static int __init i2c_gpio_init(void)
{
int ret;
ret = platform_driver_register(&i2c_gpio_driver);
if (ret)
printk(KERN_ERR "i2c-gpio: probe failed: %d\n", ret);
return ret;
}
subsys_initcall(i2c_gpio_init);
static void __exit i2c_gpio_exit(void)
{
platform_driver_unregister(&i2c_gpio_driver);
}
module_exit(i2c_gpio_exit);
#if defined(CONFIG_OF)
static const struct of_device_id i2c_gpio_dt_ids[] = {
{ .compatible = "i2c-gpio", },
{ /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, i2c_gpio_dt_ids);
#endif
static struct platform_driver i2c_gpio_driver = {
.driver = {
.name = "i2c-gpio",
.of_match_table = of_match_ptr(i2c_gpio_dt_ids),
},
.probe = i2c_gpio_probe,
.remove = i2c_gpio_remove,
};
/*
* i2c_adapter is the structure used to identify a physical i2c bus along
* with the access algorithms necessary to access it.
*/
struct i2c_adapter {
struct module *owner;
unsigned int class; /* classes to allow probing for */
const struct i2c_algorithm *algo; /* the algorithm to access the bus */
void *algo_data;
/* data fields that are valid for all devices */
const struct i2c_lock_operations *lock_ops;
struct rt_mutex bus_lock;
struct rt_mutex mux_lock;
int timeout; /* in jiffies */
int retries;
struct device dev; /* the adapter device */
int nr;
char name[48];
struct completion dev_released;
struct mutex userspace_clients_lock;
struct list_head userspace_clients;
struct i2c_bus_recovery_info *bus_recovery_info;
const struct i2c_adapter_quirks *quirks;
};
/* --- Defines for bit-adapters --------------------------------------- */
/*
* This struct contains the hw-dependent functions of bit-style adapters to
* manipulate the line states, and to init any hw-specific features. This is
* only used if you have more than one hw-type of adapter running.
*/
struct i2c_algo_bit_data {
void *data; /* private data for lowlevel routines */
void (*setsda) (void *data, int state);
void (*setscl) (void *data, int state);
int (*getsda) (void *data);
int (*getscl) (void *data);
int (*pre_xfer) (struct i2c_adapter *);
void (*post_xfer) (struct i2c_adapter *);
/* local settings */
int udelay; /* half clock cycle time in us,
minimum 2 us for fast-mode I2C,
minimum 5 us for standard-mode I2C and SMBus,
maximum 50 us for SMBus */
int timeout; /* in jiffies */
};
/**
* struct i2c_gpio_platform_data - Platform-dependent data for i2c-gpio
* @sda_pin: GPIO pin ID to use for SDA
* @scl_pin: GPIO pin ID to use for SCL
* @udelay: signal toggle delay. SCL frequency is (500 / udelay) kHz
* @timeout: clock stretching timeout in jiffies. If the slave keeps
* SCL low for longer than this, the transfer will time out.
* @sda_is_open_drain: SDA is configured as open drain, i.e. the pin
* isn't actively driven high when setting the output value high.
* gpio_get_value() must return the actual pin state even if the
* pin is configured as an output.
* @scl_is_open_drain: SCL is set up as open drain. Same requirements
* as for sda_is_open_drain apply.
* @scl_is_output_only: SCL output drivers cannot be turned off.
