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:
-
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:
-
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):
-
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:
-
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:
-
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:
-
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。
-
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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