opensbi串口驱动详解

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【资源中心】可验证AI开启EDA新时代 【2024 Arm Tech Symposia 报名开启】与Arm，重塑未来

一. 前言

本文分享OpenSBI串口驱动相关的实现,并实践添加自己的串口驱动。

整个框架如下

二. 串口驱动相关Kconfig与Makefile

2.1 Kconfig

要了解串口驱动的相关结构，最好的方式是从Kconfig和Makefile入手，看到底编译了哪些文件，结构是怎么样的。https://mp.weixin.qq.com/s/941A4li9L6kq1QB-fuyuVA opensbi单独构建与GDB仿真调试一文中介绍了Kconfig的结构。这里重点关注串口驱动相关的。

输入如下命令进入配置界面:

make PLATFORM=generic menuconfig

如下路径

Utils and Drivers Support --->

Serial Device Support--->

对应的文件就是lib/utils/serial/Kconfig

该Kconfig下，首先有个总的配置FDT_SERIAL,该配置选中，下面才会有各个driver选择。

FDT_SERIAL依赖于FDT配置。

而FDT配置是在platform/generic/Kconfig中，选中平台时自动选中的(make PLATFORM=generic menuconfig时自动选择的是platform/generic/Kconfig)。

Platform options --->

选中某个driver配置时，自动会select对应的串口底层实现

比如选中config FDT_SERIAL_CADENCE时自动选择select SERIAL_CADENCE。

2.2. Makefile

lib/utils/serial/objects.mk中就会根据上述Kconfig配置，是否添加对应的c文件进行编译。

libsbiutils-objs-$(CONFIG_FDT_SERIAL) += serial/fdt_serial.o

libsbiutils-objs-$(CONFIG_FDT_SERIAL) += serial/fdt_serial_drivers.carray.o

fdt_serial.c始终会编译

fdt_serial_drivers.carray.c是脚本自动生成的，后面介绍

如下驱动代码按照配置添加

carray-fdt_serial_drivers-$(CONFIG_FDT_SERIAL_CADENCE) += fdt_serial_cadence

libsbiutils-objs-$(CONFIG_FDT_SERIAL_CADENCE) += serial/fdt_serial_cadence.o

......

如下再根据配置添加串口底层实现文件

libsbiutils-objs-$(CONFIG_SERIAL_CADENCE) += serial/cadence-uart.o

......

上面提到的build/platform/generic/lib/utils/serial/fdt_serial_drivers.carray.c

在Makefile中如下实现

$(platform_build_dir)/%.carray.c: $(platform_src_dir)/%.carray

$(call compile_carray,$@,$<)

实现如下

compile_carray = $(CMD_PREFIX)mkdir -p `dirname $(1)`; \

echo " CARRAY $(subst $(build_dir)/,,$(1))"; \

$(eval CARRAY_VAR_LIST := $(carray-$(subst .carray.c,,$(shell basename $(1)))-y)) \

$(src_dir)/scripts/carray.sh -i $(2) -l "$(CARRAY_VAR_LIST)" > $(1)

