i2c总线是嵌入式驱动中不能绕过一个地方，为了更深入的了解linux下的i2c 通信原理，我用一个用户程序 模拟，
这个程序，简单的说就是可以使用一个addr, 一个offset，对i2c 的地址为addr的从设备进行读写访问，访 问的寄存器是这个从设备的寄存器地址为offset。 在我们的版卡上时钟芯片pcf8563的i2c地址为0x51， pcf8563有00—0f个寄存器，通过读写秒，分钟，小时等的寄存器，可以验证我们的程序是否执行成功。 需要pcf8563的datasheet,读者可在网上查找。
我们版卡的cpu是Cavium Networks OCTEON CN52XX
********************************************** *******************************
************ ****************************************************
{
struct pcf8563 *pcf8563 = i2c_get_clientdata(client);
int i, err;
unsigned char buf[9];
printk(KERN_DEBUG "%s: secs=%d, mins=%d, hours=%d,ecs=%d, mins=%d, hours=%d
n",
__func__,
tm->tm_sec, tm->tm_min, tm->tm_hour,
tm->tm_mday, tm->tm_mon, tm->tm_year, tm->tm_wday);
/* hours, minutes and seconds */
buf[PCF8563_REG_SC] = bin2bcd(tm->tm_sec);
buf[PCF8563_REG_MN] = bin2bcd(tm->tm_min);
buf[PCF8563_REG_HR] = bin2bcd(tm->tm_hour);
buf[PCF8563_REG_DM] = bin2bcd(tm->tm_mday);
/* month, 1 - 12 */
buf[PCF8563_REG_MO] = bin2bcd(tm->tm_mon + 1);
/* year and century */
buf[PCF8563_REG_YR] = bin2bcd(tm->tm_year % 100);
if (pcf8563->c_polarity ? (tm->tm_year >= 100) : (tm->tm_year < 100))
buf[PCF8563_REG_MO] |= PCF8563_MO_C;
buf[PCF8563_REG_DW] = tm->tm_wday & 0x07;
/* write register's data */
for (i = 0; i < 7; i++) {
unsigned char data[2] = { PCF8563_REG_SC + i,
buf[PCF8563_REG_SC + i] };
err = i2c_master_send(client, data, sizeof(data));
if (err != sizeof(data)) {
dev_err(&client->dev,
"%s: err=%d addr=%02x, data=%02xn",
__func__, err, data[0], data[1]);
return -EIO;
}
在 driver/i2c/i2c-core.c 中：
int i2c_master_send(struct i2c_client *client,const char *buf ,int count)
{
int ret;
struct i2c_adapter *adap=client->adapter;
struct i2c_msg msg;
msg.addr = client->addr;
msg.flags = client->flags & I2C_M_TEN;
msg.len = count;
msg.buf = (char *)buf;
//added by handwei.2012.7.5
//added by handwei.2012.7.5
printk(KERN_DEBUG "%s: msg.addr = %x,msg.flags = %x,msg.len = %d,msg.buf[0] = %x,msg.
buf[1] = %xn",__func__,msg.addr,msg.flags,msg.len,msg.buf[0],msg.buf[1]);
ret = i2c_transfer(adap, &msg, 1);
/* If everything went ok (i.e. 1 msg transmitted), return #bytes
transmitted, else error code. */
return (ret == 1) ? count : ret;
}
注意： i2c_transfer(adap, &msg, 1);
中的 1 决定了 进入 octeon_i2c_xfer ()后，要进入 if（num==1)中。
下面是 octeon_i2c_xfer的代码：
static int octeon_i2c_xfer(struct i2c_adapter *adap,
struct i2c_msg *msgs,
int num)
{
printk(KERN_DEBUG "here is octeon_i2c_xfer,num = %dn",num);
struct i2c_msg *pmsg;
int i;
int ret = 0;
struct octeon_i2c *i2c = i2c_get_adapdata(adap);
if (num == 1) {
if (msgs[0].len > 0 && msgs[0].len <= 8) {
if (msgs[0].flags & I2C_M_RD)
ret = octeon_i2c_simple_read(i2c, msgs);
else
ret = octeon_i2c_simple_write(i2c, msgs);
goto out;
}
