i.MX8M DeviceTree UART2 DMA support

[RBdf]

The DeviceTree file for the i.MX8M (imx8mm.dtsi) does contain pre-configuration for all 4 UARTs but DMA support is enabled for UARTs 1, 3, and 4 only - not for UART2. Is there any reason for that or are the lines just missing?

[BiyongSUN · Accepted solution]

Because it is debug uart port, need atom operation. 

If you check all the device tree, you will find the debug uart port. they all have no dma.

and they should  not have dma. 

If you check the following link, you will see change to the uart4 from uart2.

uart4 also need to remove dma. 

How to Change i.MX8MM evk Linux Debug UART - NXP Community

i.MX8MM_evk_debug_uart4_rel_imx_5.4.70_2.3.0.patch

&uart2 {
+ dmas = <&sdma1 24 4 0>, <&sdma1 25 4 0>;
+ dma-names = "rx", "tx";
+};
+
+&uart4 {
+ /delete-property/ dmas;
+ /delete-property/ dmas-names;
u-boot,dm-spl;
};

[igorpadykov]

Hi Rainer

uart2 has dma capability as described in sect.2.1.4 DMA memory maps

i.MX 8M Mini Applications Processor Reference Manual

however dma is not used for uart console ports.

Best regards
igor