intel_pstate: Knights Landing support

 1. Add Knights Landing (KNL) CPUID to the list of CPUIDs supported by
    the intel_pstate driver.

 2. Add a new cpu_default structure for KNL since KNL has a slightly
    different mechanism to get turbo pstates from MSRs.

Signed-off-by: Dasaratharaman Chandramouli <dasaratharaman.chandramouli@intel.com>
Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
[ rjw: Subject and changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/intel_pstate.c

@@ -614,6 +614,19 @@ static void core_set_pstate(struct cpudata *cpudata, int pstate)
 	wrmsrl_on_cpu(cpudata->cpu, MSR_IA32_PERF_CTL, val);
 }
 
+static int knl_get_turbo_pstate(void)
+{
+	u64 value;
+	int nont, ret;
+
+	rdmsrl(MSR_NHM_TURBO_RATIO_LIMIT, value);
+	nont = core_get_max_pstate();
+	ret = (((value) >> 8) & 0xFF);
+	if (ret <= nont)
+		ret = nont;
+	return ret;
+}
+
 static struct cpu_defaults core_params = {
 	.pid_policy = {
 		.sample_rate_ms = 10,
@@ -651,6 +664,23 @@ static struct cpu_defaults byt_params = {
 	},
 };
 
+static struct cpu_defaults knl_params = {
+	.pid_policy = {
+		.sample_rate_ms = 10,
+		.deadband = 0,
+		.setpoint = 97,
+		.p_gain_pct = 20,
+		.d_gain_pct = 0,
+		.i_gain_pct = 0,
+	},
+	.funcs = {
+		.get_max = core_get_max_pstate,
+		.get_min = core_get_min_pstate,
+		.get_turbo = knl_get_turbo_pstate,
+		.set = core_set_pstate,
+	},
+};
+
 static void intel_pstate_get_min_max(struct cpudata *cpu, int *min, int *max)
 {
 	int max_perf = cpu->pstate.turbo_pstate;
@@ -865,6 +895,7 @@ static const struct x86_cpu_id intel_pstate_cpu_ids[] = {
 	ICPU(0x4e, core_params),
 	ICPU(0x4f, core_params),
 	ICPU(0x56, core_params),
+	ICPU(0x57, knl_params),
 	{}
 };
 MODULE_DEVICE_TABLE(x86cpu, intel_pstate_cpu_ids);