Linux I2C驱动分析(二)----I2C板级设备扫描和数据传输
2015-01-08 16:48
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一、板级设备扫描
针对上一篇博客最后的i2c_scan_static_board_info(adap)函数处,首先先看下在系统启动的时候板级设备的注册。针对我现在使用的开发板,对于I2C设备注册程序如下:
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static struct i2c_board_info i2c_devices_info[]
= {
#ifdef CONFIG_SND_SOC_ALC5623
{
I2C_BOARD_INFO("alc5623", 0x1a),
.platform_data
= &alc5623_data,
},
#endif
#ifdef CONFIG_RTC_DRV_DS3231M
{
I2C_BOARD_INFO("ds3231m", 0x68),
.platform_data
= NULL,
},
#endif
#ifdef CONFIG_RTC_DRV_PCF8563
{
I2C_BOARD_INFO("pcf8563", 0x51),
.platform_data
= NULL,
},
#endif
};
static int __init gsc3280_i2c_devices_init(void)
{
i2c_register_board_info(0, i2c_devices_info,
ARRAY_SIZE(i2c_devices_info));
return 0;
}
device_initcall(gsc3280_i2c_devices_init);
在这里总共有三个I2C设备,名称分别为alc5623、ds3231m和pcf8563。宏I2C_BOARD_INFO的功能就是设置I2C设备的名称和地址,由device_initcall可以看出,gsc3280_i2c_devices_init()函数在系统启动的时候就会被调用,i2c_register_board_info()函数完成板级设备的注册,程序如下:
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DECLARE_RWSEM(__i2c_board_lock);
EXPORT_SYMBOL_GPL(__i2c_board_lock);
LIST_HEAD(__i2c_board_list);
EXPORT_SYMBOL_GPL(__i2c_board_list);
int __i2c_first_dynamic_bus_num;
EXPORT_SYMBOL_GPL(__i2c_first_dynamic_bus_num);
int __init
i2c_register_board_info(int busnum,
struct i2c_board_info const
*info, unsigned
len)
{
int status;
down_write(&__i2c_board_lock);
/* dynamic bus numbers will be assigned after the last static one
*/
if (busnum
>= __i2c_first_dynamic_bus_num)
__i2c_first_dynamic_bus_num = busnum
+ 1;
for (status
= 0;
len; len--, info++)
{
struct i2c_devinfo *devinfo;
devinfo = kzalloc(sizeof(*devinfo),
GFP_KERNEL);
if (!devinfo)
{
pr_debug("i2c-core: can't register boardinfo!\n");
status =
-ENOMEM;
break;
}
devinfo->busnum
= busnum;
devinfo->board_info
= *info;
list_add_tail(&devinfo->list,
&__i2c_board_list);
}
up_write(&__i2c_board_lock);
return status;
}
上面的程序位于i2c-boardinfo.c中,i2c_register_board_info()函数的for循环中,首先会申请I2C设备信息结构体,如果申请成功,将I2C总线号和设备信息赋值给设备信息结构体,并且将设备信息结构体的链表插入到__i2c_board_list中,此处尤为重要,在本文的开头中所提的函数i2c_scan_static_board_info(adap);,此函数就是通过__i2c_board_list链表找到上面注册的设备信息,结合gsc3280_i2c_devices_init()函数和i2c_devices_info结构体,此处for循环的len为3,即正常情况下需要创建三个devinfo结构体,for循环结束后,__i2c_board_list链表中也就有了三个I2C设备的链表项,在程序的其他地方如果需要使用这里注册的设备结构信息,只需要遍历链表__i2c_board_list,通过总线号即可找到相应的设备信息。
接下来就可以看下函数i2c_scan_static_board_info(adap):
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static void i2c_scan_static_board_info(struct i2c_adapter
*adapter)
{
struct i2c_devinfo *devinfo;
down_read(&__i2c_board_lock);
list_for_each_entry(devinfo,
&__i2c_board_list, list)
{
if (devinfo->busnum
== adapter->nr
&&
!i2c_new_device(adapter,
&devinfo->board_info))
dev_err(&adapter->dev,