} else if (num == 2) {
if ((msgs[0].flags & I2C_M_RD) == 0 &&
msgs[0].len > 0 && msgs[0].len <= 2 &&
msgs[1].len > 0 && msgs[1].len <= 8 &&
msgs[0].addr == msgs[1].addr) {
if (msgs[1].flags & I2C_M_RD)
ret = octeon_i2c_ia_read(i2c, msgs);
else
ret = octeon_i2c_ia_write(i2c, msgs);
goto out;
}
}
for (i = 0; ret == 0 && i < num; i++) {
pmsg = &msgs[i];
dev_dbg(i2c->dev,
"Doing %s %d byte(s) to/from 0x%02x - %d of %d messagesn",
pmsg->flags & I2C_M_RD ? "read" : "write",
pmsg->len, pmsg->addr, i + 1, num);
if (pmsg->flags & I2C_M_RD)
ret = octeon_i2c_read(i2c, pmsg->addr, pmsg->buf,
pmsg->len, i);
}
octeon_i2c_stop(i2c);
out:
return (ret != 0) ? ret : num;
}
通过在 i2c-core.c： i2c_master_send（）中添加printk，
//added by handwei.2012.7.5
printk(KERN_DEBUG "%s: msg.addr = %x,msg.flags = %x,msg.len = %d,msg.buf(data) =
%sn",__func__,msg.addr,msg.flags,msg.len,msg.buf);
运行后可以看到 msg.flags 一直等于0 ，那么 在 octeon_i2c_xfer （）中
if (num == 1) {
if (msgs[0].len > 0 && msgs[0].len <= 8) {
if (msgs[0].flags & I2C_M_RD)
ret = octeon_i2c_simple_read(i2c, msgs);
else
ret = octeon_i2c_simple_write(i2c, msgs);
goto out;
会一直进入octeon_i2c_simple_write()执行写操作。 下面是octeon_i2c_simple_write()的代码：
static int octeon_i2c_simple_write(struct octeon_i2c *i2c, struct i2c_msg *msgs)
{
u64 cmd;
int i, j;
int ret = 0;
octeon_i2c_enable_hlc(i2c);
printk(KERN_DEBUG "%s:n",__func__);
retry:
cmd = SW_TWSI_V | SW_TWSI_SOVR;
/* SIZE */
cmd |= (u64)(msgs[0].len - 1) << SW_TWSI_SIZE_SHIFT;
/* A */
cmd |= (u64)(msgs[0].addr & 0x7full) << SW_TWSI_A_SHIFT;
if (msgs[0].flags & I2C_M_TEN)
cmd |= SW_TWSI_OP_10;
else
cmd |= SW_TWSI_OP_7;
printk(KERN_DEBUG "%s:cmd = %llxn",__func__,cmd);
for (i = 0, j = msgs[0].len - 1; i < msgs[0].len && i < 4; i++, j--){
cmd |= (u64)msgs[0].buf[j] << (8 * i);
printk(KERN_DEBUG "%s:msgs[0].buf[%d] = %x,cmd = %llxn",__func__,j,msgs[0].buf
[j],cmd);
}
if (msgs[0].len >= 4) {
u64 ext = 0;
for (i = 0; i < msgs[0].len - 4 && i < 4; i++, j--)
ext |= (u64)msgs[0].buf[j] << (8 * i);
printk(KERN_DEBUG "%s:ext = %llxn",__func__,ext);
__raw_writeq(ext, i2c->twsi_base + SW_TWSI_EXT);
}
octeon_i2c_hlc_int_clear(i2c);
__raw_writeq(cmd, i2c->twsi_base + SW_TWSI);
ret = octeon_i2c_hlc_wait(i2c);
if (ret)
goto err;
cmd = __raw_readq(i2c->twsi_base + SW_TWSI);
if ((cmd & SW_TWSI_R) == 0) {
if (octeon_i2c_lost_arb(cmd))
goto retry;
ret = -EIO;
goto err;
}
err:
return ret;
}
下面是版卡执行 hwclock -w 后的dmesg 中的一部分：
[ 38.989069] pcf8563_get_datetime: secs=4, mins=41, hours=18,ecs=5, mins=6, hours=11
2
[ 40.292306] pcf8563_set_datetime: secs=5, mins=41, hours=18,ecs=5, mins=6, hours=112
[ 40.292321] pcf8563_set_datetime:data[0] = 2,data[1] = 5
[ 40.292333] i2c_master_send: msg.addr = 51,msg.flags = 0,msg.len = 2,msg.buf[0] = 2,msg.
