RZ/G2L串口簡介

瑞薩RZ/G2L的串口簡稱SCI，全稱Serial Communication Interface。

RZ/G2L有兩種串口，一種帶FIFO叫SCIFA，另一種不帶FIFO叫SCIg。

所以，RZ/G2L有5路SCIFA和2路SCIg總共7路的串口。

RZ/G2L串口驅動

包含驅動代碼和設備樹兩部分：

內核中的驅動文件sh-sci.c

該源碼文件路徑：drivers/tty/serial/sh-sci.c，該驅動代碼包含SCIFA和SCIg兩種型號的完整驅動代碼。

編譯內核的時候需進行以下配置

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egrep -rin "CONFIG_SERIAL_SH_SCI" .out/.config
2180:CONFIG_SERIAL_SH_SCI=y
2181:CONFIG_SERIAL_SH_SCI_NR_UARTS=18
2182:CONFIG_SERIAL_SH_SCI_CONSOLE=y
2183:CONFIG_SERIAL_SH_SCI_EARLYCON=y
2184:CONFIG_SERIAL_SH_SCI_DMA=y

該配置能夠確保sh-sci.c的驅動代碼能夠被編譯包含到Image中。

github上提供的內核源碼的defconfig中默認已包含SCI驅動代碼的編譯。

SCI串口的設備樹節點在r9a07g044.dtsi中定義，分別定義了scif0~4, sci0~1共7路。

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    scif0: serial@1004b800 {
      compatible = "renesas,scif-r9a07g044";
      reg = <0 0x1004b800 0 0x400>;
      interrupts = ,
             ,
             ,
             ,
             ,
             ;
      interrupt-names = "eri", "rxi", "txi",
            "bri", "dri", "tei";
      clocks = <&cpg CPG_MOD R9A07G044_SCIF0_CLK_PCK>;
      clock-names = "fck";
      dmas = <&dmac 0x4e79>, <&dmac 0x4e7a>;
      dma-names = "tx", "rx";
      power-domains = <&cpg>;
      resets = <&cpg R9A07G044_SCIF0_RST_SYSTEM_N>;
      status = "disabled";
    };


    scif1: serial@1004bc00 {
      compatible = "renesas,scif-r9a07g044";
      reg = <0 0x1004bc00 0 0x400>;
      interrupts = ,
             ,
             ,
             ,
             ,
             ;
      interrupt-names = "eri", "rxi", "txi",
            "bri", "dri", "tei";
      clocks = <&cpg CPG_MOD R9A07G044_SCIF1_CLK_PCK>;
      clock-names = "fck";
      dmas = <&dmac 0x4e7d>, <&dmac 0x4e7e>;
      dma-names = "tx", "rx";
      power-domains = <&cpg>;
      resets = <&cpg R9A07G044_SCIF1_RST_SYSTEM_N>;
      status = "disabled";
    };


    scif2: serial@1004c000 {
      compatible = "renesas,scif-r9a07g044";
      reg = <0 0x1004c000 0 0x400>;
      interrupts = ,
             ,
             ,
             ,
             ,
             ;
      interrupt-names = "eri", "rxi", "txi",
            "bri", "dri", "tei";
      clocks = <&cpg CPG_MOD R9A07G044_SCIF2_CLK_PCK>;
      clock-names = "fck";
      dmas = <&dmac 0x4e81>, <&dmac 0x4e82>;
      dma-names = "tx", "rx";
      power-domains = <&cpg>;
      resets = <&cpg R9A07G044_SCIF2_RST_SYSTEM_N>;
      status = "disabled";
    };


    scif3: serial@1004c400 {
      compatible = "renesas,scif-r9a07g044";
      reg = <0 0x1004c400 0 0x400>;
      interrupts = ,
             ,
             ,
             ,
             ,
             ;
      interrupt-names = "eri", "rxi", "txi",
            "bri", "dri", "tei";
      clocks = <&cpg CPG_MOD R9A07G044_SCIF3_CLK_PCK>;
      clock-names = "fck";
      dmas = <&dmac 0x4e85>, <&dmac 0x4e86>;
      dma-names = "tx", "rx";
      power-domains = <&cpg>;
      resets = <&cpg R9A07G044_SCIF3_RST_SYSTEM_N>;
      status = "disabled";
    };


    scif4: serial@1004c800 {
      compatible = "renesas,scif-r9a07g044";
      reg = <0 0x1004c800 0 0x400>;
      interrupts = ,
             ,
             ,
             ,
             ,
             ;
      interrupt-names = "eri", "rxi", "txi",
            "bri", "dri", "tei";
      clocks = <&cpg CPG_MOD R9A07G044_SCIF4_CLK_PCK>;
      clock-names = "fck";
      dmas = <&dmac 0x4e89>, <&dmac 0x4e8a>;
      dma-names = "tx", "rx";
      power-domains = <&cpg>;
      resets = <&cpg R9A07G044_SCIF4_RST_SYSTEM_N>;
      status = "disabled";
    };


    sci0: serial@1004d000 {
      compatible = "renesas,r9a07g044-sci", "renesas,rz-sci";
      reg = <0 0x1004d000 0 0x400>;
      interrupts = ,
             ,
             ,
             ;
      interrupt-names = "eri", "rxi", "txi", "tei";
      clocks = <&cpg CPG_MOD R9A07G044_SCI0_CLKP>;
      clock-names = "fck";
      power-domains = <&cpg>;
      resets = <&cpg R9A07G044_SCI0_RST>;
      status = "disabled";
    };


    sci1: serial@1004d400 {
      compatible = "renesas,r9a07g044-sci", "renesas,rz-sci";
      reg = <0 0x1004d400 0 0x400>;
      interrupts = ,
             ,
             ,
             ;
      interrupt-names = "eri", "rxi", "txi", "tei";
      clocks = <&cpg CPG_MOD R9A07G044_SCI1_CLKP>;
      clock-names = "fck";
      power-domains = <&cpg>;
      resets = <&cpg R9A07G044_SCI1_RST>;
      status = "disabled";
    };

設備樹文件路徑

arch/arm64/boot/dts/renesas/r9a07g044.dtsi

根據項目需要，使能需要使用的設備節點，如欲使用SCIFA2：

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&scif2 {
 pinctrl-0 = <&scif2_pins>;
 pinctrl-names = "default";
 uart-has-rtscts;
 status = "okay";
};

注意需通過scif2_pins正確處理IO口復用問題。如果不使用DMA需要將設備節點中的dmas和dma-names刪除。

編譯內核：

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export ARCH=arm64
export CROSS_COMPILE=aarch64-none-elf-
export PATH=$PATH:/opt/arm/gcc-arm-10.2-2020.11-x86_64-aarch64-none-elf/bin
make defconfig O=.out && make -j8 O=.out

使用當前編譯生成的內核Image和dtb

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.out/arch/arm64/boot/Image 
.out/arch/arm64/boot/dts/renesas/r9a07g044l2-smarc.dtb

啟動板子后就能在系統路徑下生成/dev/ttySC2節點。

Linux應用層使用RZ/G2L的串口SCI

RZ/G2L的串口設備節點在Linux應用層遵循POSIX標準，使用方法和PC端的Ubuntu系統并無差別。

RZ/G2L除了支持市面上常用的串口波特率如9600/115200/921600等，實際上除POSIX系統定義的波特率都支持外，RZ/G2L能夠支持的最大串口波特率是12.5Mbps，下一篇我們將介紹如何在內核驅動代碼中實現RZ/G2L的最大波特率12.5Mbps。

審核編輯：湯梓紅