"Can't create device at 0x%02x\n",
devinfo->board_info.addr);
}
up_read(&__i2c_board_lock);
}
从上面程序可以看到,语句list_for_each_entry(devinfo,
&__i2c_board_list, list)
实现对__i2c_board_list的遍历,if语句的前半部分“devinfo->busnum
== adapter->nr”判断是否是需要寻找的结构体,如果是,就调用函数i2c_new_device()创建新的I2C设备,i2c_new_device函数如下:
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struct i2c_client *
i2c_new_device(struct i2c_adapter
*adap, struct i2c_board_info
const *info)
{
struct i2c_client *client;
int status;
client = kzalloc(sizeof
*client, GFP_KERNEL);
if (!client)
return NULL;
client->adapter
= adap;
client->dev.platform_data
= info->platform_data;
if (info->archdata)
client->dev.archdata
= *info->archdata;
client->flags
= info->flags;
client->addr
= info->addr;
client->irq
= info->irq;
strlcpy(client->name, info->type,
sizeof(client->name));
/* Check
for address validity
*/
status = i2c_check_client_addr_validity(client);
if (status)
{
dev_err(&adap->dev,
"Invalid %d-bit I2C address 0x%02hx\n",
client->flags
& I2C_CLIENT_TEN ? 10
: 7, client->addr);
goto out_err_silent;
}
/* Check
for address business
*/
status = i2c_check_addr_busy(adap, client->addr);
if (status)
goto out_err;
client->dev.parent
= &client->adapter->dev;
client->dev.bus
= &i2c_bus_type;
client->dev.type
= &i2c_client_type;
client->dev.of_node
= info->of_node;
dev_set_name(&client->dev,
"%d-%04x", i2c_adapter_id(adap),
client->addr);
status = device_register(&client->dev);
if (status)
goto out_err;
dev_dbg(&adap->dev,
"client [%s] registered with bus id %s\n",
client->name, dev_name(&client->dev));
return client;
out_err:
dev_err(&adap->dev,
"Failed to register i2c client %s at 0x%02x "
"(%d)\n", client->name, client->addr,
status);
out_err_silent:
kfree(client);
return NULL;
}
EXPORT_SYMBOL_GPL(i2c_new_device);
从函数i2c_new_device()中可以看到,此函数创建了i2c_client结构体,对结构体的内容进行了注册,设备信息进行了填充,对于本文所使用的开发板,如果程序执行正常,系统启动成功后,在内存中就有了三个
i2c_client结构体了,分别对应alc5623、ds3231m和pcf8563。
到此位置,I2C总线驱动,I2C设备的注册和相应结构体的申请就已经完成了,接下来看下常用的I2C数据传输函数,I2C设备驱动主要调用这些数据传输接口完成数据的传输。
二、I2C数据传输
I2C数据传输分为两种,一种为符合I2C协议的普通数据传输,另外一种为符合SMBUS协议的数据传输,接下来我们首先看下符合I2C协议的普通数据传输。
1、I2C协议的普通数据传输
I2C协议普通数据传输的接口函数基本为i2c_master_send和i2c_master_recv,查看其函数发现,最后都是调用i2c_transfer函数实现传输的,i2c_transfer函数如下:
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int i2c_transfer(struct i2c_adapter
* adap, struct i2c_msg
*msgs,
int num)
{
int ret;
if (adap->algo->master_xfer)
{
#ifdef DEBUG
for (ret
= 0; ret
< num; ret++)
{
dev_dbg(&adap->dev,
"master_xfer[%d] %c, addr=0x%02x, "
"len=%d%s/n", ret,
(msgs[ret].flags
& I2C_M_RD)
?
'R' :
'W', msgs[ret].addr,
msgs[ret].len,
(msgs[ret].flags
& I2C_M_RECV_LEN)
? "+"
: "");
}
#endif
if (in_atomic()
|| irqs_disabled())
{
ret = mutex_trylock(&adap->bus_lock);
if
(!ret)
/* I2C activity
is ongoing.
