[PATCH v3 3/8] cpufreq: amd-pstate: change driver to be built-in type

[Perry Yuan <Perry.Yuan@amd.com>]

Change the `amd-pstate` driver as the built-in type which can help to
load the driver before the acpi_cpufreq driver as the default pstate
driver for the AMD processors.

for the processors do not have the dedicated MSR functions, add
`amd-pstate=legacy_cppc` to grub which enable shared memmory interface
to communicate with cppc_acpi module to control pstate hints.

Signed-off-by: Perry Yuan <Perry.Yuan@amd.com>
---
 drivers/cpufreq/amd-pstate.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index ace7d50cf2ac..14906431dc15 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -59,10 +59,7 @@
  * we disable it by default to go acpi-cpufreq on these processors and add a
  * module parameter to be able to enable it manually for debugging.
  */
-static bool shared_mem = false;
-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 shared_mem __read_mostly;
 
 static struct cpufreq_driver amd_pstate_driver;
 
@@ -653,16 +650,22 @@ static int __init amd_pstate_init(void)
 
 	return ret;
 }
+device_initcall(amd_pstate_init);
 
-static void __exit amd_pstate_exit(void)
+static int __init amd_pstate_param(char *str)
 {
-	cpufreq_unregister_driver(&amd_pstate_driver);
+	if (!str)
+		return -EINVAL;
 
-	amd_pstate_enable(false);
-}
+	/* enable shared memory type CPPC ,if you processor has no MSR, you have to add this
+	 * to your grub to make cppc driver loaded successfully.
+	 */
+	if (!strcmp(str, "legacy_cppc"))
+		shared_mem = true;
 
-module_init(amd_pstate_init);
-module_exit(amd_pstate_exit);
+	return 0;
+}
+early_param("amd-pstate", amd_pstate_param);
 
 MODULE_AUTHOR("Huang Rui <ray.huang@amd.com>");
 MODULE_DESCRIPTION("AMD Processor P-state Frequency Driver");
-- 
2.34.1