amd-pstate: Switch to amd-pstate by default on some Server platforms

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 <[email protected]>
Signed-off-by: Gautham R. Shenoy <[email protected]>
Reviewed-by: Mario Limonciello <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Mario Limonciello <[email protected]>

Author: SSapkal

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;
 		}