[PATCH 2/2] amd-pstate: Switch to amd-pstate by default on some Server platforms

["Gautham R. Shenoy" <gautham.shenoy@amd.com>]

From: Swapnil Sapkal <swapnil.sapkal@amd.com>

Currently the default cpufreq driver for all the AMD EPYC servers is
acpi-cpufreq. Going forward, switch to amd-pstate as the default
driver on the AMD EPYC server platforms with CPU family 0x1A or
higher. The default mode will be active mode.

Testing shows that amd-pstate with active mode and performance
governor provides comparable or better performance per-watt against
acpi-cpufreq + performance governor.

Likewise, amd-pstate with active mode and powersave governor with the
energy_performance_preference=power (EPP=255) provides comparable or
better performance per-watt against acpi-cpufreq + schedutil governor
for a wide range of workloads.

Users can still revert to using acpi-cpufreq driver on these platforms
with the "amd_pstate=disable" kernel commandline parameter.

Signed-off-by: Swapnil Sapkal <swapnil.sapkal@amd.com>
Signed-off-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
---
 drivers/cpufreq/amd-pstate.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 23349f50c83e..3c14962adeb2 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -1832,10 +1832,10 @@ static int __init amd_pstate_init(void)
 	if (cppc_state == AMD_PSTATE_UNDEFINED) {
 		/* Disable on the following configs by default:
 		 * 1. Undefined platforms
-		 * 2. Server platforms
+		 * 2. Server platforms with CPUs older than Family 0x1A.
 		 */
 		if (amd_pstate_acpi_pm_profile_undefined() ||
-		    amd_pstate_acpi_pm_profile_server()) {
+		    (amd_pstate_acpi_pm_profile_server() && boot_cpu_data.x86 < 0x1A)) {
 			pr_info("driver load is disabled, boot with specific mode to enable this\n");
 			return -ENODEV;
 		}
-- 
2.34.1