*/
struct i2c_gpio_platform_data {
unsigned int sda_pin;
unsigned int scl_pin;
int udelay;
int timeout;
unsigned int sda_is_open_drain:1;
unsigned int scl_is_open_drain:1;
unsigned int scl_is_output_only:1;
};
struct i2c_gpio_private_data {
struct i2c_adapter adap;
struct i2c_algo_bit_data bit_data;
struct i2c_gpio_platform_data pdata;
};
static int i2c_gpio_probe(struct platform_device *pdev)
{
struct i2c_gpio_private_data *priv;
struct i2c_gpio_platform_data *pdata;
struct i2c_algo_bit_data *bit_data;
struct i2c_adapter *adap;
unsigned int sda_pin, scl_pin;
int ret;
/* First get the GPIO pins; if it fails, we'll defer the probe. */
if (pdev->dev.of_node) {
ret = of_i2c_gpio_get_pins(pdev->dev.of_node,
&sda_pin, &scl_pin);
if (ret)
return ret;
} else {
if (!dev_get_platdata(&pdev->dev))
return -ENXIO;
pdata = dev_get_platdata(&pdev->dev);
sda_pin = pdata->sda_pin;
scl_pin = pdata->scl_pin;
}
ret = devm_gpio_request(&pdev->dev, sda_pin, "sda");
if (ret) {
if (ret == -EINVAL)
ret = -EPROBE_DEFER; /* Try again later */
return ret;
}
ret = devm_gpio_request(&pdev->dev, scl_pin, "scl");
if (ret) {
if (ret == -EINVAL)
ret = -EPROBE_DEFER; /* Try again later */
return ret;
}
priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
if (!priv)
return -ENOMEM;
adap = &priv->adap;
bit_data = &priv->bit_data;
pdata = &priv->pdata;
if (pdev->dev.of_node) {
pdata->sda_pin = sda_pin;
pdata->scl_pin = scl_pin;
of_i2c_gpio_get_props(pdev->dev.of_node, pdata);
} else {
memcpy(pdata, dev_get_platdata(&pdev->dev), sizeof(*pdata));
}
if (pdata->sda_is_open_drain) {
gpio_direction_output(pdata->sda_pin, 1);
bit_data->setsda = i2c_gpio_setsda_val;
} else {
gpio_direction_input(pdata->sda_pin);
bit_data->setsda = i2c_gpio_setsda_dir;
}
if (pdata->scl_is_open_drain || pdata->scl_is_output_only) {
gpio_direction_output(pdata->scl_pin, 1);
bit_data->setscl = i2c_gpio_setscl_val;
} else {
gpio_direction_input(pdata->scl_pin);
bit_data->setscl = i2c_gpio_setscl_dir;
}
if (!pdata->scl_is_output_only)
bit_data->getscl = i2c_gpio_getscl;
bit_data->getsda = i2c_gpio_getsda;
if (pdata->udelay)
bit_data->udelay = pdata->udelay;
else if (pdata->scl_is_output_only)
bit_data->udelay = 50; /* 10 kHz */
else
bit_data->udelay = 5; /* 100 kHz */
if (pdata->timeout)
bit_data->timeout = pdata->timeout;
else
bit_data->timeout = HZ / 10; /* 100 ms */
bit_data->data = pdata;
adap->owner = THIS_MODULE;
if (pdev->dev.of_node)
strlcpy(adap->name, dev_name(&pdev->dev), sizeof(adap->name));
else
snprintf(adap->name, sizeof(adap->name), "i2c-gpio%d", pdev->id);
adap->algo_data = bit_data;
adap->class = I2C_CLASS_HWMON | I2C_CLASS_SPD;
adap->dev.parent = &pdev->dev;
adap->dev.of_node = pdev->dev.of_node;
adap->nr = pdev->id;
ret = i2c_bit_add_numbered_bus(adap);
if (ret)
return ret;
platform_set_drvdata(pdev, priv);
dev_info(&pdev->dev, "using pins %u (SDA) and %u (SCL%s)\n",
pdata->sda_pin, pdata->scl_pin,
pdata->scl_is_output_only
? ", no clock stretching" : "");
return 0;
}
static int i2c_gpio_remove(struct platform_device *pdev)
{
struct i2c_gpio_private_data *priv;
struct i2c_adapter *adap;
priv = platform_get_drvdata(pdev);
adap = &priv->adap;
i2c_del_adapter(adap);
return 0;
}
int i2c_bit_add_numbered_bus(struct i2c_adapter *adap)
{
return __i2c_bit_add_bus(adap, i2c_add_numbered_adapter);
}
EXPORT_SYMBOL(i2c_bit_add_numbered_bus);
/*
* registering functions to load algorithms at runtime
*/
static int __i2c_bit_add_bus(struct i2c_adapter *adap,
int (*add_adapter)(struct i2c_adapter *))
{
struct i2c_algo_bit_data *bit_adap = adap->algo_data;
int ret;
if (bit_test) {
ret = test_bus(adap);
if (bit_test >= 2 && ret < 0)
return -ENODEV;
}
/* register new adapter to i2c module... */
adap->algo = &i2c_bit_algo;
adap->retries = 3;
if (bit_adap->getscl == NULL)
adap->quirks = &i2c_bit_quirk_no_clk_stretch;
ret = add_adapter(adap);
if (ret < 0)
return ret;
/* Complain if SCL can't be read */
if (bit_adap->getscl == NULL) {
dev_warn(&adap->dev, "Not I2C compliant: can't read SCL\n");
dev_warn(&adap->dev, "Bus may be unreliable\n");
}
return 0;
}
/* -----exported algorithm data: ------------------------------------- */
const struct i2c_algorithm i2c_bit_algo = {
.master_xfer = bit_xfer,
.functionality = bit_func,
};
EXPORT_SYMBOL(i2c_bit_algo);
/*
* Sanity check for the adapter hardware - check the reaction of
* the bus lines only if it seems to be idle.
