sysfs接口函数的建立_DEVICE_ATTR

sysfs接口函数的建立_DEVICE_ATTR

2012-08-08 15:02 by superlcc, 11073 阅读, 0 评论, 收藏, 编辑

sysfs接口函数到建立_DEVICE_ATTR

最近在弄Sensor驱动，看过一个某厂家的成品驱动，里面实现的全都是sysfs接口，hal层利用sysfs生成的接口，对Sensor进行操作。
说道sysfs接口，就不得不提到函数宏 DEVICE_ATTR
原型是#define DEVICE_ATTR(_name, _mode, _show, _store)
\
struct device_attribute dev_attr_##_name = __ATTR(_name,
_mode, _show, _store)

函数宏DEVICE_ATTR内封装的是__ATTR(_name,_mode,_show,_stroe)方法，_show表示的是读方法，_stroe表示的是写方法。
当然_ATTR不是独生子女，他还有一系列的姊妹__ATTR_RO宏只有读方法，__ATTR_NULL等等
如 对设备的使用 DEVICE_ATTR ，对总线使用 BUS_ATTR ，对驱动使用 DRIVER_ATTR ，对类
别 (class) 使用 CLASS_ATTR, 这四个高级的宏来自于<include/linux/device.h>
DEVICE_ATTR 宏声明有四个参数，分别是名称、权限位、读函数、写函数。其中读函数和写函数是读写功能函数的函数名。
如果你完成了DEVICE_ATTR函数宏的填充，下面就需要创建接口了
例如：
static DEVICE_ATTR(polling, S_IRUGO | S_IWUSR, show_polling,
set_polling);

static struct attribute *dev_attrs[] = {

&dev_attr_polling.attr,

NULL,

};

当你想要实现的接口名字是polling的时候，需要实现结构体struct attribute *dev_attrs[]
其中成员变量的名字必须是&dev_attr_polling.attr
然后再封装
static struct attribute_group dev_attr_grp
= {

.attrs = dev_attrs,

};

在利用sysfs_create_group(&pdev->dev.kobj, &dev_attr_grp);创建接口
通 过以上简单的三个步骤，就可以在adb shell 终端查看到接口了。当我们将数据 echo 到接口中时，在上层实际上完成了一次 write 操
作，对应到 kernel ，调用了驱动中的 “store”。同理，当我们cat 一个 接口时则会调用 “show” 。到这里，只是简单的建立 了 android 层到 kernel 的桥梁，真正实现对硬件操作的，还是在 "show" 和 "store" 中完成的。

######################################################################
以下来个例子：

/*

* Sample kobject implementation

*

* Copyright (C) 2004-2007 Greg Kroah-Hartman <greg@kroah.com>

* Copyright (C) 2007 Novell Inc.

*

* Released under the GPL version 2 only.

*

*/

#include <linux/kobject.h>

#include <linux/string.h>

#include <linux/sysfs.h>

#include <linux/module.h>

#include <linux/init.h>

#include <asm/gpio.h>

#include <linux/delay.h>

/*

* This module shows how to create a simple subdirectory in sysfs called

* /sys/kernel/kobject-example In that directory, 3 files are created:

* "foo", "baz", and "bar". If an integer is written to these files, it can be

* later read out of it.

*/

static int foo;

/*

* The "foo" file where a static variable is read from and written to.

*/

static struct msm_gpio qup_i2c_gpios_io[] = {

{ GPIO_CFG(60, 0, GPIO_CFG_OUTPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),

"qup_scl" },

{ GPIO_CFG(61, 0, GPIO_CFG_INPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),

"qup_sda" },

{ GPIO_CFG(131, 0, GPIO_CFG_OUTPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),

"qup_scl" },

{ GPIO_CFG(132, 0, GPIO_CFG_INPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),

"qup_sda" },

};

static struct msm_gpio qup_i2c_gpios_hw[] = {

{ GPIO_CFG(60, 1, GPIO_CFG_INPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),

"qup_scl" },

{ GPIO_CFG(61, 1, GPIO_CFG_INPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),

"qup_sda" },

{ GPIO_CFG(131, 2, GPIO_CFG_INPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),

"qup_scl" },

{ GPIO_CFG(132, 2, GPIO_CFG_INPUT, GPIO_CFG_NO_PULL, GPIO_CFG_8MA),

"qup_sda" },

};

static void gsbi_qup_i2c_gpio_config(int adap_id, int config_type)

{

int rc;

if (adap_id < 0 || adap_id > 1)

return;

/* Each adapter gets 2 lines from the table */

if (config_type)

rc = msm_gpios_enable(&qup_i2c_gpios_hw[adap_id*2], 2);

else

rc = msm_gpios_enable(&qup_i2c_gpios_io[adap_id*2], 2);

if (rc < 0)

pr_err("QUP GPIO request/enable failed: %d\n", rc);

}

static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr,

char *buf)

{

return sprintf(buf, "%d\n", foo);

}

static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr,

const char *buf, size_t count)

{

int sda,scl;

int i;

sscanf(buf, "%du", &foo);

printk("foo = %d.\n",foo);

foo = foo -1;

if (foo < 0 || foo > 1)

{

printk("input foo error. foo=%d.\n",foo);

return 0;

}

sda = GPIO_PIN((&qup_i2c_gpios_hw[foo*2+1])->gpio_cfg);

scl = GPIO_PIN((&qup_i2c_gpios_hw[foo*2])->gpio_cfg);

printk("sda = %d.\n",sda);

printk("scl = %d.\n",scl);

gsbi_qup_i2c_gpio_config(foo,0);

for(i=0;i<9;i++)

{

if(gpio_get_value(sda))

{

printk("sda of i2c%d is high when %d pulse is output on scl.\n",foo,i);

break;

}

gpio_set_value(scl,0);

udelay(5);

gpio_set_value(scl,1);

udelay(5);

}

gsbi_qup_i2c_gpio_config(foo,1);

printk("finish.\n");

return count;

}

static struct kobj_attribute foo_attribute =

__ATTR(i2c_unlock, 0666, foo_show, foo_store);

/*

* Create a group of attributes so that we can create and destroy them all

* at once.

*/

static struct attribute *attrs[] = {

&foo_attribute.attr,

NULL,» /* need to NULL terminate the list of attributes */

};

/*

* An unnamed attribute group will put all of the attributes directly in

* the kobject directory. If we specify a name, a subdirectory will be

* created for the attributes with the directory being the name of the

* attribute group.

*/

static struct attribute_group attr_group = {

.attrs = attrs,

};

static struct kobject *example_kobj;

static int __init example_init(void)

{

int retval;

/*

* Create a simple kobject with the name of "kobject_example",

* located under /sys/kernel/

*

* As this is a simple directory, no uevent will be sent to

* userspace. That is why this function should not be used for

* any type of dynamic kobjects, where the name and number are

* not known ahead of time.

*/

example_kobj = kobject_create_and_add("i2c_recovery", kernel_kobj);

if (!example_kobj)

return -ENOMEM;

/* Create the files associated with this kobject */

retval = sysfs_create_group(example_kobj, &attr_group);

if (retval)

kobject_put(example_kobj);

return retval;

}

static void __exit example_exit(void)

{

kobject_put(example_kobj);

}

module_init(example_init);

module_exit(example_exit);

MODULE_LICENSE("GPL");

MODULE_AUTHOR("Wupeng");

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