in riscv,isa. Use riscv,isa-extensions instead.
> [ 0.000000] riscv: base ISA extensions acdefikmnorw
> [ 0.000000] riscv: ELF capabilities acdfim
>
> kwe are all pretty safe letters, but suppose one was a v..
> I think you can just yoink the code from the s/z case:

Oh right, I forgot about that.

>
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 20bc9ba6b7a2..4daedba7961f 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -338,8 +338,19 @@ static void __init riscv_parse_isa_string(unsigned long *this_hwcap, struct risc
> switch (*ext) {
> case 'x':
> case 'X':
> - pr_warn_once("Vendor extensions are ignored in riscv,isa. Use riscv,isa-extensions instead.");
> - continue;
> + if (acpi_disabled)
> + pr_warn_once("Vendor extensions are ignored in riscv,isa. Use riscv,isa-extensions instead.");
> + /*
> + * To skip an extension, we find its end.
> + * As multi-letter extensions must be split from other multi-letter
> + * extensions with an "_", the end of a multi-letter extension will
> + * either be the null character or the "_" at the start of the next
> + * multi-letter extension.
> + */
> + for (; *isa && *isa != '_'; ++isa)
> + ;
> + ext_err = true;
> + break;
> case 's':
> /*
> * Workaround for invalid single-letter 's' & 'u' (QEMU).
>
> You'll note that I made the dt property error dt only, this function
> gets called for ACPI too. I think the skip is pretty safe there though
> at the moment, we've not established any meanings yet for vendor stuff
> on ACPI.
> I think breaking is probably better than using continue - we get the _
> skip from outside the switch statement out of that. And ye, I am lazy
> so I kept it as a for loop.

Awesome, thanks!

- Charlie

>
> Cheers,
> Conor.