*/
static int test_bus(struct i2c_adapter *i2c_adap)
{
struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
const char *name = i2c_adap->name;
int scl, sda, ret;
if (adap->pre_xfer) {
ret = adap->pre_xfer(i2c_adap);
if (ret < 0)
return -ENODEV;
}
if (adap->getscl == NULL)
pr_info("%s: Testing SDA only, SCL is not readable\n", name);
sda = getsda(adap);
scl = (adap->getscl == NULL) ? 1 : getscl(adap);
if (!scl || !sda) {
printk(KERN_WARNING
"%s: bus seems to be busy (scl=%d, sda=%d)\n",
name, scl, sda);
goto bailout;
}
sdalo(adap);
sda = getsda(adap);
scl = (adap->getscl == NULL) ? 1 : getscl(adap);
if (sda) {
printk(KERN_WARNING "%s: SDA stuck high!\n", name);
goto bailout;
}
if (!scl) {
printk(KERN_WARNING "%s: SCL unexpected low "
"while pulling SDA low!\n", name);
goto bailout;
}
sdahi(adap);
sda = getsda(adap);
scl = (adap->getscl == NULL) ? 1 : getscl(adap);
if (!sda) {
printk(KERN_WARNING "%s: SDA stuck low!\n", name);
goto bailout;
}
if (!scl) {
printk(KERN_WARNING "%s: SCL unexpected low "
"while pulling SDA high!\n", name);
goto bailout;
}
scllo(adap);
sda = getsda(adap);
scl = (adap->getscl == NULL) ? 0 : getscl(adap);
if (scl) {
printk(KERN_WARNING "%s: SCL stuck high!\n", name);
goto bailout;
}
if (!sda) {
printk(KERN_WARNING "%s: SDA unexpected low "
"while pulling SCL low!\n", name);
goto bailout;
}
sclhi(adap);
sda = getsda(adap);
scl = (adap->getscl == NULL) ? 1 : getscl(adap);
if (!scl) {
printk(KERN_WARNING "%s: SCL stuck low!\n", name);
goto bailout;
}
if (!sda) {
printk(KERN_WARNING "%s: SDA unexpected low "
"while pulling SCL high!\n", name);
goto bailout;
}
if (adap->post_xfer)
adap->post_xfer(i2c_adap);
pr_info("%s: Test OK\n", name);
return 0;
bailout:
sdahi(adap);
sclhi(adap);
if (adap->post_xfer)
adap->post_xfer(i2c_adap);
return -ENODEV;
}
This routine is used to declare an I2C adapter when its bus number matters. For example, use it for I2C adapters from system-on-chip CPUs, or otherwise built in to the system’s mainboard, and where i2c_board_info is used to properly configure I2C devices. If the requested bus number is set to -1, then this function will behave identically to i2c_add_adapter, and will dynamically assign a bus number. If no devices have pre-been declared for this bus, then be sure to register the adapter before any dynamically allocated ones. Otherwise the required bus ID may not be available. When this returns zero, the specified adapter became available for clients using the bus number provided in adap->nr. Also, the table of I2C devices pre-declared using i2c_register_board_info() is scanned, and the appropriate driver model device nodes are created. Otherwise, a negative errno value is returned.