*/
return -EAGAIN;
} else
{
mutex_lock_nested(&adap->bus_lock, adap->level);
}
ret = adap->algo->master_xfer(adap,msgs,num);
mutex_unlock(&adap->bus_lock);
return ret;
} else
{
dev_dbg(&adap->dev,
"I2C level transfers not supported/n");
return -ENOSYS;
}
}
因为在这里的同步用的是mutex。首先判断是否允许睡眠,如果不允许,尝试获锁,如果获锁失败,则返回。这样的操作是避免进入睡眠,我们在后面也可以看到,实际的传输工作交给了adap->algo->master_xfer()完成,也就是我们在(一)中注册的algorithm中的i2c_gsc_func函数。
2、SMBUS协议I2C数据传输
SMBUS协议的具体内容可以参考网络,在I2C驱动中,符合SMBUS协议传输的函数很多,包括i2c_smbus_read_byte、i2c_smbus_write_byte、i2c_smbus_read_byte_data、i2c_smbus_write_byte_data、i2c_smbus_read_word_data和i2c_smbus_write_word_data等,阅读这些函数发现,程序里面都是根据SMBUS协议和函数功能,完成对函数i2c_smbus_xfer形参的赋值,最后调用此函数来实现传输。接下来看下i2c_smbus_xfer函数:
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s32 i2c_smbus_xfer(struct i2c_adapter
*adapter, u16 addr, unsigned short flags,
char read_write, u8 command,
int protocol,
union i2c_smbus_data *data)
{
unsigned long orig_jiffies;
int try;
s32 res;
flags &= I2C_M_TEN
| I2C_CLIENT_PEC;
if (adapter->algo->smbus_xfer)
{
i2c_lock_adapter(adapter);
/* Retry automatically
on arbitration loss
*/
orig_jiffies = jiffies;
for (res
= 0, try
= 0; try <= adapter->retries; try++)
{
res = adapter->algo->smbus_xfer(adapter,
addr, flags,
read_write, command,
protocol, data);
if
(res !=
-EAGAIN)
break;
if
(time_after(jiffies,
orig_jiffies + adapter->timeout))
break;
}
i2c_unlock_adapter(adapter);
} else
res = i2c_smbus_xfer_emulated(adapter, addr, flags, read_write,
command, protocol, data);
return res;
}
如果adapter有smbus_xfer()函数,则直接调用它发送数据。否则也就是在adapter不支持smbus协议的情况下,调用i2c_smbus_xfer_emulated()继续处理。根据(一)中的总线驱动是不支持smbus协议的。继续看函数i2c_smbus_xfer_emulated。
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static s32 i2c_smbus_xfer_emulated(struct i2c_adapter
* adapter, u16 addr,
unsigned short flags,
char read_write, u8 command,
int size,
union i2c_smbus_data
* data)
{
/* So we need
to generate a series of msgs.
In the case of writing, we
need to use only one message; when reading, we need two. We initialize
most things with sane defaults,
to keep the code below somewhat
simpler.
*/
//写操作只会进行一次交互,而读操作,有时会有两次操作.
//因为有时候读操作要先写command,再从总线上读数据
//在这里为了代码的简洁,使用了两个缓存区,将两种情况统一起来.
