问题背景
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。
分析思路
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
1.需要在uboot中配置以下编译选项
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
2. 内核配置
内核配置文件路径：packages/linux/linux/arch/arm64/configs/ok1028_defconfig
3.设备树绑定
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 = <GIC_SPI 232 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&sysclk>;
clock-names = "ipg";
fsl,lpuart32;
status = "okay";
};
lpuart1: serial@2270000 {
compatible = "fsl,ls1028a-lpuart";
reg = <0x0 0x2270000 0x0 0x1000>;
interrupts = <GIC_SPI 233 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&clockgen 4 1>;
clock-names = "ipg";
fsl,lpuart32;
status = "okay";
};
4.验证
全编译烧写到板子上，可以看到生成了lpuart1、lpuart2的设备节点
其他
添加的设备节点分析
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";
};
