[RK3399] 调试串口ttyS2改为普通串口

CPU：RK3399

系统：Android 7.1

串口需求量大时，会选择使用 spi 转串口，但是数据量大或者波特率较高时，传输会丢包。

调试串口 ttyS2 也可以让出来，供上层使用，下面是将 ttyS2 改为普通串口。

1、在配置文件中关闭 FIQ

使用 rockchip_defconfig 文件，就在此文件中修改

diff --git a/kernel/arch/arm64/configs/rockchip_defconfig b/kernel/arch/arm64/configs/rockchip_defconfig
index dad111e..6d974cb
--- a/kernel/arch/arm64/configs/rockchip_defconfig
+++ b/kernel/arch/arm64/configs/rockchip_defconfig
@@ -, +, @@ CONFIG_SW_SYNC=y
 CONFIG_SW_SYNC_USER=y
 CONFIG_ION=y
 CONFIG_ION_ROCKCHIP=y
-CONFIG_FIQ_DEBUGGER=y
-CONFIG_FIQ_DEBUGGER_NO_SLEEP=y
-CONFIG_FIQ_DEBUGGER_CONSOLE=y
-CONFIG_FIQ_DEBUGGER_CONSOLE_DEFAULT_ENABLE=y
-CONFIG_FIQ_DEBUGGER_TRUST_ZONE=y
+# CONFIG_FIQ_DEBUGGER is not set
 CONFIG_RK_CONSOLE_THREAD=y
 CONFIG_POWERVR_ROGUE_N=y
 CONFIG_COMMON_CLK_RK808=y

如果不用 rockchip_defconfig 文件，就直接修改 kernel 目录下的 .config 文件（与 rockchip_defconfig 相同），或者在 make menuconfig 中关闭

Device Drivers  --->

　　[*] Staging drivers  --->

　　　　Android  --->

　　　　　　[ ] FIQ Mode Serial Debugger

2、dts 文件中关闭调试

diff --git a/kernel/arch/arm64/boot/dts/rockchip/rk3399-android.dtsi b/kernel/arch/arm64/boot/dts/rockchip/rk3399-android.dtsi
index cdd464d..2de1631
--- a/kernel/arch/arm64/boot/dts/rockchip/rk3399-android.dtsi
+++ b/kernel/arch/arm64/boot/dts/rockchip/rk3399-android.dtsi
@@ -, +, @@
        compatible = "rockchip,android", "rockchip,rk3399";

        chosen {
-               bootargs = "earlycon=uart8250,mmio32,0xff1a0000 swiotlb=1 coherent_pool=1m";
+//             bootargs = "earlycon=uart8250,mmio32,0xff1a0000 swiotlb=1 coherent_pool=1m";
+               bootargs = "";
        };

        cpuinfo {
@@ -, +, @@
        fiq_debugger: fiq-debugger {
                compatible = "rockchip,fiq-debugger";
                rockchip,serial-id = <>;
                rockchip,wake-irq = <>;
                rockchip,irq-mode-enable = <>;  /* If enable uart uses irq instead of fiq */
                rockchip,baudrate = <>;  /* Only 115200 and 1500000 */
                pinctrl-names = "default";
                pinctrl- = <&uart2c_xfer>;
                interrupts = <GIC_SPI  IRQ_TYPE_LEVEL_HIGH >;
+                status = "disabled";
        };

3、打开 ttyS2 串口，这样上层才能识别到 ttyS2

diff --git a/kernel/arch/arm64/boot/dts/rockchip/rk3399-mid--android.dts b/kernel/arch/arm64/boot/dts/rockchip/rk3399-mid--android.dts
old mode
new mode
index 60460be..57749a4
--- a/kernel/arch/arm64/boot/dts/rockchip/rk3399-mid--android.dts
+++ b/kernel/arch/arm64/boot/dts/rockchip/rk3399-mid--android.dts
@@ -, +, @@
        status = "okay";
 };

+&uart2 {
+       pinctrl-names = "default";
+       pinctrl- = <&uart2c_xfer>;
+       status = "okay";
+};
+
 &usb_host0_ehci {
        status = "okay";
 };

4、修改 ttyS2 权限

diff --git a/device/rockchip/common/ueventd.rockchip.rc b/device/rockchip/common/ueventd.rockchip.rc
index 8d5d28d..
--- a/device/rockchip/common/ueventd.rockchip.rc
+++ b/device/rockchip/common/ueventd.rockchip.rc
@@ -, +, @@
#/dev/ttyS2  bluetooth net_bt_stack
/dev/rtk_btusb  bluetooth net_bt_stack

+/dev/ttyS2  system system

此时开机进入 kernel 后，ttyS2 不会再输出打印信息，但是 u-boot 中的打印信息还在，但已经不影响上层使用。