mwait-idle: support Bay Trail

Bay Trail (BYT) is a family of Silvermont-core Atom Processor SOCs,
including the Intel Atom Processor Z36xxx and Z37xxx Series.

Although it shares the Silvermont core with Avoton,
BYT is optimized for mobile, and thus it supports
different power saving CPU idle states.

Note that not all versions of Bay Trail HW support all
of the states listed in the driver.

Signed-off-by: Len Brown <len.brown@xxxxxxxxx>
Tested-by: Aubrey Li <aubrey.li@xxxxxxxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/cpu/mwait-idle.c
+++ b/xen/arch/x86/cpu/mwait-idle.c
@@ -187,6 +187,46 @@ static const struct cpuidle_state snb_cs
 	{}
 };
 
+static const struct cpuidle_state byt_cstates[] = {
+	{
+		.name = "C1-BYT",
+		.flags = MWAIT2flg(0x00),
+		.exit_latency = 1,
+		.target_residency = 1,
+	},
+	{
+		.name = "C1E-BYT",
+		.flags = MWAIT2flg(0x01),
+		.exit_latency = 15,
+		.target_residency = 30,
+	},
+	{
+		.name = "C6N-BYT",
+		.flags = MWAIT2flg(0x58) | CPUIDLE_FLAG_TLB_FLUSHED,
+		.exit_latency = 40,
+		.target_residency = 275,
+	},
+	{
+		.name = "C6S-BYT",
+		.flags = MWAIT2flg(0x52) | CPUIDLE_FLAG_TLB_FLUSHED,
+		.exit_latency = 140,
+		.target_residency = 560,
+	},
+	{
+		.name = "C7-BYT",
+		.flags = MWAIT2flg(0x60) | CPUIDLE_FLAG_TLB_FLUSHED,
+		.exit_latency = 1200,
+		.target_residency = 1500,
+	},
+	{
+		.name = "C7S-BYT",
+		.flags = MWAIT2flg(0x64) | CPUIDLE_FLAG_TLB_FLUSHED,
+		.exit_latency = 10000,
+		.target_residency = 20000,
+	},
+	{}
+};
+
 static const struct cpuidle_state ivb_cstates[] = {
 	{
 		.name = "C1-IVB",
@@ -444,6 +484,11 @@ static const struct idle_cpu idle_cpu_sn
 	.disable_promotion_to_c1e = 1,
 };
 
+static const struct idle_cpu idle_cpu_byt = {
+	.state_table = byt_cstates,
+	.disable_promotion_to_c1e = 1,
+};
+
 static const struct idle_cpu idle_cpu_ivb = {
 	.state_table = ivb_cstates,
 	.disable_promotion_to_c1e = 1,
@@ -476,6 +521,7 @@ static struct intel_idle_id {
 	ICPU(0x26, lincroft),
 	ICPU(0x2a, snb),
 	ICPU(0x2d, snb),
+	ICPU(0x37, byt),
 	ICPU(0x3a, ivb),
 	ICPU(0x3e, ivb),
 	ICPU(0x3c, hsw),