ARM: dts: bcm2711: Allow 40-bit DMA for SPI

Add the spi_dma4 DT parameter to enable use of the 40-bit DMA channels
to drive SPI. Note that there are only 3-4 40-bit channels available,
and using this parameter claims 2 of them.

Usage: dtparam=spi_dma4

Signed-off-by: Phil Elwell <[email protected]>

Author: pelwell

arch/arm/boot/dts/bcm2711-rpi-4-b.dts

@@ -365,5 +365,7 @@
 		eth_led1 = <&phy1>,"led-modes:4";
 
 		sd_poll_once = <&emmc2>, "non-removable?";
+		spi_dma4 = <&spi0>, "dmas:0=", <&dma40>,
+			   <&spi0>, "dmas:8=", <&dma40>;
 	};
 };

arch/arm/boot/dts/overlays/README

@@ -159,6 +159,10 @@ Params:
         spi                     Set to "on" to enable the spi interfaces
                                 (default "off")
 
+        spi_dma4                Use to enable 40-bit DMA on spi interfaces
+                                (the assigned value doesn't matter)
+                                (2711 only)
+
         random                  Set to "on" to enable the hardware random
                                 number generator (default "on")