overlays: Add "always-on" parameter to imx477 and imx296

Leave the camera's power supplies up, to prevent the camera
clamping its 1.8V digital I/Os to ground. This may be useful
when synchronizing multiple camera systems using XVS or XTRIG.

Signed-off-by: Nick Hollinghurst <nick.hollinghurst@raspberrypi.com>

Author: njhollinghurst

arch/arm/boot/dts/overlays/README

@@ -2520,6 +2520,8 @@ Params: rotation                Mounting rotation of the camera sensor (0 or
         clock-frequency         Sets the clock frequency to match that used on
                                 the board, which should be one of 54000000
                                 (the default), 37125000 or 74250000.
+        always-on               Leave the regulator powered up, to stop the
+                                camera clamping I/Os such as XTRIG to 0V.
 
 
 Name:   imx327
@@ -2558,6 +2560,8 @@ Params: rotation                Mounting rotation of the camera sensor (0 or
                                 configuring the sensor (default on)
         cam0                    Adopt the default configuration for CAM0 on a
                                 Compute Module (CSI0, i2c_vc, and cam0_reg).
+        always-on               Leave the regulator powered up, to stop the
+                                camera clamping I/Os such as XVS to 0V.
 
 
 Name:   imx462
@@ -2596,6 +2600,8 @@ Params: rotation                Mounting rotation of the camera sensor (0 or
                                 configuring the sensor (default on)
         cam0                    Adopt the default configuration for CAM0 on a
                                 Compute Module (CSI0, i2c_vc, and cam0_reg).
+        always-on               Leave the regulator powered up, to stop the
+                                camera clamping I/Os such as XVS to 0V.
 
 
 Name:   imx519

arch/arm/boot/dts/overlays/imx296-overlay.dts

@@ -37,6 +37,13 @@
 		};
 	};
 
+	reg_alwayson_frag: fragment@99 {
+		target = <&cam1_reg>;
+		__dormant__ {
+			regulator-always-on;
+		};
+	};
+
 	i2c_frag: fragment@100 {
 		target = <&i2c_csi_dsi>;
 		__overlay__ {
@@ -98,8 +105,10 @@
 		       <&csi_frag>, "target:0=",<&csi0>,
 		       <&clk_frag>, "target:0=",<&cam0_clk>,
 		       <&reg_frag>, "target:0=",<&cam0_reg>,
+		       <&reg_alwayson_frag>, "target:0=",<&cam0_reg>,
 		       <&imx296>, "clocks:0=",<&cam0_clk>,
 		       <&imx296>, "avdd-supply:0=",<&cam0_reg>;
 		clock-frequency = <&clk_over>, "clock-frequency:0";
+		always-on = <0>, "+99";
 	};
 };

arch/arm/boot/dts/overlays/imx477_378-overlay.dtsi

@@ -33,6 +33,13 @@
 		};
 	};
 
+	reg_alwayson_frag: fragment@99 {
+		target = <&cam1_reg>;
+		__dormant__ {
+			regulator-always-on;
+		};
+	};
+
 	i2c_frag: fragment@100 {
 		target = <&i2c_csi_dsi>;
 		__overlay__ {
@@ -69,8 +76,10 @@
 		       <&csi_frag>, "target:0=",<&csi0>,
 		       <&clk_frag>, "target:0=",<&cam0_clk>,
 		       <&reg_frag>, "target:0=",<&cam0_reg>,
+		       <&reg_alwayson_frag>, "target:0=",<&cam0_reg>,
 		       <&cam_node>, "clocks:0=",<&cam0_clk>,
 		       <&cam_node>, "VANA-supply:0=",<&cam0_reg>;
+		always-on = <0>, "+99";
 	};
 };