本例程用于通过指定的总线号声明I2C适配器，当传入的总线号为-1时，此函数的行为将与i2c_add_adapter函数一致，并且给适配器动态分配一个总线号；
如果尚未为总线分配任何设备，则必须保证设备在动态分配之前，先注册适配器，否则可能无法使用指定的总线号；
指定的适配器可以使用adap->nr中提供的总线号供clients使用，使用i2c_register_board_info()函数预声明的I2C设备表将会被扫描并且分配合适的设备驱动节点，若执行成功则最终返回0，如果上述执行不成功，返回errno；
i2c_add_numbered_adapter函数代码清单：
int i2c_add_numbered_adapter(struct i2c_adapter *adap)
{
if (adap->nr == -1) /* -1 means dynamically assign bus id */
return i2c_add_adapter(adap);
return __i2c_add_numbered_adapter(adap);
}
EXPORT_SYMBOL_GPL(i2c_add_numbered_adapter);
i2c_add_adapter函数代码：
int i2c_add_adapter(struct i2c_adapter *adapter)
{
struct device *dev = &adapter->dev;
int id;
if (dev->of_node) { /* check if the dev_node is previously allocated. */
id = of_alias_get_id(dev->of_node, "i2c");
if (id >= 0) {
adapter->nr = id;
return __i2c_add_numbered_adapter(adapter);
}
}
mutex_lock(&core_lock); /* no device in assigned bus, alloc for the adapter firstly */
id = idr_alloc(&i2c_adapter_idr, adapter,
__i2c_first_dynamic_bus_num, 0, GFP_KERNEL);
mutex_unlock(&core_lock);
if (WARN(id < 0, "couldn't get idr"))
return id;
adapter->nr = id;
return i2c_register_adapter(adapter);
}
EXPORT_SYMBOL(i2c_add_adapter);
__i2c_add_numbered_adapter函数代码：
static int __i2c_add_numbered_adapter(struct i2c_adapter *adap)
{
int id;
mutex_lock(&core_lock);
id = idr_alloc(&i2c_adapter_idr, adap, adap->nr, adap->nr + 1, GFP_KERNEL);
mutex_unlock(&core_lock);
if (WARN(id < 0, "couldn't get idr"))
return id == -ENOSPC ? -EBUSY : id;
return i2c_register_adapter(adap);
}
i2c_register_adapter函数代码：
static int i2c_register_adapter(struct i2c_adapter *adap)
{
int res = -EINVAL;
/* Can't register until after driver model init */
if (WARN_ON(!is_registered)) {
res = -EAGAIN;
goto out_list;
}
/* Sanity checks */
if (WARN(!adap->name[0], "i2c adapter has no name"))
goto out_list;
if (!adap->algo) {
pr_err("adapter '%s': no algo supplied!\n", adap->name);
goto out_list;
}
if (!adap->lock_ops)
adap->lock_ops = &i2c_adapter_lock_ops;
rt_mutex_init(&adap->bus_lock);
rt_mutex_init(&adap->mux_lock);
mutex_init(&adap->userspace_clients_lock);
INIT_LIST_HEAD(&adap->userspace_clients);
/* Set default timeout to 1 second if not already set */
if (adap->timeout == 0)
adap->timeout = HZ;
dev_set_name(&adap->dev, "i2c-%d", adap->nr);
adap->dev.bus = &i2c_bus_type;
adap->dev.type = &i2c_adapter_type;
res = device_register(&adap->dev);
if (res) {
pr_err("adapter '%s': can't register device (%d)\n", adap->name, res);
goto out_list;
}
dev_dbg(&adap->dev, "adapter [%s] registered\n", adap->name);
pm_runtime_no_callbacks(&adap->dev);
pm_suspend_ignore_children(&adap->dev, true);
pm_runtime_enable(&adap->dev);
#ifdef CONFIG_I2C_COMPAT
res = class_compat_create_link(i2c_adapter_compat_class, &adap->dev,
adap->dev.parent);
if (res)
dev_warn(&adap->dev,
"Failed to create compatibility class link\n");
#endif
i2c_init_recovery(adap); /* reinit SCL gpio value function */