即调用的脚本

scripts/carray.sh

根据

lib/utils/serial/fdt_serial_drivers.carray

HEADER: sbi_utils/serial/fdt_serial.h //头文件

TYPE: struct fdt_serial //数组类型

NAME: fdt_serial_drivers //指定数组结构名字，可以通过该全局变量索引指定的驱动

生成

build/platform/generic/lib/utils/serial/fdt_serial_drivers.carray.c

实际就是生成了全局数组 fdt_serial_drivers ，这个数组的成员即各个串口驱动的实现

// Generated with carray.sh from fdt_serial_drivers.carray#include 
extern struct fdt_serial fdt_serial_cadence;extern struct fdt_serial fdt_serial_gaisler;extern struct fdt_serial fdt_serial_htif;extern struct fdt_serial fdt_serial_renesas_scif;extern struct fdt_serial fdt_serial_shakti;extern struct fdt_serial fdt_serial_sifive;extern struct fdt_serial fdt_serial_litex;extern struct fdt_serial fdt_serial_uart8250;extern struct fdt_serial fdt_serial_xlnx_uartlite;
struct fdt_serial *fdt_serial_drivers[] = {    &fdt_serial_cadence,    &fdt_serial_gaisler,    &fdt_serial_htif,    &fdt_serial_renesas_scif,    &fdt_serial_shakti,    &fdt_serial_sifive,    &fdt_serial_litex,    &fdt_serial_uart8250,    &fdt_serial_xlnx_uartlite,};
unsigned long fdt_serial_drivers_size = sizeof(fdt_serial_drivers) / sizeof(struct fdt_serial *);

2.3 设备树

串口驱动上面可以选择同时支持多个，根据设备树来匹配具体是哪一个

sudo apt-get install device-tree-compiler

获取c-sky/buildroot的设备树。

dump设备树，注意逗号

./host/csky-qemu/bin/qemu-system-riscv64 -M virt,dumpdtb=dump.dtb

反编译

dtc -o dump.dts -O dts -I dtb dump.dtb

将dtb文件放置于platform/generic目录下

make PLATFORM=generic FW_TEXT_START=0x80000000 FW_FDT_PATH=/home/qinyunti/opensbi/platform/generic/dump.dtb

Dts串口相关内容如下，这是qemu的串口，根据实际平台修改。

chosen和uart两个节点必须要有。

/dts-v1/;
/ {  #address-cells = <0x02>;  #size-cells = <0x02>;  compatible = "riscv-virtio";  model = "riscv-virtio,qemu";
  chosen {    bootargs = [00];    stdout-path = "/uart@10000000";  };
  uart@10000000 {    interrupts = <0x0a>;    interrupt-parent = <0x03>;    clock-frequency = <1000000>;    current-speed = <115200>;    reg-shift = <0>;    reg-io-width = <1>;    reg-offset = <0>;    reg = <0x00 0x10000000 0x00 0x100>;    compatible = "xxx,xxx-uart";  };......

lib/utils/serial/fdt_serial.c中

fdt_serial_init中

会匹配设备树的串口节点的compatible和驱动中的serial_xxx_match中的compatible，

一致则调用该驱动的实现。

三. 添加自定义驱动

以下以添加自定义驱动为例分享整个过程

3.1. 添加源码

lib/utils/serial/下添加fdt_serial_xxx.c和xxx_uart.c

前者实现

struct fdt_serial fdt_serial_xxx = {

.match_table = serial_xxx_match,

.init = serial_xxx_init

};

后者实现

int xxx_uart_init(unsigned long base, u32 in_freq, u32 baudrate)

