[PATCH v3 04/10] cpufreq: amd-pstate: add debug message while CPPC is supported and disabled by SBIOS

[Perry Yuan]

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@xxxxxxx>
---
 drivers/cpufreq/amd-pstate.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index f166b3b94091..6b9fc24001f2 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -1746,11 +1746,36 @@ static int __init amd_pstate_set_driver(int mode_idx)
  */
 static bool amd_cppc_supported(void)
 {
+	struct cpuinfo_x86 *c = &cpu_data(0);
+
 	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.
+	 * Notice: below checking code will not abort the driver registeration process.
+	 */
+	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)
+				goto warn;
+		} 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))
+				goto warn;
+		} else if (cpu_feature_enabled(X86_FEATURE_ZEN5)) {
+			goto warn;
+		}
+	}
+
+	return true;
+
+warn:
+	pr_debug_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;
 }
 
-- 
2.34.1