/* create pre-declared device nodes */
of_i2c_register_devices(adap);
i2c_acpi_register_devices(adap);
i2c_acpi_install_space_handler(adap);
if (adap->nr < __i2c_first_dynamic_bus_num)
i2c_scan_static_board_info(adap);
/* Notify drivers */
mutex_lock(&core_lock);
bus_for_each_drv(&i2c_bus_type, NULL, adap, __process_new_adapter);
mutex_unlock(&core_lock);
return 0;
out_list:
mutex_lock(&core_lock);
idr_remove(&i2c_adapter_idr, adap->nr);
mutex_unlock(&core_lock);
return res;
}
static int bit_xfer(struct i2c_adapter *i2c_adap,
struct i2c_msg msgs[], int num)
{
struct i2c_msg *pmsg;
struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
int i, ret;
unsigned short nak_ok;
if (adap->pre_xfer) {
ret = adap->pre_xfer(i2c_adap);
if (ret < 0)
return ret;
}
bit_dbg(3, &i2c_adap->dev, "emitting start condition\n");
i2c_start(adap);
for (i = 0; i < num; i++) {
pmsg = &msgs[i];
nak_ok = pmsg->flags & I2C_M_IGNORE_NAK; /* 忽略应答信号标志 */
if (!(pmsg->flags & I2C_M_NOSTART)) { /* 无起始信号标志 */
if (i) {
bit_dbg(3, &i2c_adap->dev, "emitting "
"repeated start condition\n");
i2c_repstart(adap);
}
ret = bit_doAddress(i2c_adap, pmsg);
if ((ret != 0) && !nak_ok) {
bit_dbg(1, &i2c_adap->dev, "NAK from "
"device addr 0x%02x msg #%d\n",
msgs[i].addr, i);
goto bailout;
}
}
if (pmsg->flags & I2C_M_RD) { /* 读标志 */
/* read bytes into buffer*/
ret = readbytes(i2c_adap, pmsg);
if (ret >= 1)
bit_dbg(2, &i2c_adap->dev, "read %d byte%s\n",
ret, ret == 1 ? "" : "s");
if (ret < pmsg->len) {
if (ret >= 0)
ret = -EIO;
goto bailout;
}
} else { /* 写标志 */
/* write bytes from buffer */
ret = sendbytes(i2c_adap, pmsg);
if (ret >= 1)
bit_dbg(2, &i2c_adap->dev, "wrote %d byte%s\n",
ret, ret == 1 ? "" : "s");
if (ret < pmsg->len) {
if (ret >= 0)
ret = -EIO;
goto bailout;
}
}
}
ret = i;
bailout:
bit_dbg(3, &i2c_adap->dev, "emitting stop condition\n");
i2c_stop(adap);
if (adap->post_xfer)
adap->post_xfer(i2c_adap);
return ret;
}
在 I2C 总线中，唯一出现的是被定义为起始 S 和停止P 条件的情况，其中一种情况是在 SCL 线是高电平时，SDA 线从高电平向低电平切换 这个情况表示起始条件；当 SCL 是高电平时，SDA 线由低电平向高电平切换表示停止条件。起始和停止条件一般由主机产生，总线在起始条件后被认为处于忙的状态，在停止条件的某段时间后，总线被认为再次处于空闲状态。
具体的函数代码实现如下：
static inline void sdalo(struct i2c_algo_bit_data *adap)
{
setsda(adap, 0);
udelay((adap->udelay + 1) / 2);
}
static inline void sdahi(struct i2c_algo_bit_data *adap)
{
setsda(adap, 1);
udelay((adap->udelay + 1) / 2);
}
static inline void scllo(struct i2c_algo_bit_data *adap)
{
setscl(adap, 0);
udelay(adap->udelay / 2);
}
/*
* Raise scl line, and do checking for delays. This is necessary for slower
* devices.
*/
static int sclhi(struct i2c_algo_bit_data *adap)
{
unsigned long start;
setscl(adap, 1);
/* Not all adapters have scl sense line... */
if (!adap->getscl)
goto done;
start = jiffies;
while (!getscl(adap)) {
/* This hw knows how to read the clock line, so we wait
* until it actually gets high. This is safer as some
* chips may hold it low ("clock stretching") while they
* are processing data internally.