并调用sbi_console_set_device注册标准输入输出接口。

驱动代码以qemu的为例，根据实际修改

lib/utils/serial/xxx-uart.c内容如下

/* * SPDX-License-Identifier: BSD-2-Clause * * Copyright (c) 2019 . * * Authors: *    */
#include #include #include #include #include 
/* clang-format off */
#define UART_RBR_OFFSET     0   /* In:  Recieve Buffer Register */#define UART_THR_OFFSET     0   /* Out: Transmitter Holding Register */#define UART_DLL_OFFSET     0   /* Out: Divisor Latch Low */#define UART_IER_OFFSET     1   /* I/O: Interrupt Enable Register */#define UART_DLM_OFFSET     1   /* Out: Divisor Latch High */#define UART_FCR_OFFSET     2   /* Out: FIFO Control Register */#define UART_IIR_OFFSET     2   /* I/O: Interrupt Identification Register */#define UART_LCR_OFFSET     3   /* Out: Line Control Register */#define UART_MCR_OFFSET     4   /* Out: Modem Control Register */#define UART_LSR_OFFSET     5   /* In:  Line Status Register */#define UART_MSR_OFFSET     6   /* In:  Modem Status Register */#define UART_SCR_OFFSET     7   /* I/O: Scratch Register */#define UART_MDR1_OFFSET    8   /* I/O:  Mode Register */
#define UART_LSR_FIFOE      0x80    /* Fifo error */#define UART_LSR_TEMT       0x40    /* Transmitter empty */#define UART_LSR_THRE       0x20    /* Transmit-hold-register empty */#define UART_LSR_BI     0x10    /* Break interrupt indicator */#define UART_LSR_FE     0x08    /* Frame error indicator */#define UART_LSR_PE     0x04    /* Parity error indicator */#define UART_LSR_OE     0x02    /* Overrun error indicator */#define UART_LSR_DR     0x01    /* Receiver data ready */#define UART_LSR_BRK_ERROR_BITS 0x1E    /* BI, FE, PE, OE bits */
/* clang-format on */
static volatile char *xxx_uart_base;static u32 xxx_uart_in_freq;static u32 xxx_uart_baudrate;static u32 xxx_uart_reg_width;static u32 xxx_uart_reg_shift;
static u32 get_reg(u32 num){    u32 offset = num << xxx_uart_reg_shift;
    if (xxx_uart_reg_width == 1)        return readb(xxx_uart_base + offset);    else if (xxx_uart_reg_width == 2)        return readw(xxx_uart_base + offset);    else        return readl(xxx_uart_base + offset);}
static void set_reg(u32 num, u32 val){    u32 offset = num << xxx_uart_reg_shift;
    if (xxx_uart_reg_width == 1)        writeb(val, xxx_uart_base + offset);    else if (xxx_uart_reg_width == 2)        writew(val, xxx_uart_base + offset);    else        writel(val, xxx_uart_base + offset);}
static void xxx_uart_putc(char ch){    while ((get_reg(UART_LSR_OFFSET) & UART_LSR_THRE) == 0)        ;
    set_reg(UART_THR_OFFSET, ch);}
static int xxx_uart_getc(void){    if (get_reg(UART_LSR_OFFSET) & UART_LSR_DR)        return get_reg(UART_RBR_OFFSET);    return -1;}
static struct sbi_console_device xxx_uart_console = {    .name = "xxx_uart",    .console_putc = xxx_uart_putc,    .console_getc = xxx_uart_getc};
int xxx_uart_init(unsigned long base, u32 in_freq, u32 baudrate, u32 reg_shift,          u32 reg_width, u32 reg_offset){    u16 bdiv = 0;    volatile uint32_t* tmp = (uint32_t*)0x10000004;    *tmp = 0x11223344;    if(*tmp != 0x11223344)    {        while(1);    }    xxx_uart_base      = (volatile char *)base + reg_offset;    xxx_uart_reg_shift = reg_shift;    xxx_uart_reg_width = reg_width;    xxx_uart_in_freq   = in_freq;    xxx_uart_baudrate  = baudrate;
    if (xxx_uart_baudrate) {        bdiv = (xxx_uart_in_freq + 8 * xxx_uart_baudrate) /               (16 * xxx_uart_baudrate);    }
    /* Disable all interrupts */    set_reg(UART_IER_OFFSET, 0x00);    /* Enable DLAB */    set_reg(UART_LCR_OFFSET, 0x80);
    if (bdiv) {        /* Set divisor low byte */        set_reg(UART_DLL_OFFSET, bdiv & 0xff);        /* Set divisor high byte */        set_reg(UART_DLM_OFFSET, (bdiv >> 8) & 0xff);    }
    /* 8 bits, no parity, one stop bit */    set_reg(UART_LCR_OFFSET, 0x03);    /* Enable FIFO */    set_reg(UART_FCR_OFFSET, 0x01);    /* No modem control DTR RTS */    set_reg(UART_MCR_OFFSET, 0x00);    /* Clear line status */    get_reg(UART_LSR_OFFSET);    /* Read receive buffer */    get_reg(UART_RBR_OFFSET);    /* Set scratchpad */    set_reg(UART_SCR_OFFSET, 0x00);
    sbi_console_set_device(&xxx_uart_console);
    return sbi_domain_root_add_memrange(base, PAGE_SIZE, PAGE_SIZE,                        (SBI_DOMAIN_MEMREGION_MMIO |                        SBI_DOMAIN_MEMREGION_SHARED_SURW_MRW));}

