soc/tegra: Enable runtime PM during OPP state-syncing

GENPD core now can set up domain's performance state properly while device
is RPM-suspended. Runtime PM of a device must be enabled during setup
because GENPD checks whether device is suspended and check doesn't work
while RPM is disabled. Instead of replicating the boilerplate RPM-enable
code around OPP helper for each driver, let's make OPP helper to take care
of enabling it.

Reviewed-by: Ulf Hansson <[e-mail]>
Signed-off-by: Dmitry Osipenko <[e-mail]>
Signed-off-by: Thierry Reding <[e-mail]>

drivers/soc/tegra/common.c

···
 #include <linux/export.h>
 #include <linux/of.h>
 #include <linux/pm_opp.h>
+#include <linux/pm_runtime.h>
 
 #include <soc/tegra/common.h>
 #include <soc/tegra/fuse.h>
···
 {
 	unsigned long rate;
 	struct clk *clk;
+	bool rpm_enabled;
 	int err;
 
 	clk = devm_clk_get(dev, NULL);
···
 		return -EINVAL;
 	}
 
+	/*
+	 * Runtime PM of the device must be enabled in order to set up
+	 * GENPD's performance properly because GENPD core checks whether
+	 * device is suspended and this check doesn't work while RPM is
+	 * disabled. This makes sure the OPP vote below gets cached in
+	 * GENPD for the device. Instead, the vote is done the next time
+	 * the device gets runtime resumed.
+	 */
+	rpm_enabled = pm_runtime_enabled(dev);
+	if (!rpm_enabled)
+		pm_runtime_enable(dev);
+
+	/* should never happen in practice */
+	if (!pm_runtime_enabled(dev)) {
+		dev_WARN(dev, "failed to enable runtime PM\n");
+		pm_runtime_disable(dev);
+		return -EINVAL;
+	}
+
 	/* first dummy rate-setting initializes voltage vote */
 	err = dev_pm_opp_set_rate(dev, rate);
+
+	if (!rpm_enabled)
+		pm_runtime_disable(dev);
+
 	if (err) {
 		dev_err(dev, "failed to initialize OPP clock: %d\n", err);
 		return err;