cpufreq: amd-pstate: auto-load pstate driver by default

If the `amd-pstate` driver is not loaded automatically by default,
it is because the kernel command line parameter has not been added.
To resolve this issue, it is necessary to call the `amd_pstate_set_driver()`
function to enable the desired mode (passive/active/guided) before registering
the driver instance.

This ensures that the driver is loaded correctly without relying on the kernel
command line parameter.

When there is no parameter added to command line, Kernel config will
provide the default mode to load.

Meanwhile, user can add driver mode in command line which will override
the kernel config default option.

Reported-by: Andrei Amuraritei <[email protected]>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218705
Signed-off-by: Perry Yuan <[email protected]>
Reviewed-by: Mario Limonciello <[email protected]>
Link: https://lore.kernel.org/r/83301c4cea4f92fb19e14b23f2bac7facfd8bdbb.1718811234.git.perry.yuan@amd.com
Signed-off-by: Mario Limonciello <[email protected]>

Author: Perry Yuan

drivers/cpufreq/amd-pstate.c

@@ -1801,8 +1801,13 @@ static int __init amd_pstate_init(void)
 	/* check if this machine need CPPC quirks */
 	dmi_check_system(amd_pstate_quirks_table);
 
-	switch (cppc_state) {
-	case AMD_PSTATE_UNDEFINED:
+	/*
+	* determine the driver mode from the command line or kernel config.
+	* If no command line input is provided, cppc_state will be AMD_PSTATE_UNDEFINED.
+	* command line options will override the kernel config settings.
+	*/
+
+	if (cppc_state == AMD_PSTATE_UNDEFINED) {
 		/* Disable on the following configs by default:
 		 * 1. Undefined platforms
 		 * 2. Server platforms
@@ -1812,15 +1817,20 @@ static int __init amd_pstate_init(void)
 			pr_info("driver load is disabled, boot with specific mode to enable this\n");
 			return -ENODEV;
 		}
-		ret = amd_pstate_set_driver(CONFIG_X86_AMD_PSTATE_DEFAULT_MODE);
-		if (ret)
-			return ret;
-		break;
+		/* get driver mode from kernel config option [1:4] */
+		cppc_state = CONFIG_X86_AMD_PSTATE_DEFAULT_MODE;
+	}
+
+	switch (cppc_state) {
 	case AMD_PSTATE_DISABLE:
+		pr_info("driver load is disabled, boot with specific mode to enable this\n");
 		return -ENODEV;
 	case AMD_PSTATE_PASSIVE:
 	case AMD_PSTATE_ACTIVE:
 	case AMD_PSTATE_GUIDED:
+		ret = amd_pstate_set_driver(cppc_state);
+		if (ret)
+			return ret;
 		break;
 	default:
 		return -EINVAL;
@@ -1841,7 +1851,7 @@ static int __init amd_pstate_init(void)
 	/* enable amd pstate feature */
 	ret = amd_pstate_enable(true);
 	if (ret) {
-		pr_err("failed to enable with return %d\n", ret);
+		pr_err("failed to enable driver mode(%d)\n", cppc_state);
 		return ret;
 	}