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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