Re: [PATCH v4 04/11] cpufreq: amd-pstate: add debug message while CPPC is supported and disabled by SBIOS

Mario Limonciello
2024-06-18T19:25:15Z

On 6/17/2024 01:59, Perry Yuan wrote:
> If CPPC feature is supported by the CPU however the CPUID flag bit is not
> set by SBIOS, the `amd_pstate` will be failed to load while system
> booting.
> So adding one more debug message to inform user to check the SBIOS setting,
> The change also can help maintainers to debug why amd_pstate driver failed
> to be loaded at system booting if the processor support CPPC.
>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218686
> Signed-off-by: Perry Yuan <perry.yuan@amd.com>
> Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>

Acked-by: Mario Limonciello <mario.limonciello@amd.com>

> ---
> drivers/cpufreq/amd-pstate.c | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 76419762c04f..9aa220a0e3fe 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -1749,11 +1749,37 @@ static int __init amd_pstate_set_driver(int mode_idx)
> */
> static bool amd_cppc_supported(void)
> {
> + struct cpuinfo_x86 *c = &cpu_data(0);
> + bool warn = false;
> +
> if ((boot_cpu_data.x86 == 0x17) && (boot_cpu_data.x86_model < 0x30)) {
> pr_debug_once("CPPC feature is not supported by the processor\n");
> return false;
> }
>
> + /*
> + * 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)) {
> + if (c->x86_model > 0x60 && c->x86_model < 0xaf)
> + warn = true;
> + } else if (cpu_feature_enabled(X86_FEATURE_ZEN3) || cpu_feature_enabled(X86_FEATURE_ZEN4)) {
> + if ((c->x86_model > 0x10 && c->x86_model < 0x1F) ||
> + (c->x86_model > 0x40 && c->x86_model < 0xaf))
> + warn = true;
> + } else if (cpu_feature_enabled(X86_FEATURE_ZEN5)) {
> + warn = true;
> + }
> + }
> +
> + 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 true;
> }
>