Linux设备树的驱动开辟
概述本文介绍了platform框架下的设备驱动开辟流程和方法，主要包罗设备树、驱动程序和应用程序的开辟。以随机数驱动为例，实现了应用程序调用库函数，通过体系调用陷入内核，最后实行硬件驱动，获取真随机数的过程。
添加设备树节点
在soc节点下添加名为trng子节点，内容如下：
trng: trng@0x53030000 {
compatible = "acme,trng";
reg = <0x00 0x53030000 0x00 0x1000>;
interrupts = <0x34 IRQ_TYPE_LEVEL_HIGH>;
interrupt-parent = <&plic>;
};
编译设备树dts，生成相应的dtb文件：
make dtbs
使用新的dtb启动Linux内核。Linux启动成功之后查看是否有trng这个节点：
ls /proc/device-tree/soc
# trng@0x53030000
进入trng目录，查看属性相关的文件：
/proc/device-tree/soc/trng@0x53030000# ls
compatible interrupts phandle
interrupt-parentname reg
编写设备驱动
Makefile
新建trng/driver目录，并创建Makefile，内如如下：
# 内核架构
ARCH := riscv
# 交叉工具链
CROSS_COMPILE := /path/to/riscv32-linux-
# 内核目录
KERNELDIR := /path/to/linux/linux-6.1
# 当前目录
PWD := $(shell pwd)
# 目标文件
obj-m := trng.o
# 目标
build: kernel_modules
# 编译模块
kernel_modules:
$(MAKE) ARCH=$(ARCH) CROSS_COMPILE=$(CROSS_COMPILE) -C $(KERNELDIR) M=$(PWD) modules
# 清理
clean:
$(MAKE) ARCH=$(ARCH) CROSS_COMPILE=$(CROSS_COMPILE) -C $(KERNELDIR) M=$(PWD) clean
驱动
在trng/driver下新建trng.c文件，内容如下：
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/fs.h>
#include <linux/of.h>
#include <linux/cdev.h>
#include <linux/io.h>
#include <linux/iopoll.h>
#include <linux/platform_device.h>
/* TRNG寄存器 */
#define TRNG_CTRL (0x0)
#define TRNG_CTRL_CMD_MASK (0x07)
#define TRNG_CTRL_CMD_RNG (0x01)
#define TRNG_CTRL_CMD_SEED (0x02)
#define TRNG_STAT (0x4)
#define TRNG_STAT_SEEDED BIT(9)
#define TRNG_MODE (0x8)
#define TRNG_MODE_R256 BIT(3)
#define TRNG_ISTAT (0x14)
#define TRNG_ISTAT_RAND_RDY BIT(0)
#define TRNG_ISTAT_SEED_DONE BIT(1)
#define TRNG_RAND0 (0x20)
#define TRNG_TIMEOUT (50000)
#define DRIVER_NAME "trng"
struct trng_dev {
dev_t devid; /* 设备号 */
struct cdev cdev; /* cdev */
struct class *class; /* 类 */
struct device *dev; /* 设备 */
int major; /* 主设备号 */
int minor; /* 次设备号 */
int irq; /* 中断号 */
void __iomem *base; /* 基地址 */
};
static int trng_init(void *base)
{
int ret;
unsigned int value;
/* 模式 */
value = readl(base + TRNG_MODE);
value |= TRNG_MODE_R256;
writel(value, base + TRNG_MODE);
/* 播种 */
value = readl(base + TRNG_CTRL);
value &= ~TRNG_CTRL_CMD_MASK;
value |= TRNG_CTRL_CMD_SEED;
writel(value, base + TRNG_CTRL);
/* 等待播种完成 */
ret = readl_relaxed_poll_timeout_atomic(base + TRNG_ISTAT,
value, (value & TRNG_ISTAT_SEED_DONE),
10, TRNG_TIMEOUT);
if (ret == 0) {
value |= TRNG_ISTAT_SEED_DONE;
writel(value, base + TRNG_ISTAT);
}
return ret;
}
static int trng_generate_random(void *base, unsigned char *buf)
{
int ret;
unsigned int value;
/* 启动生成随机数 */
value = readl(base + TRNG_CTRL);
value &= ~TRNG_CTRL_CMD_MASK;
value |= TRNG_CTRL_CMD_RNG;
writel(value, base + TRNG_CTRL);
/* 等待随机数准备好 */
ret = readl_relaxed_poll_timeout_atomic(base + TRNG_ISTAT,
value, (value & TRNG_ISTAT_RAND_RDY),
10, TRNG_TIMEOUT);
if (ret) {
return ret;
}
/* 清除准备好标志 */
value = readl(base + TRNG_ISTAT);
value &= ~TRNG_ISTAT_RAND_RDY;
writel(value, base + TRNG_ISTAT);
/* 读取随机数 */
