amd-pstate: Set min_perf to nominal_perf for active mode performance gov

The amd-pstate driver sets CPPC_REQ.min_perf to CPPC_REQ.max_perf when
in active mode with performance governor. Typically CPPC_REQ.max_perf
is set to CPPC.highest_perf. This causes frequency throttling on
power-limited platforms which causes performance regressions on
certain classes of workloads.

Hence, set the CPPC_REQ.min_perf to the CPPC.nominal_perf or
CPPC_REQ.max_perf, whichever is lower of the two.

Fixes: ffa5096 ("cpufreq: amd-pstate: implement Pstate EPP support for the AMD processors")
Signed-off-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://lore.kernel.org/r/20241021101836.9047-2-gautham.shenoy@amd.com
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>

Author: gautshen

drivers/cpufreq/amd-pstate.c

@@ -1535,7 +1535,7 @@ static int amd_pstate_epp_update_limit(struct cpufreq_policy *policy)
 	value = READ_ONCE(cpudata->cppc_req_cached);
 
 	if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE)
-		min_perf = max_perf;
+		min_perf = min(cpudata->nominal_perf, max_perf);
 
 	/* Initial min/max values for CPPC Performance Controls Register */
 	value &= ~AMD_CPPC_MIN_PERF(~0L);