buf[1] = 5
[ 40.292346] here is octeon_i2c_xfer, num = 1
[ 40.292355] octeon_i2c_simple_write:
[ 40.292363] octeon_i2c_simple_write:cmd = 8090510000000000
[ 40.292374] octeon_i2c_simple_write:msgs[0].buf[1] = 5,cmd = 8090510000000005
[ 40.292386] octeon_i2c_simple_write:msgs[0].buf[0] = 2,cmd = 8090510000000205
[ 40.292687] pcf8563_set_datetime:data[0] = 3,data[1] = 41
[ 40.292699] i2c_master_send: msg.addr = 51,msg.flags = 0,msg.len = 2,msg.buf[0] = 3,msg.
buf[1] = 41
[ 40.292712] here is octeon_i2c_xfer, num = 1
[ 40.292719] octeon_i2c_simple_write:
[ 40.292727] octeon_i2c_simple_write:cmd = 8090510000000000
[ 40.292738] octeon_i2c_simple_write:msgs[0].buf[1] = 41,cmd = 8090510000000041
[ 40.292750] octeon_i2c_simple_write:msgs[0].buf[0] = 3,cmd = 8090510000000341
[ 40.293049] pcf8563_set_datetime:data[0] = 4,data[1] = 18
[ 40.293061] i2c_master_send: msg.addr = 51,msg.flags = 0,msg.len = 2,msg.buf[0] = 4,msg.
buf[1] = 18
[ 40.293074] here is octeon_i2c_xfer, num = 1
[ 40.293082] octeon_i2c_simple_write:
[ 40.293089] octeon_i2c_simple_write:cmd = 8090510000000000
[ 40.293100] octeon_i2c_simple_write:msgs[0].buf[1] = 18,cmd = 8090510000000018
[ 40.293112] octeon_i2c_simple_write:msgs[0].buf[0] = 4,cmd = 8090510000000418
[ 40.293411] pcf8563_set_datetime:data[0] = 5,data[1] = 5
[ 40.293423] i2c_master_send: msg.addr = 51,msg.flags = 0,msg.len = 2,msg.buf[0] = 5,msg.
buf[1] = 5
[ 40.293435] here is octeon_i2c_xfer, num = 1
[ 40.293443] octeon_i2c_simple_write:
[ 40.293451] octeon_i2c_simple_write:cmd = 8090510000000000
[ 40.293462] octeon_i2c_simple_write:msgs[0].buf[1] = 5,cmd = 8090510000000005
[ 40.293474] octeon_i2c_simple_write:msgs[0].buf[0] = 5,cmd = 8090510000000505
[ 40.293772] pcf8563_set_datetime:data[0] = 6,data[1] = 4
[ 40.293784] i2c_master_send: msg.addr = 51,msg.flags = 0,msg.len = 2,msg.buf[0] = 6,msg.
buf[1] = 4
[ 40.293796] here is octeon_i2c_xfer, num = 1
[ 40.293804] octeon_i2c_simple_write:
[ 40.293812] octeon_i2c_simple_write:cmd = 8090510000000000
[ 40.293822] octeon_i2c_simple_write:msgs[0].buf[1] = 4,cmd = 8090510000000004
[ 40.293835] octeon_i2c_simple_write:msgs[0].buf[0] = 6,cmd = 8090510000000604
[ 40.294133] pcf8563_set_datetime:data[0] = 7,data[1] = 7
[ 40.294145] i2c_master_send: msg.addr = 51,msg.flags = 0,msg.len = 2,msg.buf[0] = 7,msg.
buf[1] = 7
[ 40.294157] here is octeon_i2c_xfer, num = 1
[ 40.294165] octeon_i2c_simple_write:
[ 40.294173] octeon_i2c_simple_write:cmd = 8090510000000000
[ 40.294184] octeon_i2c_simple_write:msgs[0].buf[1] = 7,cmd = 8090510000000007
[ 40.294196] octeon_i2c_simple_write:msgs[0].buf[0] = 7,cmd = 8090510000000707
[ 40.294494] pcf8563_set_datetime:data[0] = 8,data[1] = 12
[ 40.294506] i2c_master_send: msg.addr = 51,msg.flags = 0,msg.len = 2,msg.buf[0] = 8,msg.
buf[1] = 12
[ 40.294519] here is octeon_i2c_xfer, num = 1
[ 40.294526] octeon_i2c_simple_write:
[ 40.294534] octeon_i2c_simple_write:cmd = 8090510000000000
[ 40.294545] octeon_i2c_simple_write:msgs[0].buf[1] = 12,cmd = 8090510000000012
[ 40.294557] octeon_i2c_simple_write:msgs[0].buf[0] = 8,cmd = 8090510000000812
pcf8563_get_datetime: 是读到的时间
pcf8563_set_datetime: 是要写的时间
在第一个部分：
[ 40.292321] pcf8563_set_datetime:data[0] = 2,data[1] = 5
[ 40.292333] i2c_master_send: msg.addr = 51,msg.flags = 0,msg.len = 2,msg.buf[0] = 2,msg.
