Re: [PATCH v8 12/22] RISC-V: perf: Modify the counter discovery mechanism

On 7/20/26 12:21 AM, Charlie Jenkins wrote:
> On Wed, 01 Jul 2026 01:47:00 -0700, Atish Patra <[email protected]> wrote:
>> diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
>> index 74d934238821..c20f1e33c65d 100644
>> --- a/drivers/perf/riscv_pmu_sbi.c
>> +++ b/drivers/perf/riscv_pmu_sbi.c
>> @@ -1599,13 +1658,23 @@ static int __init rvpmu_devinit(void)
>> [ ... skip 15 lines ... ]
>> +	 * in S-mode via Supervisor Counter delegation.
>> +	 */
>> +	if (riscv_isa_extension_available(NULL, SSCCFG) &&
>> +	    riscv_isa_extension_available(NULL, SMCDELEG) &&
>> +	    riscv_isa_extension_available(NULL, SSCSRIND))
>> +		static_branch_enable(&riscv_pmu_cdeleg_available);
> This needs to not only check that smcdeleg is supported in linux, but
> also that it is supported in the SBI implementation correct? Trying to
> boot this on OpenSBI before 6bb6b61c27eb ("lib: sbi: Add support for smcsrind and
> smcdeleg") will fail on an illegal instruction in
> rvpmu_deleg_find_ctrs() while trying to access the scountinhibit csr in
> the patch "RISC-V: perf: Implement supervisor counter delegation
> support". The proper mstateen bits need to be set for this to work
> without crashing.

Yeah. We can do trap/detect to identify if smcdeleg is actually 
available but that is bit ugly.
The firmware should make sure that it doesn't advertises an ISA 
extension if that is not avaialble
to S-mode but that model only works for newer firmware.

if you are running very old firmware with new Qemu/platform, the default 
ISA extension may have
smcdeleg while older firmware may not even know about it.

In reality, I am hoping chances of that happening are rare as OpenSBI 
patches have been available
from a long time and Linux kernel patches are yet to merge. I have not 
addressed this in v9 as I am
not sure which is the best worst approach yet :)

>