dts: bcm2712-rpi: Add uart0_nodma

uart0_nodma enables UART0 (as found on GPIOs 14 & 15, pins 8 & 10 on the
40 pin header) but without DMA. This may be useful to free up some DMA
channels, and can help in cases where DMA may not be working.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>

Author: pelwell

arch/arm/boot/dts/overlays/README

@@ -454,12 +454,16 @@ Params:
                                 and entering the low power state (default 600).
                                 Requires EEE to be enabled - see "eee".
 
-        uart0                   Set to "off" to disable uart0 (default "on")
+        uart0                   Set to "on" to enable and "off" to disable uart0
+                                (default "off" on 2712, otherwise "on")
 
         uart0_console           Move the kernel boot console to UART0 on pins
                                 6, 8 and 10 of the 40-way header (2712 only,
                                 default "off")
 
+        uart0_nodma             Enable uart0 without DMA (2712 only, default
+                                "off")
+
         uart1                   Set to "on" or "off" to enable or disable uart1
                                 (default varies)
 

arch/arm64/boot/dts/broadcom/bcm2712-rpi.dtsi

@@ -220,6 +220,7 @@ pio: &rp1_pio {
 		suspend = <&pwr_key>, "linux,code:0=205";
 		uart0 = <&uart0>, "status";
 		uart0_console = <&uart0>,"status", <&aliases>, "console=",&uart0;
+		uart0_nodma = <&uart0>,"status", <&uart0>,"dma-names?=0";
 		wifiaddr = <&wifi>, "local-mac-address[";
 
 		cam0_reg = <&cam0_reg>,"status";