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

Conor Dooley
2024-05-01T11:19:41Z

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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:

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.

Cheers,
Conor.

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