[PATCH] amd-pstate: Fix amd_pstate mode switch

[Wyes Karny <wyes.karny@amd.com>]

amd_pstate mode can be changed by writing the mode name to the `status`
sysfs. But some combinations are not working. Fix this issue by taking
care of the edge cases.

Before the fix the mode change combination test fails:

 #./pst_test.sh
Test passed: from: disable, to
Test passed: from: disable, to disable
Test failed: 1, From mode: disable, to mode: passive
Test failed: 1, From mode: disable, to mode: active
Test failed: 1, From mode: passive, to mode: active
Test passed: from: passive, to disable
Test failed: 1, From mode: passive, to mode: passive
Test failed: 1, From mode: passive, to mode: active
Test failed: 1, From mode: active, to mode: active
Test passed: from: active, to disable
Test failed: 1, From mode: active, to mode: passive
Test failed: 1, From mode: active, to mode: active

After the fix test passes:

 #./pst_test.sh
Test passed: from: disable, to
Test passed: from: disable, to disable
Test passed: from: disable, to passive
Test passed: from: disable, to active
Test passed: from: passive, to active
Test passed: from: passive, to disable
Test passed: from: passive, to passive
Test passed: from: passive, to active
Test passed: from: active, to active
Test passed: from: active, to disable
Test passed: from: active, to passive
Test passed: from: active, to active

Fixes: abd61c08ef349 ("cpufreq: amd-pstate: add driver working mode switch support")

Acked-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Alexey Kardashevskiy <aik@amd.com>
Signed-off-by: Wyes Karny <wyes.karny@amd.com>

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Perry Yuan <Perry.Yuan@amd.com>

---
 drivers/cpufreq/amd-pstate.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 73c7643b2697..8dd46fad151e 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -840,22 +840,20 @@ static int amd_pstate_update_status(const char *buf, size_t size)
 
 	switch(mode_idx) {
 	case AMD_PSTATE_DISABLE:
-		if (!current_pstate_driver)
-			return -EINVAL;
-		if (cppc_state == AMD_PSTATE_ACTIVE)
-			return -EBUSY;
-		cpufreq_unregister_driver(current_pstate_driver);
-		amd_pstate_driver_cleanup();
+		if (current_pstate_driver) {
+			cpufreq_unregister_driver(current_pstate_driver);
+			amd_pstate_driver_cleanup();
+		}
 		break;
 	case AMD_PSTATE_PASSIVE:
 		if (current_pstate_driver) {
 			if (current_pstate_driver == &amd_pstate_driver)
 				return 0;
 			cpufreq_unregister_driver(current_pstate_driver);
-			cppc_state = AMD_PSTATE_PASSIVE;
-			current_pstate_driver = &amd_pstate_driver;
 		}
 
+		current_pstate_driver = &amd_pstate_driver;
+		cppc_state = AMD_PSTATE_PASSIVE;
 		ret = cpufreq_register_driver(current_pstate_driver);
 		break;
 	case AMD_PSTATE_ACTIVE:
@@ -863,10 +861,10 @@ static int amd_pstate_update_status(const char *buf, size_t size)
 			if (current_pstate_driver == &amd_pstate_epp_driver)
 				return 0;
 			cpufreq_unregister_driver(current_pstate_driver);
-			current_pstate_driver = &amd_pstate_epp_driver;
-			cppc_state = AMD_PSTATE_ACTIVE;
 		}
 
+		current_pstate_driver = &amd_pstate_epp_driver;
+		cppc_state = AMD_PSTATE_ACTIVE;
 		ret = cpufreq_register_driver(current_pstate_driver);
 		break;
 	default:
-- 
2.34.1