lib/utils/serial/fdt_serial_xxx.c内容如下

/* * SPDX-License-Identifier: BSD-2-Clause * * Copyright (c) . * * Authors: *    */
#include #include #include 
static int serial_xxx_init(const void *fdt, int nodeoff,                const struct fdt_match *match){    int rc;    struct platform_uart_data uart = { 0 };
    rc = fdt_parse_uart_node(fdt, nodeoff, &uart);    if (rc)        return rc;
    return xxx_uart_init(uart.addr, uart.freq, uart.baud,                 uart.reg_shift, uart.reg_io_width,                 uart.reg_offset);}
static const struct fdt_match serial_xxx_match[] = {    { .compatible = "xxx,xxx-uart" },    { },};
struct fdt_serial fdt_serial_xxx = {    .match_table = serial_xxx_match,    .init = serial_xxx_init,};

添加include/sbi_utils/serial/xxx-uart.h文件

内容如下

/* * SPDX-License-Identifier: BSD-2-Clause * * Copyright (c) 2022  Technology Co., Ltd. * * Author:  */
#ifndef __SERIAL_XXX_UART_H__#define __SERIAL_XXX_UART_H__
#include 
int xxx_uart_init(unsigned long base, u32 in_freq, u32 baudrate);
#endif

1. 配置Kconfig

lib/utils/serial/Kconfig

config FDT_SERIAL_XILINX_UARTLITE后添加

config FDT_SERIAL_XXX

bool "XXX UART FDT driver"

select SERIAL_XXX

default n

config SERIAL_XILINX_UARTLITE后添加

config SERIAL_XXX

bool "XXX UART support"

default n

3.配置objects.mk

lib/utils/serial/objects.mk

添加

carray-fdt_serial_drivers-$(CONFIG_FDT_SERIAL_XXX) += fdt_serial_xxx

libsbiutils-objs-$(CONFIG_FDT_SERIAL_XXX) += serial/fdt_serial_xxx.o

libsbiutils-objs-$(CONFIG_SERIAL_XXX) += serial/xxx-uart.o

4.修改设备树

uart@10000000 {

的compatible改为和

lib/utils/serial/fdt_serial_xxx.c中的serial_xxx_match一致

static const struct fdt_match serial_xxx_match[] = {

{ .compatible = "xxx,xxx-uart" },

{ },

};

chosen {    bootargs = [00];    stdout-path = "/uart@10000000";  };
  uart@10000000 {    interrupts = <0x0a>;    interrupt-parent = <0x03>;    clock-frequency = <1000000>;    current-speed = <115200>;    reg-shift = <0>;    reg-io-width = <32>;    reg-offset = <0>;    reg = <0x00 0x10000000 0x00 0x100>;    compatible = "xxx,xxx-uart";  };

编译设备树

dtc -I dts -O dtb -o xxx-uart.dtb platform/generic/qemu_dump.dts

5.编译

export CROSS_COMPILE=~/buildroot/thead_920v2_enhanced_5.10_glibc_br_defconfig/host/bin/riscv64-unknown-linux-gnu-

export PLATFORM_RISCV_XLEN=64

make PLATFORM=generic menuconfig

Utils and Drivers Support --->

Serial Device Support--->

make PLATFORM=generic FW_TEXT_START=0x80000000 FW_FDT_PATH=/home/qinyunti/opensbi/platform/generic/xxx-uart.dtb

运行即可看到qemu的打印。

四. 标准输入输出重定向

4.1 输入输出接口

前面看到了打印，继续来看下，打印是如何实现的

串口初始化时注册底层读写接口

sbi_console_set_device(&xxx_uart_console);

static struct sbi_console_device xxx_uart_console = {

.name = "xxx_uart",

.console_putc = xxx_uart_putc,

.console_getc = xxx_uart_getc

};

