intel_idle: clean up BYT/CHT auto demotion disable

JIRA: https://issues.redhat.com/browse/RHEL-85522

commit c93d13b
Author: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Date:   Mon Feb 10 09:12:53 2025 +0200

    intel_idle: clean up BYT/CHT auto demotion disable

    Bay Trail (BYT) and Cherry Trail (CHT) platforms have a very specific way
    of disabling auto-demotion via specific MSR bits. Clean up the code so that
    BYT/CHT-specifics do not show up in the common 'struct idle_cpu' data
    structure.

    Remove the 'byt_auto_demotion_disable_flag' flag from 'struct idle_cpu',
    because a better coding pattern is to avoid very case-specific fields like
    'bool byt_auto_demotion_disable_flag' in a common data structure, which is
    used for all platforms, not only BYT/CHT. The code is just more readable
    when common data structures contain only commonly used fields.

    Instead, match BYT/CHT in the 'intel_idle_init_cstates_icpu()' function,
    and introduce a small helper to take care of BYT/CHT auto-demotion. This
    is consistent with how platform-specific things are done for other
    platforms.

    No intended functional changes, compile-tested only.

    Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
    Link: https://patch.msgid.link/20250210071253.2991030-1-dedekind1@gmail.com
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Signed-off-by: David Arcari <darcari@redhat.com>

Author: darcari

drivers/idle/intel_idle.c

@@ -89,7 +89,6 @@ struct idle_cpu {
 	 * Indicate which enable bits to clear here.
 	 */
 	unsigned long auto_demotion_disable_flags;
-	bool byt_auto_demotion_disable_flag;
 	bool disable_promotion_to_c1e;
 	bool use_acpi;
 };
@@ -1472,13 +1471,11 @@ static const struct idle_cpu idle_cpu_snx __initconst = {
 static const struct idle_cpu idle_cpu_byt __initconst = {
 	.state_table = byt_cstates,
 	.disable_promotion_to_c1e = true,
-	.byt_auto_demotion_disable_flag = true,
 };
 
 static const struct idle_cpu idle_cpu_cht __initconst = {
 	.state_table = cht_cstates,
 	.disable_promotion_to_c1e = true,
-	.byt_auto_demotion_disable_flag = true,
 };
 
 static const struct idle_cpu idle_cpu_ivb __initconst = {
@@ -2065,6 +2062,15 @@ static void __init spr_idle_state_table_update(void)
 	}
 }
 
+/**
+ * byt_cht_auto_demotion_disable - Disable Bay/Cherry Trail auto-demotion.
+ */
+static void __init byt_cht_auto_demotion_disable(void)
+{
+	wrmsrl(MSR_CC6_DEMOTION_POLICY_CONFIG, 0);
+	wrmsrl(MSR_MC6_DEMOTION_POLICY_CONFIG, 0);
+}
+
 static bool __init intel_idle_verify_cstate(unsigned int mwait_hint)
 {
 	unsigned int mwait_cstate = (MWAIT_HINT2CSTATE(mwait_hint) + 1) &
@@ -2146,6 +2152,10 @@ static void __init intel_idle_init_cstates_icpu(struct cpuidle_driver *drv)
 	case INTEL_ATOM_GRACEMONT:
 		adl_idle_state_table_update();
 		break;
+	case INTEL_ATOM_SILVERMONT:
+	case INTEL_ATOM_AIRMONT:
+		byt_cht_auto_demotion_disable();
+		break;
 	}
 
 	for (cstate = 0; cstate < CPUIDLE_STATE_MAX; ++cstate) {
@@ -2191,11 +2201,6 @@ static void __init intel_idle_init_cstates_icpu(struct cpuidle_driver *drv)
 
 		drv->state_count++;
 	}
-
-	if (icpu->byt_auto_demotion_disable_flag) {
-		wrmsrl(MSR_CC6_DEMOTION_POLICY_CONFIG, 0);
-		wrmsrl(MSR_MC6_DEMOTION_POLICY_CONFIG, 0);
-	}
 }
 
 /**