Linux设备驱动开发

设备驱动开发"/>

Linux设备驱动开发

By: fulinux
E-mail: fulinux@sina
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目录

• 概述
• 问题
• hrtimer驱动示例修改版
• Makefile文件
• 运行演示

概述

我觉得这篇文章写的挺好，大家可以看下：Linux内核高精度定时器hrtimer 使用实例
主要是他还附带了示例。

问题

不过上述文章中的示例，我在使用时出现了多出错误的地方，可能是内核版本的区别，首先是hrtimer_test_ioctl函数的区别，主要集中在参数这一块，我看是空的我就给屏蔽了，再就是我执行echo语句时会出现内核错误：

root@msm8937:~# echo 1 > /dev/hrtimer_test 
[  494.983351] hrtimer enter
[  494.983380] hrtimer 48
[  494.984945] hrtimer 50
[  494.987206] Unhandled fault: page domain fault (0x01b) at 0x89371168
[  494.989559] pgd = b82a23a5
[  494.996058] [89371168] *pgd=aa5c3835, *pte=a5f2275f, *ppte=a5f22c7f
[  495.004562] Internal error: : 1b [#5] PREEMPT SMP ARM
[  495.004918] Modules linked in: hello(O) wlan(O) wglink_dlkm(O) usf_dlkm(O) stub_dlkm(O) pinctrl_wcd_dlkm(O) native_dlkm(O) platform_dlkm(O) machine_ext_dlkm(O) wcd9335_dlkm(O) swr_ctrl_dlkm(O) machine_dlkm(O) wsa881x_analog_dlkm(O) wsa881x_dlkm(O) swr_dlkm(O) hdmi_dlkm(O) digital_cdc_dlkm(O) cpe_lsm_dlkm(O) wcd_cpe_dlkm(O) analog_cdc_dlkm(O) wcd9xxx_dlkm(O) mbhc_dlkm(O) wcd_core_dlkm(O) q6_dlkm(O) adsp_loader_dlkm(O) apr_dlkm(O) q6_notifier_dlkm(O) [last unloaded: hello]
[  495.051351] CPU: 0 PID: 1902 Comm: sh Tainted: G      D W  O    4.9.218 #1
[  495.051623] Hardware name: Qualcomm Technologies, Inc. QM215
[  495.058392] task: c2b48f38 task.stack: 3a4e745d
[  495.064212] PC is at kstrtoint+0x24/0xc8
[  495.068464] LR is at hrtimer_test_write+0x74/0x180 [hello]
[  495.072630] pc : [<c053579c>]    lr : [<bf12e110>]    psr: 600d0013
[  495.072630] sp : ebac9e70  ip : ebac9e98  fp : ebac9e94
[  495.077937] r10: 00000004  r9 : 00000000  r8 : ebac9f70
[  495.089294] r7 : 89371168  r6 : bf12e09c  r5 : 89371168  r4 : ebac9ea8
[  495.094506] r3 : 00000000  r2 : 00000000  r1 : 0000000a  r0 : 89371168
[  495.101103] Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
[  495.107614] Control: 10c0383d  Table: aa4d006a  DAC: 00000051
[  495.114814] 
[  495.114814] PC: 0xc053571c:
...

错误原因是使用hrtimer_test_write函数里面的buf就会出错，我换成copy_from_user也是会出现相同问题，于是我换成kstrtoul_from_user函数即可。

hrtimer驱动示例修改版

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/jiffies.h>
#include <linux/hrtimer.h>
#include <linux/miscdevice.h>
#include <linux/uaccess.h>unsigned int timer_count = 0;
struct hrtimer hrtimer_test_timer;
ktime_t m_kt;
int value = 2000;static enum hrtimer_restart hrtimer_test_timer_poll(struct hrtimer *timer)
{printk("timer_count=%d\n", timer_count++);hrtimer_forward(timer, timer->base->get_time(), m_kt);return HRTIMER_RESTART;
}static ssize_t hrtimer_test_write(struct file *fp, const char __user *buf, size_t count, loff_t *ppos)
{int ret = 0;unsigned long val;printk("hrtimer enter\n");printk("hrtimer %d\n", __LINE__);printk("hrtimer count = %d\n", count);ret = kstrtoul_from_user(buf, count, 0, &val);if (ret) {printk("kstrtoint error return %d\n", ret);return -EINVAL;}printk("hrtimer Debug val:%d size:%d\n", val, count);if (val == 1) {printk("hrtimer_start\n");m_kt = ktime_set(value / 1000, (value % 1000) * 1000000);hrtimer_start(&hrtimer_test_timer, m_kt, HRTIMER_MODE_REL);} else {printk("hrtimer_cancel\n");hrtimer_cancel(&hrtimer_test_timer);}printk("hrtimer exit\n");return count;
}static const struct file_operations hrtimer_test_fops = {.owner = THIS_MODULE,.write = hrtimer_test_write,
};static struct miscdevice hrtimer_test_dev = {.minor = MISC_DYNAMIC_MINOR,.name = "hrtimer_test",.fops = &hrtimer_test_fops,
};int init_module(void)
{int ret;printk("Hello World!\n");ret = misc_register(&hrtimer_test_dev);hrtimer_init(&hrtimer_test_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);hrtimer_test_timer.function = hrtimer_test_timer_poll;return 0;
}void cleanup_module(void)
{printk("Goodbye Cruel World!\n");misc_deregister(&hrtimer_test_dev);
}MODULE_LICENSE("GPL");

Makefile文件

obj-m := hello.oSRC := $(shell pwd)all:$(MAKE) -C $(KERNEL_SRC) M=$(SRC)modules_install:$(MAKE) -C $(KERNEL_SRC) M=$(SRC) modules_installclean:rm -f *.o *~ core .depend .*.cmd *.ko *.mod.crm -f Module.markers Module.symvers modules.orderrm -rf .tmp_versions Modules.symvers

运行演示

root:~# insmod hello.ko 
[  928.049913] Hello World!
root:~# echo 1 > /dev/hrtimer_test 
[  930.322295] hrtimer enter
[  930.322326] hrtimer 47
[  930.323892] hrtimer count = 2
[  930.326151] hrtimer Debug val:1 size:2
[  930.329258] hrtimer_start
[  930.334506] hrtimer exit
root:~# 
[  932.334636] timer_count=0
[  934.334649] timer_count=1
[  936.334512] timer_count=2
[  938.334633] timer_count=3
[  940.334513] timer_count=4
[  942.334631] timer_count=5
...
root:~# echo 0 > /dev/hrtimer_test 
root:~# e[  960.334665] timer_count=14
[  964.794608] hrtimer enter
[  964.795294] hrtimer 47
[  964.797980] hrtimer count = 2
[  964.800445] hrtimer Debug val:0 size:2
[  964.803284] hrtimer_cancel
[  964.806932] hrtimer exit