unsigned char msgbuf0[I2C_SMBUS_BLOCK_MAX+3];
unsigned char msgbuf1[I2C_SMBUS_BLOCK_MAX+2];
//一般来说,读操作要交互两次,例外的情况我们在下面会接着分析
int num = read_write
== I2C_SMBUS_READ?2:1;
//与设备交互的数据,一般在msg[0]存放写入设备的信息,在msb[1]里存放接收到的
//信息,不过也有例外的
//msg[2]的初始化,默认发送缓存区占一个字节,无接收缓存
struct i2c_msg msg[2]
= {
{ addr, flags, 1, msgbuf0
},
{ addr, flags
| I2C_M_RD, 0, msgbuf1
}
};
int i;
u8 partial_pec = 0;
//将要发送的信息copy到发送缓存区的第一字节
msgbuf0[0]
= command;
switch(size)
{
//quick类型,它并不传输有效数据,只是将地址写到总线上,等待应答即可
//所以将发送缓存区长度置为0。再根据读/写操作,调整msg[0]的标志位
//这类传输只需要一次总线交互
case I2C_SMBUS_QUICK:
msg[0].len
= 0;
/* Special
case: The read/write field
is used as data */
msg[0].flags
= flags |
(read_write==I2C_SMBUS_READ)?I2C_M_RD:0;
num = 1;
break;
case I2C_SMBUS_BYTE:
//BYTE类型指一次写和读只有一个字节.这种情况下,读和写都只会交互一次
//这种类型的读有例外,它读取出来的数据不是放在msg[1]中的,而是存放在msg[0]
if (read_write
== I2C_SMBUS_READ)
{
/* Special
case: only a
*/
msg[0].flags
= I2C_M_RD | flags;
num = 1;
}
break;
case I2C_SMBUS_BYTE_DATA:
//Byte_Data是指命令+数据的传输形式,在这种情况下,写只需要一次交互,读却要两次
//第一次将command写到总线上,第二次要转换方向,要将设备地址和read标志写入总线.
//应回答之后再进行read操作
//写操作占两字节,分别是command+data,读操作的有效数据只有一个字节
//交互次数用初始化值就可以了
if (read_write
== I2C_SMBUS_READ)
msg[1].len
= 1;
else {
msg[0].len
= 2;
msgbuf0[1]
= data->byte;
}
break;
case I2C_SMBUS_WORD_DATA:
//Word_Data是指命令+双字节的形式.这种情况跟Byte_Data的情况类似
//两者相比只是交互的数据大小不同
if (read_write
== I2C_SMBUS_READ)
msg[1].len
= 2;
else {
msg[0].len=3;
msgbuf0[1]
= data->word
& 0xff;
msgbuf0[2]
= data->word
>> 8;
}
break;
case I2C_SMBUS_PROC_CALL:
//Proc_Call的方式与write 的Word_Data相似,只不过写完Word_Data之后,要等待它的应答
//应该它需要交互两次,一次写一次读
num = 2;
/* Special
case */
read_write = I2C_SMBUS_READ;
msg[0].len
= 3;
msg[1].len
= 2;
msgbuf0[1]
= data->word
& 0xff;
msgbuf0[2]
= data->word
>> 8;
break;
case I2C_SMBUS_BLOCK_DATA:
//Block_Data:指command+N段数据的情况.
//如果是读操作,它首先要写command到总线,然后再读N段数据,要写的command已经
//放在msg[0]了,现在只需要将msg[1]的标志置I2C_M_RECV_LEN位,msg[1]有效长度为1字节,因为
//adapter驱动会处理好的,现在还不知道要传多少段数据.
