Github: __set_bit
Email: BuddyZhang1 buddy.zhang@aliyun.com
目录
源码分析
/**
* __set_bit - Set a bit in memory
* @nr: the bit to set
* @addr: the address to start counting from
*
* Unlike set_bit() , this function is non-atomic and may be reordered.
* If it's called on the same region of memory simultaneously, the effect
* may be that only one operation succeeds.
*/
static inline void __set_bit(int nr, volatile unsigned long *addr)
{
unsigned long mask = BIT_MASK(nr);
unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
*p |= mask;
}
__set_bit() 函数用于将 bit 的指定位数置位。参数 nr 指向需要置位的位置;参数
addr 指向 bit 所在的内存位置。函数首先调用 BIT_MASK() 函数获得只有 nr 位置位
的掩码。然后调用 BIT_WORD 函数计算 nr 在 bit 中第几个 long 里,然后将其加上
addr 的地址,以此计算出 p 所在的内存位置,最后将其值与 mask 相与。
实践
驱动源码
/*
* Bitmap.
*
* (C) 2019.06.10 <buddy.zhang@aliyun.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/kernel.h>
#include <linux/init.h>
/* header of bitmap */
#include <linux/bitmap.h>
static __init int bitmap_demo_init ( void )
{
unsigned long bit = 0 ;
/* Set a bit in memory */
__set_bit ( 10 , & bit );
printk ( "Bit: %#lx \n " , bit );
return 0 ;
}
device_initcall ( bitmap_demo_init );
驱动安装
驱动的安装很简单,首先将驱动放到 drivers/BiscuitOS/ 目录下,命名为 bitmap.c,
然后修改 Kconfig 文件,添加内容参考如下:
diff --git a/drivers/BiscuitOS/Kconfig b/drivers/BiscuitOS/Kconfig
index 4edc5a5..1a9abee 100644
--- a/drivers/BiscuitOS/Kconfig
+++ b/drivers/BiscuitOS/Kconfig
@@ -6 ,4 +6,14 @@ if BISCUITOS_DRV
config BISCUITOS_MISC
bool "BiscuitOS misc driver"
+config BISCUITOS_BITMAP
+ bool "bitmap"
+
+if BISCUITOS_BITMAP
+
+config DEBUG_BISCUITOS_BITMAP
+ bool "__set_bit"
+
+endif # BISCUITOS_BITMAP
+
endif # BISCUITOS_DRV
接着修改 Makefile,请参考如下修改:
diff --git a/drivers/BiscuitOS/Makefile b/drivers/BiscuitOS/Makefile
index 82004c9..9909149 100644
--- a/drivers/BiscuitOS/Makefile
+++ b/drivers/BiscuitOS/Makefile
@@ -1 +1,2 @@
obj-$( CONFIG_BISCUITOS_MISC) += BiscuitOS_drv.o
+obj-$( CONFIG_BISCUITOS_BITMAP) += bitmap.o
--
驱动配置
驱动配置请参考下面文章中关于驱动配置一节。在配置中,勾选如下选项,如下:
Device Driver--->
[ * ] BiscuitOS Driver--->
[ * ] bitmap
[ * ] __set_bit()
具体过程请参考:
Linux 5.0 开发环境搭建 – 驱动配置
驱动编译
驱动编译也请参考下面文章关于驱动编译一节:
Linux 5.0 开发环境搭建 – 驱动编译
驱动运行
驱动的运行,请参考下面文章中关于驱动运行一节:
Linux 5.0 开发环境搭建 – 驱动运行
启动内核,并打印如下信息:
usbcore: registered new interface driver usbhid
usbhid: USB HID core driver
Bit: 0x400
aaci-pl041 10004000.aaci: ARM AC'97 Interface PL041 rev0 at 0x10004000, irq 24
aaci-pl041 10004000.aaci: FIFO 512 entries
oprofile: using arm/armv7-ca9
驱动分析
bit 置位。
附录
BiscuitOS Home
BiscuitOS Driver
BiscuitOS Kernel Build
Linux Kernel
Bootlin: Elixir Cross Referencer
搭建高效的 Linux 开发环境
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