PM / devfreq: rk3399_dmc: Block PMU during transitions

See the previous patch ("soc: rockchip: power-domain: Manage resource
conflicts with firmware") for a thorough explanation of the conflicts.
While ARM Trusted Firmware may be modifying memory controller and
power-domain states, we need to block the kernel's power-domain driver.

If the power-domain driver is disabled, there is no resource conflict
and this becomes a no-op.
Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

drivers/devfreq/rk3399_dmc.c

@@ -21,6 +21,7 @@
 #include <linux/rwsem.h>
 #include <linux/suspend.h>
 
+#include <soc/rockchip/pm_domains.h>
 #include <soc/rockchip/rk3399_grf.h>
 #include <soc/rockchip/rockchip_sip.h>
 
@@ -93,6 +94,16 @@ static int rk3399_dmcfreq_target(struct device *dev, unsigned long *freq,
 
 	mutex_lock(&dmcfreq->lock);
 
+	/*
+	 * Ensure power-domain transitions don't interfere with ARM Trusted
+	 * Firmware power-domain idling.
+	 */
+	err = rockchip_pmu_block();
+	if (err) {
+		dev_err(dev, "Failed to block PMU: %d\n", err);
+		goto out_unlock;
+	}
+
 	/*
 	 * Some idle parameters may be based on the DDR controller clock, which
 	 * is half of the DDR frequency.
@@ -198,6 +209,8 @@ static int rk3399_dmcfreq_target(struct device *dev, unsigned long *freq,
 	dmcfreq->volt = target_volt;
 
 out:
+	rockchip_pmu_unblock();
+out_unlock:
 	mutex_unlock(&dmcfreq->lock);
 	return err;
 }