[PATCH v2 3/4] arm64: dts: imx8mp-kontron: Fix boot order for PMIC and RTC

[Frieder Schrempf <frieder@fris.de>]

From: Annette Kobou <annette.kobou@kontron.de>

The PMIC provides a level-shifter for the I2C lines to the RTC.
As the level shifter needs to be enabled before the RTC can be
accessed, we need to make sure that the PMIC driver is probed
first.

As the PMIC also provides the supply voltage for the RTC through
the 3.3V regulator, we can simply express this in the DT to
create the required dependency.

This fixes sporadic boot hangs that occurred when the RTC was
accessed before the level-shifter was enabled.

Fixes: 946ab10e3f40f ("arm64: dts: Add support for Kontron OSM-S i.MX8MP SoM and BL carrier board")
Signed-off-by: Annette Kobou <annette.kobou@kontron.de>
Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
---
 arch/arm64/boot/dts/freescale/imx8mp-kontron-osm-s.dtsi | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/arm64/boot/dts/freescale/imx8mp-kontron-osm-s.dtsi b/arch/arm64/boot/dts/freescale/imx8mp-kontron-osm-s.dtsi
index b97bfeb1c30f8..bc1a261bb000e 100644
--- a/arch/arm64/boot/dts/freescale/imx8mp-kontron-osm-s.dtsi
+++ b/arch/arm64/boot/dts/freescale/imx8mp-kontron-osm-s.dtsi
@@ -330,6 +330,12 @@ rv3028: rtc@52 {
 		pinctrl-names = "default";
 		pinctrl-0 = <&pinctrl_rtc>;
 		interrupts-extended = <&gpio3 24 IRQ_TYPE_LEVEL_LOW>;
+		/*
+		 * While specifying the vdd-supply is normally not strictly necessary,
+		 * here it also makes sure that the PMIC driver enables the level-
+		 * shifter for the RTC before the RTC is probed.
+		 */
+		vdd-supply = <&reg_vdd_3v3>;
 	};
 };
 
-- 
2.52.0