From: Rafael J. Wysocki rafael.j.wysocki@intel.com
commit e5af36b2adb858e982d78d41d7363d05d951a19a upstream.
It turns out that there are systems where HWP is enabled during initialization by the platform firmware (BIOS), but HWP EPP support is not advertised.
After commit 7aa1031223bc ("cpufreq: intel_pstate: Avoid enabling HWP if EPP is not supported") intel_pstate refuses to use HWP on those systems, but the fallback PERF_CTL interface does not work on them either because of enabled HWP, and once enabled, HWP cannot be disabled. Consequently, the users of those systems cannot control CPU performance scaling.
Address this issue by making intel_pstate use HWP unconditionally if it is enabled already when the driver starts.
Fixes: 7aa1031223bc ("cpufreq: intel_pstate: Avoid enabling HWP if EPP is not supported") Reported-by: Srinivas Pandruvada srinivas.pandruvada@linux.intel.com Tested-by: Srinivas Pandruvada srinivas.pandruvada@linux.intel.com Signed-off-by: Rafael J. Wysocki rafael.j.wysocki@intel.com Cc: 5.9+ stable@vger.kernel.org # 5.9+ Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/cpufreq/intel_pstate.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)
--- a/drivers/cpufreq/intel_pstate.c +++ b/drivers/cpufreq/intel_pstate.c @@ -3054,6 +3054,14 @@ static const struct x86_cpu_id hwp_suppo {} };
+static bool intel_pstate_hwp_is_enabled(void) +{ + u64 value; + + rdmsrl(MSR_PM_ENABLE, value); + return !!(value & 0x1); +} + static int __init intel_pstate_init(void) { const struct x86_cpu_id *id; @@ -3072,8 +3080,12 @@ static int __init intel_pstate_init(void * Avoid enabling HWP for processors without EPP support, * because that means incomplete HWP implementation which is a * corner case and supporting it is generally problematic. + * + * If HWP is enabled already, though, there is no choice but to + * deal with it. */ - if (!no_hwp && boot_cpu_has(X86_FEATURE_HWP_EPP)) { + if ((!no_hwp && boot_cpu_has(X86_FEATURE_HWP_EPP)) || + intel_pstate_hwp_is_enabled()) { hwp_active++; hwp_mode_bdw = id->driver_data; intel_pstate.attr = hwp_cpufreq_attrs;