intel_idle: Disable Baytrail Core and Module C6 auto-demotion

Power efficiency improves on Baytrail (Intel Atom Processor E3000)
when Linux disables C6 auto-demotion.

Based on work by Srinidhi Kasagar <srinidhi.kasagar@intel.com>.
Signed-off-by: Len Brown <len.brown@intel.com>
Cc: x86@kernel.org

arch/x86/include/uapi/asm/msr-index.h

@@ -149,6 +149,9 @@
 
 #define MSR_CORE_C1_RES			0x00000660
 
+#define MSR_CC6_DEMOTION_POLICY_CONFIG	0x00000668
+#define MSR_MC6_DEMOTION_POLICY_CONFIG	0x00000669
+
 #define MSR_AMD64_MC0_MASK		0xc0010044
 
 #define MSR_IA32_MCx_CTL(x)		(MSR_IA32_MC0_CTL + 4*(x))

drivers/idle/intel_idle.c

@@ -89,6 +89,7 @@ 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;
 };
 
@@ -613,6 +614,7 @@ static const struct idle_cpu idle_cpu_snb = {
 static const struct idle_cpu idle_cpu_byt = {
 	.state_table = byt_cstates,
 	.disable_promotion_to_c1e = true,
+	.byt_auto_demotion_disable_flag = true,
 };
 
 static const struct idle_cpu idle_cpu_ivb = {
@@ -814,6 +816,11 @@ static int __init intel_idle_cpuidle_driver_init(void)
 	if (icpu->auto_demotion_disable_flags)
 		on_each_cpu(auto_demotion_disable, NULL, 1);
 
+	if (icpu->byt_auto_demotion_disable_flag) {
+		wrmsrl(MSR_CC6_DEMOTION_POLICY_CONFIG, 0);
+		wrmsrl(MSR_MC6_DEMOTION_POLICY_CONFIG, 0);
+	}
+
 	if (icpu->disable_promotion_to_c1e)	/* each-cpu is redundant */
 		on_each_cpu(c1e_promotion_disable, NULL, 1);