[Regression] 6.11.0-rc1: AMD CPU boot with error when CPPC feature disabled by BIOS

[David Wang <00107082@163.com>]

Hi,

I notice some kernel warning and errors when I update to 6.11.0-rc1:

 kernel: [    1.022739] amd_pstate: The CPPC feature is supported but currently disabled by the BIOS.
 kernel: [    1.022739] Please enable it if your BIOS has the CPPC option.
 kernel: [    1.098054] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
 kernel: [    1.110058] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
 kernel: [    1.122057] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
 kernel: [    1.134062] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
 kernel: [    1.134641] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
 kernel: [    1.135128] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
 kernel: [    1.135693] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
 kernel: [    1.136371] amd_pstate: min_freq(0) or max_freq(0) or nominal_freq(0) value is incorrect
 kernel: [    1.136390] amd_pstate: failed to register with return -19
 kernel: [    1.138410] ledtrig-cpu: registered to indicate activity on CPUs


Those warning message was introduced by commit:
 bff7d13c190ad98cf4f877189b022c75df4cb383 ("cpufreq: amd-pstate: add debug message while CPPC is supported and disabled by SBIOS)
, which make sense.

Those error message was introduced by commit:
 8f8b42c1fcc939a73b547b172a9ffcb65ef4bf47 ("cpufreq: amd-pstate: optimize the initial frequency values verification")
, when CPPC is disabled by BIOS, this error message does not make sense, and the error return-code would abort the driver registeration,
but this behavior could be handled earlier when detecting CPPC feature.

I feel following changes would make a clean fix: do not register amd_pstate driver when CPPC disabled by BIOS.

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 68c616b572f2..b06faea58fd4 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -1837,8 +1837,6 @@ static bool amd_cppc_supported(void)
         * If the CPPC feature is disabled in the BIOS for processors that support MSR-based CPPC,
         * the AMD Pstate driver may not function correctly.
         * Check the CPPC flag and display a warning message if the platform supports CPPC.
-        * Note: below checking code will not abort the driver registeration process because of
-        * the code is added for debugging purposes.
         */
        if (!cpu_feature_enabled(X86_FEATURE_CPPC)) {
                if (cpu_feature_enabled(X86_FEATURE_ZEN1) || cpu_feature_enabled(X86_FEATURE_ZEN2)) {
@@ -1856,6 +1854,7 @@ static bool amd_cppc_supported(void)
        if (warn)
                pr_warn_once("The CPPC feature is supported but currently disabled by the BIOS.\n"
                                        "Please enable it if your BIOS has the CPPC option.\n");
+               return false;
        return true;
 }



Thanks
David