[PATCH 02/11] cpufreq: amd-pstate: show CPPC debug message if CPPC is not supported

[Perry Yuan]

Add CPU ID checking in case the driver attempt to load on systems where
CPPC functionality is unavailable. And the warning message will not
be showed if CPPC is not supported.

It will also print debug message if the CPU has no CPPC support that
helps to debug the driver loading failure issue.

Closes: https://lore.kernel.org/linux-pm/CYYPR12MB8655D32EA18574C9497E888A9C122@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/T/#t
Signed-off-by: Perry Yuan <perry.yuan@xxxxxxx>
---
 drivers/cpufreq/amd-pstate.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index be7f2d3c86b6..cb766c061c86 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -1687,6 +1687,20 @@ static int __init amd_pstate_set_driver(int mode_idx)
 	return -EINVAL;
 }
 
+/**
+ * CPPC function is not supported for family ID 17H with model_ID ranging from 0x10 to 0x2F.
+ * show the debug message that helps to check if the CPU has CPPC support for loading issue.
+ */
+static bool amd_cppc_supported(void)
+{
+	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;
+	}
+
+	return true;
+}
+
 static int __init amd_pstate_init(void)
 {
 	struct device *dev_root;
@@ -1695,6 +1709,11 @@ static int __init amd_pstate_init(void)
 	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
 		return -ENODEV;
 
+	/* show debug message only if CPPC is not supported */
+	if (!amd_cppc_supported())
+		return -EOPNOTSUPP;
+
+	/* show warning message when BIOS broken or ACPI disabled */
 	if (!acpi_cpc_valid()) {
 		pr_warn_once("the _CPC object is not present in SBIOS or ACPI disabled\n");
 		return -ENODEV;
-- 
2.34.1