buf[1] = 5
[ 40.292346] here is octeon_i2c_xfer, num = 1
[ 40.292355] octeon_i2c_simple_write:
[ 40.292363] octeon_i2c_simple_write:cmd = 8090510000000000
[ 40.292374] octeon_i2c_simple_write:msgs[0].buf[1] = 5,cmd = 8090510000000005
[ 40.292386] octeon_i2c_simple_write:msgs[0].buf[0] = 2,cmd = 8090510000000205
在pcf8563_set_datetime （）中：
for (i = 0; i < 7; i++) {
unsigned char data[2] = { PCF8563_REG_SC + i,
//注意： #define PCF8563_REG_SC 0x02
err = i2c_master_send(client, data, sizeof(data));
if (err != sizeof(data)) {
dev_err(&client->dev,
"%s: err=%d addr=%02x, data=%02xn",
__func__, err, data[0], data[1]);
}
通过i2c_master_send()进入octeon_i2c_xfer（），再进入 octeon_i2c_simple_write，
{
cmd = SW_TWSI_V | SW_TWSI_SOVR;
cmd |= (u64)(msgs[0].len - 1) << SW_TWSI_SIZE_SHIFT;
// Address field.：<49:40>
cmd |= (u64)(msgs[0].addr & 0x7full) << SW_TWSI_A_SHIFT;
if (msgs[0].flags & I2C_M_TEN)
cmd |= SW_TWSI_OP_10;
for (i = 0, j = msgs[0].len - 1; i < msgs[0].len && i < 4; i++, j--){
cmd |= (u64)msgs[0].buf[j] << (8 * i);
...
}
根据msgs中的len，addr，flags, buf[]中的内容填充cmd，执行cmd 并 返回执行结果
同样的， 在进入第二次循环时， 这时操作的是pcf8563 的第三个寄存器，03h： minutes 分钟寄存器。
[ 40.292687] pcf8563_set_datetime:data[0] = 3,data[1] = 41
[ 40.292699] i2c_master_send: msg.addr = 51,msg.flags = 0,msg.len = 2,msg.buf[0] = 3,msg.
buf[1] = 41
[ 40.292712] here is octeon_i2c_xfer, num = 1
[ 40.292719] octeon_i2c_simple_write:
[ 40.292727] octeon_i2c_simple_write:cmd = 8090510000000000
[ 40.292738] octeon_i2c_simple_write:msgs[0].buf[1] = 41,cmd = 8090510000000041
[ 40.292750] octeon_i2c_simple_write:msgs[0].buf[0] = 3,cmd = 8090510000000341
第三次，操作pcf8563的第四个寄存器：04h hours
[ 40.293049] pcf8563_set_datetime:data[0] = 4,data[1] = 18
[ 40.293061] i2c_master_send: msg.addr = 51,msg.flags = 0,msg.len = 2,msg.buf[0] = 4,msg.
buf[1] = 18
[ 40.293074] here is octeon_i2c_xfer, num = 1
[ 40.293082] octeon_i2c_simple_write:
[ 40.293089] octeon_i2c_simple_write:cmd = 8090510000000000
[ 40.293100] octeon_i2c_simple_write:msgs[0].buf[1] = 18,cmd = 8090510000000018
[ 40.293112] octeon_i2c_simple_write:msgs[0].buf[0] = 4,cmd = 8090510000000418
我们看到：
hwclock -w 通过 octeon_i2c_simple_write 来写pcf8563时钟芯片，
其中：msg.addr = 0x51 , msg.len = 2 ,msg.flags = 0,
msg.buf[0] = 相应地址偏移
msg.buf[1] = 给相应寄存器的值
那么我们的i2c-test, 也这样操作试试：
包装一个msg, 传入octeon_i2c_xfer（），再传入 octeon_i2c_simple_write，看看能不能得到期望的执
行结果。
另外 ， 还要通过hwclock 来观察 ，为什么没有使用octeon_i2c_simple_read 来读寄存器的现象。
注意到：
在关于写的操作中： pcf8563_set_datetime（）
i2c_master_send（）
{.
.
msg.addr = client->addr;
msg.flags = client->flags & I2C_M_TEN;
msg.len = count;
msg.buf = (char *)buf;
ret = i2c_transfer(adap, &msg, 1);
..}