Re: [PATCH v1] cpufreq: intel_pstate: Skip HWP_CAP reads in Broadwell mode

[Chen, Yu C]

Hi Rafael,

On 6/20/2026 3:24 AM, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>
> When running in the Broadwell HWP mode, the turbo, max and min
> P-state values are retrieved from MSR_PLATFORM_INFO, so reading
> MSR_HWP_CAPABILITIES in that mode in order to update those values
> is pointless.  Moreover, using the MSR_HWP_CAPABILITIES value for
> updating them in the Broadwell mode may be harmful, so avoid doing
> that altogether.
>
> Fixes: de5bcf404ace ("cpufreq: intel_pstate: Clean up frequency computations")

sashiko[1] reports an issue that hwp_cap_cached remains 0.
Maybe still use the value from MSR_HWP_CAPABILITIES for cached value,
which was what we did before commit de5bcf404ace? I fed this
to AI and was given the following:

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 5a0eeb84d382..a373a199c9c6 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -1189,6 +1189,8 @@ static void __intel_pstate_get_hwp_cap(struct 
cpudata *cpu)

     rdmsrq_on_cpu(cpu->cpu, MSR_HWP_CAPABILITIES, &cap);
     WRITE_ONCE(cpu->hwp_cap_cached, cap);
+	if (hwp_mode_bdw)
+		return;
     cpu->pstate.max_pstate = HWP_GUARANTEED_PERF(cap);
     cpu->pstate.turbo_pstate = HWP_HIGHEST_PERF(cap);
 }
@@ -1199,6 +1201,9 @@ static void intel_pstate_get_hwp_cap(struct 
cpudata *cpu)

     __intel_pstate_get_hwp_cap(cpu);

+	if (hwp_mode_bdw)
+		return;
+
     cpu->pstate.max_freq = cpu->pstate.max_pstate * scaling;
     cpu->pstate.turbo_freq = cpu->pstate.turbo_pstate * scaling;
     if (scaling != cpu->pstate.perf_ctl_scaling) {


[1] https://sashiko.dev/#/patchset/12920597.O9o76ZdvQC%40rafael.j.wysocki

thanks,
Chenyu