//对于写的情况:msg[1]照例不需要.将要写的数据全部都放到msb[0]中.相应的也要更新
//msg[0]中的缓存区长度
if (read_write
== I2C_SMBUS_READ)
{
msg[1].flags
|= I2C_M_RECV_LEN;
msg[1].len
= 1;
/* block length will be added by
the underlying bus driver */
} else
{
//data->block[0]表示后面有多少段数据.总长度要加2是因为command+count+N段数据
msg[0].len
= data->block[0]
+ 2;
if
(msg[0].len
> I2C_SMBUS_BLOCK_MAX
+ 2) {
dev_err(&adapter->dev,
"smbus_access called with "
"invalid block write size (%d)/n",
data->block[0]);
return -1;
}
for
(i = 1; i
< msg[0].len; i++)
msgbuf0 = data->block[i-1];
}
break;
case I2C_SMBUS_BLOCK_PROC_CALL:
//Proc_Call:表示写完Block_Data之后,要等它的应答消息它和Block_Data相比,只是多了一部份应答而已
num = 2;
/* Another special
case */
read_write = I2C_SMBUS_READ;
if (data->block[0]
> I2C_SMBUS_BLOCK_MAX)
{
dev_err(&adapter->dev,
"%s called with invalid "
"block proc call size (%d)/n", __func__,
data->block[0]);
return -1;
}
msg[0].len
= data->block[0]
+ 2;
for (i
= 1; i
< msg[0].len; i++)
msgbuf0 = data->block[i-1];
msg[1].flags
|= I2C_M_RECV_LEN;
msg[1].len
= 1;
/* block length will be added by
the underlying bus driver */
break;
case I2C_SMBUS_I2C_BLOCK_DATA:
//I2c Block_Data与Block_Data相似,只不过read的时候,数据长度是预先定义好了的.另外
//与Block_Data相比,中间不需要传输Count字段.(Count表示数据段数目)
if (read_write
== I2C_SMBUS_READ)
{
msg[1].len
= data->block[0];
} else
{
msg[0].len
= data->block[0]
+ 1;
if
(msg[0].len
> I2C_SMBUS_BLOCK_MAX
+ 1) {
dev_err(&adapter->dev,
"i2c_smbus_xfer_emulated called with "
"invalid block write size (%d)/n",
data->block[0]);
return -1;
}
for
(i = 1; i
<= data->block[0];
i++)
msgbuf0 = data->block;
}
break;
default:
dev_err(&adapter->dev,
"smbus_access called with invalid size (%d)/n",
size);
return -1;
}
//如果启用了PEC.Quick和I2c Block_Data是不支持PEC的
i = ((flags
& I2C_CLIENT_PEC)
&& size
!= I2C_SMBUS_QUICK
&& size
!= I2C_SMBUS_I2C_BLOCK_DATA);
if (i)
{
/* Compute PEC
if first message is a write
*/
//如果第一个操作是写操作
if (!(msg[0].flags
& I2C_M_RD))
{
//如果只是写操作
if
(num == 1)
/* Write only
*/
//如果只有写操作,写缓存区要扩充一个字节,用来存放计算出来的PEC
i2c_smbus_add_pec(&msg[0]);
else
/* Write followed by read
*/
//如果后面还有读操作,先计算前面写部份的PEC(注意这种情况下不需要
//扩充写缓存区,因为不需要发送PEC.只会接收到PEC)
partial_pec = i2c_smbus_msg_pec(0,
&msg[0]);
}
/* Ask
for PEC if last message
is a read */
//如果最后一次是读消息.还要接收到来自slave的PEC.所以接收缓存区要扩充一个字节
if (msg[num-1].flags
& I2C_M_RD)
msg[num-1].len++;
}
if (i2c_transfer(adapter, msg, num)
< 0)
return -1;
/* Check PEC
if last message is a read
*/
//操作完了之后,如果最后一个操作是PEC的读操作.检验后面的PEC是否正确
if (i
&&
(msg[num-1].flags
& I2C_M_RD))
{
if (i2c_smbus_check_pec(partial_pec,
&msg[num-1])
< 0)
return -1;
}
//操作完了,现在可以将数据放到data部份返回了.
if (read_write
== I2C_SMBUS_READ)
switch(size)
{
case I2C_SMBUS_BYTE:
data->byte
= msgbuf0[0];
break;
case I2C_SMBUS_BYTE_DATA:
data->byte
= msgbuf1[0];
break;
case I2C_SMBUS_WORD_DATA:
case I2C_SMBUS_PROC_CALL:
data->word
= msgbuf1[0]
| (msgbuf1[1]
<< 8);
break;
case I2C_SMBUS_I2C_BLOCK_DATA:
for
(i = 0; i
< data->block[0]; i++)
data->block[i+1]
= msgbuf1;
break;
case I2C_SMBUS_BLOCK_DATA:
case I2C_SMBUS_BLOCK_PROC_CALL:
for
(i = 0; i
< msgbuf1[0]
+ 1; i++)
data->block
= msgbuf1;
break;
}
return 0;
}
此处也是调用i2c_transfer函数实现数据的最终传输的,在上面已经讲述了此函数。
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