for (int i = 0; i < 8; i++) {
*(unsigned int*)buf = readl(base + TRNG_RAND0 + i*4);
buf += 4;
}
return 0;
}
static irqreturn_t trng_irq_handler(int irq, void *dev_id)
{
struct trng_dev *trng;
trng = (struct trng_dev*)dev_id;
dev_dbg(trng->dev, "TRNG interrupt received\n");
return IRQ_HANDLED;
}
static int trng_open(struct inode *inode, struct file *filp)
{
int ret;
struct trng_dev *trng;
trng = container_of(inode->i_cdev, struct trng_dev, cdev);
filp->private_data = trng;
dev_dbg(trng->dev, "Open trng\n");
ret = trng_init(trng->base);
if (ret) {
dev_err(trng->dev, "Failed to init trng, ret=%d\n", ret);
return ret;
}
return 0;
}
static int trng_release(struct inode *inode, struct file *filp)
{
struct trng_dev *trng;
trng = filp->private_data;
dev_dbg(trng->dev, "Release trng\n");
return 0;
}
static ssize_t trng_read(struct file *filp, char __user *buffer, size_t len, loff_t *offset)
{
int ret;
unsigned char random;
size_t copyed_len, len_to_copy;
struct trng_dev *trng;
trng = filp->private_data;
dev_info(trng->dev, "Read trng\n");
copyed_len = 0;
while (len) {
ret = trng_generate_random(trng->base, random);
if (ret) {
dev_err(trng->dev, "Failed to generate random, ret=%d\n", ret);
return ret;
}
// print_hex_dump(KERN_INFO, "random: ", DUMP_PREFIX_NONE, 16, 1, random, sizeof(random), false);
len_to_copy = (len < sizeof(random)) ? len : sizeof(random);
ret = copy_to_user(buffer, random, len_to_copy);
if (ret) {
dev_err(trng->dev, "Failed to copy to user\n");
return -EFAULT;
}
copyed_len += len_to_copy;
buffer += len_to_copy;
len -= len_to_copy;
}
return copyed_len;
}
static ssize_t trng_write(struct file *filp, const char __user *buffer, size_t len, loff_t *offset)
{
struct trng_dev *trng;
trng = filp->private_data;
dev_dbg(trng->dev, "Write trng\n");
return len;
}
static long trng_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
struct trng_dev *trng;
trng = filp->private_data;
dev_dbg(trng->dev, "Ioctl trng\n");
switch (cmd) {
default:
dev_err(trng->dev, "Unknown ioctl = 0x%x\n", cmd);
break;
}
return -ENOTTY;
}
static int trng_mmap(struct file *filp, struct vm_area_struct *vma)
{
struct trng_dev *trng;
trng = filp->private_data;
dev_dbg(trng->dev, "Mmap trng\n");
return 0;
}
static const struct file_operations trng_fops = {
.owner = THIS_MODULE,
.open = trng_open,
.release = trng_release,
.read = trng_read,
.write = trng_write,
.unlocked_ioctl = trng_ioctl,
.mmap = trng_mmap,
};
static int trng_probe(struct platform_device *pdev)
{
struct device *dev = &pdev->dev;
struct trng_dev *trng;
int ret;
/* 分配内存 */
trng = devm_kzalloc(dev, sizeof(*trng), GFP_KERNEL);
if (!trng) {
dev_err(dev, "Failed to allocate memory\n");
return -ENOMEM;
}
/* 将设备的资源映射到内存空间 */
trng->base = devm_platform_ioremap_resource(pdev, 0);
if (IS_ERR(trng->base)) {
dev_err(dev, "Failed to map device registers\n");
return PTR_ERR(trng->base);
}
/* 获取设备的中断号 */