还可以实现console_puts打印字符串可以提高效率。

lib/sbi/sbi_console.c中设置全局变量

console_dev = dev;

sbi_printf->print->printc->sbi_putc->nputs_all->nputs->console_dev->console_putc或者console_dev->console_puts

sbi_ecall_dbcn_handler->sbi_ngets/sbi_gets->sbi_getc->console_dev->console_getc

4.2 打印信息

这里来看下相关信息是在哪打印的

以下BUILD_INFO=y可以打印更多信息

make PLATFORM=generic FW_TEXT_START=0x80000000 FW_FDT_PATH=/home/qinyunti/opensbi/platform/generic/xxx-uart.dtb BUILD_INFO=y

Makefile中

# Build Info:# OPENSBI_BUILD_TIME_STAMP -- the compilation time stamp# OPENSBI_BUILD_COMPILER_VERSION -- the compiler version infoBUILD_INFO ?= nifeq ($(BUILD_INFO),y)OPENSBI_BUILD_DATE_FMT = +%Y-%m-%d %H:%M:%S %zifdef SOURCE_DATE_EPOCH    OPENSBI_BUILD_TIME_STAMP ?= $(shell date -u -d "@$(SOURCE_DATE_EPOCH)" \        "$(OPENSBI_BUILD_DATE_FMT)" 2>/dev/null || \        date -u -r "$(SOURCE_DATE_EPOCH)" \        "$(OPENSBI_BUILD_DATE_FMT)" 2>/dev/null || \        date -u "$(OPENSBI_BUILD_DATE_FMT)")else    OPENSBI_BUILD_TIME_STAMP ?= $(shell date "$(OPENSBI_BUILD_DATE_FMT)")endifOPENSBI_BUILD_COMPILER_VERSION=$(shell $(CC) -v 2>&1 | grep ' version ' | \    sed 's/[[:space:]]*$$//')endif

ifeq ($(BUILD_INFO),y)GENFLAGS    +=  -DOPENSBI_BUILD_TIME_STAMP="\"$(OPENSBI_BUILD_TIME_STAMP)\""GENFLAGS    +=  -DOPENSBI_BUILD_COMPILER_VERSION="\"$(OPENSBI_BUILD_COMPILER_VERSION)\""endif
ifeq ($(BUILD_INFO),y)$(build_dir)/lib/sbi/sbi_init.o: $(libsbi_dir)/sbi_init.c FORCE    $(call compile_cc,$@,$<)endif

lib/sbi/sbi_init.c

中

sbi_boot_print_banner打印LOGO和编译版本信息

OPENSBI_BUILD_TIME_STAMP和OPENSBI_BUILD_COMPILER_VERSION就是BUILD_INFO=y时自动生成。

static void sbi_boot_print_banner(struct sbi_scratch *scratch){    if (scratch->options & SBI_SCRATCH_NO_BOOT_PRINTS)        return;
#ifdef OPENSBI_VERSION_GIT    sbi_printf("\nOpenSBI %s\n", OPENSBI_VERSION_GIT);#else    sbi_printf("\nOpenSBI v%d.%d\n", OPENSBI_VERSION_MAJOR,           OPENSBI_VERSION_MINOR);#endif
#ifdef OPENSBI_BUILD_TIME_STAMP    sbi_printf("Build time: %s\n", OPENSBI_BUILD_TIME_STAMP);#endif
#ifdef OPENSBI_BUILD_COMPILER_VERSION    sbi_printf("Build compiler: %s\n", OPENSBI_BUILD_COMPILER_VERSION);#endif
    sbi_printf(BANNER);}

打印如下

五. 总结

串口驱动的实现实际是通过脚本，将各个串口驱动c文件中的struct fdt_serial全局变量，自动组合生成一个全局数组fdt_serial_drivers，该数组的成员就是各个串口驱动的实现struct fdt_serial。通过全局变量fdt_serial_drivers即可索引各个驱动，通过设备树节点的compatible来匹配驱动。

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