*/
/*
* 该硬件知道如何读取时钟线，因此我们等到它实际变高。
* 这样比较安全，因为某些芯片在内部处理数据时可能会
* 将其保持在低电平（“时钟延长”）
*/
if (time_after(jiffies, start + adap->timeout)) {
/* Test one last time, as we may have been preempted
* between last check and timeout test.
*/
if (getscl(adap))
break;
return -ETIMEDOUT;
}
cpu_relax();
}
#ifdef DEBUG
if (jiffies != start && i2c_debug >= 3)
pr_debug("i2c-algo-bit: needed %ld jiffies for SCL to go "
"high\n", jiffies - start);
#endif
done:
udelay(adap->udelay);
return 0;
}
/* --- other auxiliary functions -------------------------------------- */
static void i2c_start(struct i2c_algo_bit_data *adap)
{
/* assert: scl, sda are high */
setsda(adap, 0); /* set sda to low level */
udelay(adap->udelay); /* wait for slave to acknowledge */
scllo(adap); /* set scl to low level and delay */
}
static void i2c_stop(struct i2c_algo_bit_data *adap)
{
/* assert: scl is low */
sdalo(adap); /* set sda to low level and delay */
sclhi(adap); /* set scl to high level and delay */
setsda(adap, 1); /* set sda to high level */
udelay(adap->udelay); /* wait for slave to acknowledge */
}
相关宏定义及其含义：
I2C_M_TEN表示10位设备地址
I2C_M_RD读标志
I2C_M_NOSTART无起始信号标志
I2C_M_IGNORE_NAK忽略应答信号标志
首先解析是否对ack应答、以及是否为重复开始标志；
通过解析寻址规则，查找从i2c设备，具体函数实现如doAddress，它通过生成开始条件（在try_address中）来启动传输（将地址字节发送出去），并以必要的格式传输地址以处理读取和写入字节（8位及10位地址）。返回值：0正常，从设备发送ack，或设置了IGNORE_NAK标志-x发生错误（例如：-ENXIO，设备未应答，或-ETIMEDOUT，例如，线路阻塞）：
/* doAddress initiates the transfer by generating the start condition (in
* try_address) and transmits the address in the necessary format to handle
* reads, writes as well as 10bit-addresses.
* returns:
* 0 everything went okay, the chip ack'ed, or IGNORE_NAK flag was set
* -x an error occurred (like: -ENXIO if the device did not answer, or
* -ETIMEDOUT, for example if the lines are stuck...)
*/
static int bit_doAddress(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
{
unsigned short flags = msg->flags;
unsigned short nak_ok = msg->flags & I2C_M_IGNORE_NAK;
struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
unsigned char addr;
int ret, retries;
retries = nak_ok ? 0 : i2c_adap->retries;
if (flags & I2C_M_TEN) {
/* a ten bit address */
addr = 0xf0 | ((msg->addr >> 7) & 0x06);
bit_dbg(2, &i2c_adap->dev, "addr0: %d\n", addr);
/* try extended address code...*/
ret = try_address(i2c_adap, addr, retries);
if ((ret != 1) && !nak_ok) {
dev_err(&i2c_adap->dev,
"died at extended address code\n");
return -ENXIO;
}
/* the remaining 8 bit address */
ret = i2c_outb(i2c_adap, msg->addr & 0xff);
if ((ret != 1) && !nak_ok) {
/* the chip did not ack / xmission error occurred */
dev_err(&i2c_adap->dev, "died at 2nd address code\n");
return -ENXIO;
}
if (flags & I2C_M_RD) {
bit_dbg(3, &i2c_adap->dev, "emitting repeated "
"start condition\n");
i2c_repstart(adap);
/* okay, now switch into reading mode */
addr |= 0x01;
ret = try_address(i2c_adap, addr, retries);
if ((ret != 1) && !nak_ok) {
dev_err(&i2c_adap->dev,
"died at repeated address code\n");
return -EIO;
}
}
} else { /* normal 7bit address */
addr = msg->addr << 1;
if (flags & I2C_M_RD)
addr |= 1;
if (flags & I2C_M_REV_DIR_ADDR)
addr ^= 1;
ret = try_address(i2c_adap, addr, retries);
if ((ret != 1) && !nak_ok)
return -ENXIO;
}
return 0;
}
tryAddress函数向芯片发送一个地址字节，用于匹配i2c从机，retries代表它的失败重试次数：
/* try_address tries to contact a chip for a number of
* times before it gives up.