trng->irq = platform_get_irq(pdev, 0);
if (trng->irq <= 0) {
dev_err(dev, "Failed to get irq %d\n", trng->irq);
return trng->irq;
}
/* 请求中断 */
ret = devm_request_irq(dev, trng->irq, trng_irq_handler, 0,
DRIVER_NAME, trng);
if (ret) {
dev_err(dev, "Failed to request IRQ\n");
return ret;
}
/* 申请设备号 */
ret = alloc_chrdev_region(&trng->devid, 0, 1, DRIVER_NAME);
if (ret < 0) {
dev_err(dev, "Failed to allocate device number\n");
return ret;
}
trng->major = MAJOR(trng->devid);
trng->minor = MINOR(trng->devid);
/* 初始化cdev */
trng->cdev.owner = THIS_MODULE;
cdev_init(&trng->cdev, &trng_fops);
/* 添加一个cdev */
ret = cdev_add(&trng->cdev, trng->devid, 1);
if (ret < 0) {
dev_err(dev, "Failed to add cdev\n");
unregister_chrdev_region(trng->devid, 1);
return ret;
}
/* 创建类 */
trng->class = class_create(THIS_MODULE, DRIVER_NAME);
if (IS_ERR(trng->class)) {
cdev_del(&trng->cdev);
unregister_chrdev_region(trng->devid, 1);
dev_err(dev, "Failed to create class\n");
return PTR_ERR(trng->class);
}
/* 创建设备 */
trng->dev = device_create(trng->class, NULL, trng->devid, NULL, DRIVER_NAME);
if (IS_ERR(trng->dev)) {
cdev_del(&trng->cdev);
unregister_chrdev_region(trng->devid, 1);
class_destroy(trng->class);
dev_err(dev, "Failed to create device\n");
return PTR_ERR(trng->dev);
}
/* 保存设备私有结构体 */
platform_set_drvdata(pdev, trng);
dev_info(dev, "TRNG platform driver probed\n");
return 0;
}
static int trng_remove(struct platform_device *pdev)
{
struct trng_dev *trng;
/* 获取设备私有结构体 */
trng = platform_get_drvdata(pdev);
/* 删除cdev */
cdev_del(&trng->cdev);
/* 释放设备号 */
unregister_chrdev_region(trng->devid, 1);
/* 删除设备 */
device_destroy(trng->class, trng->devid);
/* 删除类 */
class_destroy(trng->class);
/* 释放设备内存 */
// devm_kfree(&pdev->dev, trng); // devm_kzalloc为设备分配的内存，在设备移除时会自动释放
dev_info(&pdev->dev, "TRNG platform driver removed\n");
return 0;
}
static const struct of_device_id trng_of_match[] = {
{ .compatible = "acme,trng" },
{ /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, trng_of_match);
static struct platform_driver trng_driver = {
.driver = {
.name = DRIVER_NAME,
.of_match_table = trng_of_match,
},
.probe = trng_probe,
.remove = trng_remove,
};
module_platform_driver(trng_driver);
MODULE_AUTHOR("Author");
MODULE_DESCRIPTION("Trng driver");
MODULE_LICENSE("GPL");
使用platform平台驱动设备模型编写trng的驱动程序。
[*] 当设备树中的节点与驱动匹配成功会实行trng_probe函数，完成驱动的加载。
[*] 当应用需要获取随机数时，读取这个trng设备，陷入内核调用函数trng_read，进而调用函数trng_generate_random完成从硬件获取随机数。
[*] 如果需要释放设备，会调用trng_remove函数卸载设备驱动。
实行make编译驱动程序，编译成功生成trng.ko。
Linux启动成功之后，可以挂载nfs，将trng.ko拷贝到trng目录：
mkdir trng
mount -t nfs -o nolock xx.xx.xx.xx:/nfs/trng /root/trng
实行如下命令，加载设备驱动：
insmod trng.ko
# trng 53030000.trng: TRNG platform driver probed
如果设备驱动加载成功，可以在/dev下找到设备：
ls /dev/trng
另外可以查看trng的设备号：
cat /proc/devices
# 249 trng
如果需要卸载设备驱动，实行：
rmmod trng.ko
# [ 2947.495906] trng 53030000.trng: TRNG platform driver removed
应用App
Makefile
新建trng/app目录，并创建Makefile，内如如下：
