Ls1028 LPUART配置

LS1028原生支持两路uart和六路lpuart，OK1028A-C底板上只用了两路uart，客户在实际的应用中发现串口太少，就想使用lpuart串口。

在原厂资料的《LSDKUG_Rev20.4.pdf》有关于LPUART的配置说明，参照里面的说明进行配置

配置文件路径packages/firmware/u-boot/configs/ls1028ardb_tfa_defconfig，添加：

CONFIG_LPUART=y
CONFIG_FSL_LPUART=y
CONFIG_LPUART_32B_REG=y

内核配置文件路径：packages/linux/linux/arch/arm64/configs/ok1028_defconfig

设备树dtsi路径：OK1028-linux-fs/packages/linux/linux/arch/arm64/boot/dts/freescale/fsl-ls1028a.dtsi
添加lpuart设备节点：

lpuart0: serial@2260000 {
                        compatible = "fsl,ls1028a-lpuart";
                        reg = <0x0 0x2260000 0x0 0x1000>;
                        interrupts = ;
                         clocks = <&sysclk>;
                        clock-names = "ipg";
                        fsl,lpuart32;
                        status = "okay";
                };
  lpuart1: serial@2270000 {
                         compatible = "fsl,ls1028a-lpuart";
                         reg = <0x0 0x2270000 0x0 0x1000>;
                         interrupts = ;
                         clocks = <&clockgen 4 1>;
                         clock-names = "ipg";
                         fsl,lpuart32;
                         status = "okay";
                };

全编译烧写到板子上，可以看到生成了lpuart1、lpuart2的设备节点

分析：
1)reg ：
LPUART1 base address: 226_0000h
LPUART2 base address: 227_0000h

2)Interrupts中断：（参考链接：http://www.lujun.org.cn/?p=3834）

1028使用的SPI：（shared peripheral interrupt），共享外设中断，该中断来源于外设，但是该中断可以对所有的core有效。
在CPU手册里面查看LPUART的中断号为264，但设备树里面是从0开始的，故要减32，所以为232

3) clocks
LPUART参考时钟，LPUART1时钟参考源为系统参考时钟，根据clockgen参考时钟的定义

设备树里面用的参考时钟

clockgen的定义：/Documentation/devicetree/binding/clock/qoriq-clock.txt
可以看到时钟参考源的选择

lpuart设备树节点定义:/Documentation/devicetree/binding/serial/fsl-lpuart.txt

Required properties:
- compatible :
  - "fsl,vf610-lpuart" for lpuart compatible with the one integrated
    on Vybrid vf610 SoC with 8-bit register organization
- reg : Address and length of the register set for the device
- interrupts : Should contain uart interrupt
- clocks : phandle + clock specifier pairs, one for each entry in clock-names
- clock-names : For vf610/ls1021a/imx7ulp, "ipg" clock is for uart bus/baud
  clock. For imx8qxp lpuart, "ipg" clock is bus clock that is used to access
  lpuart controller registers, it also requires "baud" clock for module to
  receive/transmit data.
Optional properties:
- dmas: A list of two dma specifiers, one for each entry in dma-names.
- dma-names: should contain "tx" and "rx".
- rs485-rts-delay, rs485-rts-active-low, rs485-rx-during-tx,
  linux,rs485-enabled-at-boot-time: see rs485.txt

Note: Optional properties for DMA support. Write them both or both not.

Example:

uart0: serial@40027000 {
                compatible = "fsl,vf610-lpuart";
                reg = <0x40027000 0x1000>;
                interrupts = <0 61 0x00>;
                clocks = <&clks VF610_CLK_UART0>;
                clock-names = "ipg";
                dmas = <&edma0 0 2>,
                        <&edma0 0 3>;
                dma-names = "rx","tx";
        };