[PATCH for-4.22 v2 2/8] x86/mwait-idle: clean up BYT/CHT auto demotion disable

[Jan Beulich <jbeulich@suse.com>]

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.

Inspired by (and description largely taken from) Linux'es c93d13b661a6
("intel_idle: clean up BYT/CHT auto demotion disable").

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
v2: Init "first" to "true" in mwait_idle_cpu_init().

--- a/xen/arch/x86/cpu/mwait-idle.c
+++ b/xen/arch/x86/cpu/mwait-idle.c
@@ -103,7 +103,6 @@ struct idle_cpu {
 	 * Indicate which enable bits to clear here.
 	 */
 	unsigned long auto_demotion_disable_flags;
-	bool byt_auto_demotion_disable_flag;
 	enum c1e_promotion c1e_promotion;
 };
 
@@ -1144,7 +1143,7 @@ static void cf_check auto_demotion_disab
 	wrmsrl(MSR_PKG_CST_CONFIG_CONTROL, msr_bits);
 }
 
-static void cf_check byt_auto_demotion_disable(void *dummy)
+static void byt_cht_auto_demotion_disable(void)
 {
 	wrmsrl(MSR_CC6_DEMOTION_POLICY_CONFIG, 0);
 	wrmsrl(MSR_MC6_DEMOTION_POLICY_CONFIG, 0);
@@ -1195,13 +1194,11 @@ static const struct idle_cpu idle_cpu_sn
 static const struct idle_cpu idle_cpu_byt = {
 	.state_table = byt_cstates,
 	.c1e_promotion = C1E_PROMOTION_DISABLE,
-	.byt_auto_demotion_disable_flag = true,
 };
 
 static const struct idle_cpu idle_cpu_cht = {
 	.state_table = cht_cstates,
 	.c1e_promotion = C1E_PROMOTION_DISABLE,
-	.byt_auto_demotion_disable_flag = true,
 };
 
 static const struct idle_cpu idle_cpu_ivb = {
@@ -1677,14 +1674,11 @@ static int __init mwait_idle_probe(void)
 	return 0;
 }
 
-static void mwait_idle_cpu_tweak(unsigned int cpu)
+static void mwait_idle_cpu_tweak(unsigned int cpu, bool bsp)
 {
 	if (icpu->auto_demotion_disable_flags)
 		on_selected_cpus(cpumask_of(cpu), auto_demotion_disable, NULL, 1);
 
-	if (icpu->byt_auto_demotion_disable_flag)
-		on_selected_cpus(cpumask_of(cpu), byt_auto_demotion_disable, NULL, 1);
-
 	switch (icpu->c1e_promotion) {
 	case C1E_PROMOTION_DISABLE:
 		on_selected_cpus(cpumask_of(cpu), c1e_promotion_disable, NULL, 1);
@@ -1697,12 +1691,24 @@ static void mwait_idle_cpu_tweak(unsigne
 	case C1E_PROMOTION_PRESERVE:
 		break;
 	}
+
+	/* Pkg-scope MSRs on 1-socket-only systems need writing only once. */
+	if (!bsp)
+		return;
+
+	switch (boot_cpu_data.vfm) {
+	case INTEL_ATOM_SILVERMONT:
+	case INTEL_ATOM_AIRMONT:
+		byt_cht_auto_demotion_disable();
+		break;
+	}
 }
 
 static int cf_check mwait_idle_cpu_init(
     struct notifier_block *nfb, unsigned long action, void *hcpu)
 {
 	unsigned int cpu = (unsigned long)hcpu, cstate;
+	static bool first = true;
 	struct acpi_processor_power *dev = processor_powers[cpu];
 
 	switch (action) {
@@ -1781,7 +1787,8 @@ static int cf_check mwait_idle_cpu_init(
 		dev->count++;
 	}
 
-	mwait_idle_cpu_tweak(cpu);
+	mwait_idle_cpu_tweak(cpu, first);
+	first = false;
 
 	return NOTIFY_DONE;
 }
@@ -1818,7 +1825,7 @@ void mwait_idle_resume(void)
 	if (!icpu)
 		return;
 
-	mwait_idle_cpu_tweak(smp_processor_id());
+	mwait_idle_cpu_tweak(smp_processor_id(), true);
 }
 
 /* Helper function for HPET. */