# 交叉工具链
CROSS_COMPILE ?= /opt/andestech/nds32le-linux-glibc-v5d/bin/riscv32-linux-
# 指定C编译器
CC := $(CROSS_COMPILE)gcc
# 目标文件名
TARGET := trng
# 源文件名
SRC := trng.c
# 默认目标
all: $(TARGET)
# 编译并链接
$(TARGET): $(SRC)
$(CC) $(SRC) -o $(TARGET)
# 清理
clean:
rm -f $(TARGET)
应用
在trng/app下新建trng.c文件，内容如下：
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#define TRNG_DEVICE "/dev/trng"
static void hexdump(const char *name, const unsigned char *buffer, unsigned int len)
{
printf("****************%s****************\n", name);
for (unsigned int i = 0; i < len; i++) {
printf("%02x ", buffer);
if ((i + 1) % 16 == 0) {
printf("\n");
}
}
if (len % 16 ) {
printf("\n");
}
}
int main(int argc, char *argv[])
{
uint8_t *buf = NULL;
size_t num;
int ret, fd;
if (argc < 2) {
printf("Usage: trng <num>\n");
return -1;
}
num = atoi(argv);
buf = malloc(num);
if (buf == NULL) {
printf("Failed to malloc\n");
return -1;
}
/* 打开设备 */
fd = open(TRNG_DEVICE, O_RDONLY);
if (fd < 0) {
printf("Failed to open trng device\n");
goto exit;
}
/* 读取随机数 */
ret = read(fd, buf, num);
if (ret < 0) {
printf("Failed to read random, ret=%d\n", ret);
goto exit;
}
hexdump("random", buf, num);
exit:
close(fd);
free(buf);
return ret;
}
实行make编译应用程序，编译成功生成trng。
同理，将trng应用拷贝到trng目录，并实行：
./trng 16
# ****************random****************
# 6c 95 ea 3c a0 1f e8 c2 03 db 66 f6 19 4b 07 e3
# c0 96 a3 93 20 a9 68 c5 9f 1f a1 55 c0 9c 24 c9
# 5f 06 47 45 be 2c 21 b5 11 23 23 e6 36 94 3f d6
# 9a 30 68 91 da c4 6d ff af 46 26 c9 ab f8 79 7c
如果随机数获取成功，说明驱动和应用程序运行正常。
编译进内核
在开辟前期阶段，一样平常将驱动编译成模块，方便调试。当驱动开辟完成后，可以将其编译进内核。
驱动
在linux-6.1/drivers下新建trng目录，并创建Makefile和Kconfig文件，内容分别如下：
# SPDX-License-Identifier: GPL-2.0
#
# Makefile for the TRNG device drivers.
#
obj-$(CONFIG_TRNG) := trng.o
# SPDX-License-Identifier: GPL-2.0-only
#
# TRNG device configuration
#
config TRNG
tristate "TRNG support"
help
This driver provides support for TRNG in SoCs.
To compile this driver as a module, choose M here: the module
will be called acme-trng.
If unsure, say Y.
在linux/drivers/Makefile中添加：
obj-$(CONFIG_TRNG) += trng/
在linux/drivers/Kconfig中添加：
source "drivers/trng/Kconfig"
将trng.c驱动文件拷贝到trng目录，最终目录文件如下：
$ tree linux-6.1/drivers/trng/
├── Kconfig
├── Makefile
└── trng.c
内核配置
配置内核，输入命令：
make menuconfig
选择Device Drivers->TRNG support，选择将trng编译进内核，这里可以有三种选择：
[*]*：将该功能编译进内核
[*]空：不编译该功能
[*]M：将该功能编译成内核中的模块
运行
编译Linux并启动，在启动日记中，如果打印如下，说明TRNG驱动运行正常：
[ 4.974450] trng 53030000.trng: TRNG platform driver probed
可以实行命令，获取随机数：
cat /dev/trng | hexdump -n 32
0000000 df01 f5bc de33 2509 8d16 7b5f 8868 8bea
0000010 40f3 00f2 97a4 324d 03c2 10c8 b943 3d6d
0000020
题目解决
[*] 加载KO报非常trng: loading out-of-tree module taints kernel.
原因在于没有将此驱动模块加入到Kconfig导致。
[*] 使用函数devm_kzalloc为设备分配的内存，在设备移除时会自动释放，可以不进行体现释放devm_kfree
[*] 宏container_of用于从布局体的某个成员的地址反推出整个布局体的地址，尤其留意第一个参数必须为成员的地址，如果布局体成员为指针变量，需要取该指针变量的地址。
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