powerpc/powernv: Enable Offline CPUs to enter deep idle states

The secondary threads should enter deep idle states so as to gain maximum
powersavings when the entire core is offline. To do so the offline path
must be made aware of the available deepest idle state. Hence probe the
device tree for the possible idle states in powernv core code and
expose the deepest idle state through flags.

Since the  device tree is probed by the cpuidle driver as well, move
the parameters required to discover the idle states into an appropriate
common place to both the driver and the powernv core code.

Another point is that fastsleep idle state may require workarounds in
the kernel to function properly. This workaround is introduced in the
subsequent patches. However neither the cpuidle driver or the hotplug
path need be bothered about this workaround.

They will be taken care of by the core powernv code.

Originally-by: Srivatsa S. Bhat <srivatsa@mit.edu>
Signed-off-by: Preeti U. Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com>
Reviewed-by: Paul Mackerras <paulus@samba.org>

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: linux-pm@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/setup.c

@@ -288,6 +288,55 @@ static void __init pnv_setup_machdep_rtas(void)
 }
 #endif /* CONFIG_PPC_POWERNV_RTAS */
 
+static u32 supported_cpuidle_states;
+
+u32 pnv_get_supported_cpuidle_states(void)
+{
+	return supported_cpuidle_states;
+}
+
+static int __init pnv_init_idle_states(void)
+{
+	struct device_node *power_mgt;
+	int dt_idle_states;
+	const __be32 *idle_state_flags;
+	u32 len_flags, flags;
+	int i;
+
+	supported_cpuidle_states = 0;
+
+	if (cpuidle_disable != IDLE_NO_OVERRIDE)
+		return 0;
+
+	if (!firmware_has_feature(FW_FEATURE_OPALv3))
+		return 0;
+
+	power_mgt = of_find_node_by_path("/ibm,opal/power-mgt");
+	if (!power_mgt) {
+		pr_warn("opal: PowerMgmt Node not found\n");
+		return 0;
+	}
+
+	idle_state_flags = of_get_property(power_mgt,
+			"ibm,cpu-idle-state-flags", &len_flags);
+	if (!idle_state_flags) {
+		pr_warn("DT-PowerMgmt: missing ibm,cpu-idle-state-flags\n");
+		return 0;
+	}
+
+	dt_idle_states = len_flags / sizeof(u32);
+
+	for (i = 0; i < dt_idle_states; i++) {
+		flags = be32_to_cpu(idle_state_flags[i]);
+		supported_cpuidle_states |= flags;
+	}
+
+	return 0;
+}
+
+subsys_initcall(pnv_init_idle_states);
+
+
 static int __init pnv_probe(void)
 {
 	unsigned long root = of_get_flat_dt_root();