PM / OPP: Add support for opp-suspend

With "operating-points-v2" bindings, it's possible to specify the OPP to
which the device must be switched, before suspending.

This patch adds support for getting that information.
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Reviewed-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/opp.c

@@ -133,6 +133,7 @@ struct device_opp {
 	struct device_node *np;
 	unsigned long clock_latency_ns_max;
 	bool shared_opp;
+	struct dev_pm_opp *suspend_opp;
 };
 
 /*
@@ -923,6 +924,16 @@ static int _opp_add_static_v2(struct device *dev, struct device_node *np)
 	if (ret)
 		goto free_opp;
 
+	/* OPP to select on device suspend */
+	if (of_property_read_bool(np, "opp-suspend")) {
+		if (dev_opp->suspend_opp)
+			dev_warn(dev, "%s: Multiple suspend OPPs found (%lu %lu)\n",
+				 __func__, dev_opp->suspend_opp->rate,
+				 new_opp->rate);
+		else
+			dev_opp->suspend_opp = new_opp;
+	}
+
 	if (new_opp->clock_latency_ns > dev_opp->clock_latency_ns_max)
 		dev_opp->clock_latency_ns_max = new_opp->clock_latency_ns;