[PATCH v2 2/2] x86/mwait-idle: add core C6 optimization for SPR

[Jan Beulich <jbeulich@suse.com>]

From: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

Add a Sapphire Rapids Xeon C6 optimization, similar to what we have for Sky Lake
Xeon: if package C6 is disabled, adjust C6 exit latency and target residency to
match core C6 values, instead of using the default package C6 values.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Origin: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 3a9cf77b60dc

Make sure a contradictory "preferred-cstates" wouldn't cause bypassing
of the added logic.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
---
v2: Sync with the Linux side fix to the noticed issue. Re-base over
    change to earlier patch.

--- a/xen/arch/x86/cpu/mwait-idle.c
+++ b/xen/arch/x86/cpu/mwait-idle.c
@@ -1273,18 +1273,31 @@ static void __init skx_idle_state_table_
  */
 static void __init spr_idle_state_table_update(void)
 {
-	/* Check if user prefers C1E over C1. */
-	if (preferred_states_mask & BIT(2, U)) {
-		if (preferred_states_mask & BIT(1, U))
-			/* Both can't be enabled, stick to the defaults. */
-			return;
+	uint64_t msr;
 
+	/* Check if user prefers C1E over C1. */
+	if (preferred_states_mask & BIT(2, U) &&
+	    !(preferred_states_mask & BIT(1, U))) {
+		/* Disable C1 and enable C1E. */
 		spr_cstates[0].flags |= CPUIDLE_FLAG_DISABLED;
 		spr_cstates[1].flags &= ~CPUIDLE_FLAG_DISABLED;
 
 		/* Request enabling C1E using the "C1E promotion" bit. */
 		idle_cpu_spr.c1e_promotion = C1E_PROMOTION_ENABLE;
 	}
+
+	/*
+	 * By default, the C6 state assumes the worst-case scenario of package
+	 * C6. However, if PC6 is disabled, we update the numbers to match
+	 * core C6.
+	 */
+	rdmsrl(MSR_PKG_CST_CONFIG_CONTROL, msr);
+
+	/* Limit value 2 and above allow for PC6. */
+	if ((msr & 0x7) < 2) {
+		spr_cstates[2].exit_latency = 190;
+		spr_cstates[2].target_residency = 600;
+	}
 }
 
 /*