[PATCH 2/3] cpufreq: amd-pstate: Allow replacing existing cpufreq drivers when loaded

[Mario Limonciello <mario.limonciello@amd.com>]

`amd-pstate` can be compiled as a module.  This however can be a
deficiency because `acpi-cpufreq` will be loaded earlier when compiled
into the kernel meaning `amd-pstate` doesn't get a chance.
`acpi-cpufreq` is also unable to be unloaded in this circumstance.

To better improve the usability of `amd-pstate` when compiled as a module,
add an optional module parameter that will force it to replace other
cpufreq drivers at startup.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
 drivers/cpufreq/amd-pstate.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 9ce75ed11f8e..31a04e818195 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -63,6 +63,11 @@ module_param(shared_mem, bool, 0444);
 MODULE_PARM_DESC(shared_mem,
 		 "enable amd-pstate on processors with shared memory solution (false = disabled (default), true = enabled)");
 
+static bool replace = false;
+module_param(replace, bool, 0444);
+MODULE_PARM_DESC(replace,
+		  "replace other cpufreq drivers upon init if necessary");
+
 static struct cpufreq_driver amd_pstate_driver;
 
 /**
@@ -598,9 +603,11 @@ static int __init amd_pstate_init(void)
 		return -ENODEV;
 	}
 
-	/* don't keep reloading if cpufreq_driver exists */
-	if (cpufreq_get_current_driver())
-		return -EEXIST;
+	if (cpufreq_get_current_driver()) {
+		ret = replace ? cpufreq_unregister_driver(NULL) : -EEXIST;
+		if (ret)
+			return ret;
+	}
 
 	/* capability check */
 	if (boot_cpu_has(X86_FEATURE_CPPC)) {
-- 
2.34.1