* return values:
* 1 chip answered
* 0 chip did not answer
* -x transmission error
*/
static int try_address(struct i2c_adapter *i2c_adap,
unsigned char addr, int retries)
{
struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
int i, ret = 0;
for (i = 0; i <= retries; i++) {
ret = i2c_outb(i2c_adap, addr);
if (ret == 1 || i == retries)
break;
bit_dbg(3, &i2c_adap->dev, "emitting stop condition\n");
i2c_stop(adap);
udelay(adap->udelay);
yield();
bit_dbg(3, &i2c_adap->dev, "emitting start condition\n");
i2c_start(adap);
}
if (i && ret)
bit_dbg(1, &i2c_adap->dev, "Used %d tries to %s client at "
"0x%02x: %s\n", i + 1,
addr & 1 ? "read from" : "write to", addr >> 1,
ret == 1 ? "success" : "failed, timeout?");
return ret;
}
i2c_outb函数是实现tryAddress函数进行地址字节发送的关键，它将一个字节进行发送，并对ack进行检查，具体实现如下：
/* send a byte without start cond., look for arbitration,
check ackn. from slave */
/* returns:
* 1 if the device acknowledged
* 0 if the device did not ack
* -ETIMEDOUT if an error occurred (while raising the scl line)
*/
static int i2c_outb(struct i2c_adapter *i2c_adap, unsigned char c)
{
int i;
int sb;
int ack;
struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
/* assert: scl is low */
for (i = 7; i >= 0; i--) {
sb = (c >> i) & 1;
setsda(adap, sb);
udelay((adap->udelay + 1) / 2);
if (sclhi(adap) < 0) { /* timed out */
bit_dbg(1, &i2c_adap->dev, "i2c_outb: 0x%02x, "
"timeout at bit #%d\n", (int)c, i);
return -ETIMEDOUT;
}
/* FIXME do arbitration here:
* if (sb && !getsda(adap)) -> ouch! Get out of here.
*
* Report a unique code, so higher level code can retry
* the whole (combined) message and *NOT* issue STOP.
*/
scllo(adap);
}
sdahi(adap);
if (sclhi(adap) < 0) { /* pull high timeout, maybe slave is handling interupter event */
bit_dbg(1, &i2c_adap->dev, "i2c_outb: 0x%02x, "
"timeout at ack\n", (int)c);
return -ETIMEDOUT;
}
/* read ack: SDA should be pulled down by slave, or it may
* NAK (usually to report problems with the data we wrote).
*/
ack = !getsda(adap); /* ack: sda is pulled low -> success */
bit_dbg(2, &i2c_adap->dev, "i2c_outb: 0x%02x %s\n", (int)c,
ack ? "A" : "NA");
scllo(adap);
return ack;
/* assert: scl is low (sda undef) */
}
数据传输过程，如果是读则调用readbytes函数去读数据（主处理函数为i2c_inb），如果是写则调用sendbytes（主处理函数为i2c_outb）去写数据，代码具体实现如下：
static int sendbytes(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
{
const unsigned char *temp = msg->buf; /* sending content buffer */
int count = msg->len; /* total content length */
unsigned short nak_ok = msg->flags & I2C_M_IGNORE_NAK;
int retval;
int wrcount = 0;
while (count > 0) {
retval = i2c_outb(i2c_adap, *temp);
/* OK/ACK; or ignored NAK */
if ((retval > 0) || (nak_ok && (retval == 0))) {
count--; /* remaining content minus one byte */
temp++; /* shift to the next byte preparing for sending */
wrcount++; /*Total writing bytes increases */
/* A slave NAKing the master means the slave didn't like
* something about the data it saw. For example, maybe
* the SMBus PEC was wrong.
*/
} else if (retval == 0) {
dev_err(&i2c_adap->dev, "sendbytes: NAK bailout.\n");
return -EIO;
/* Timeout; or (someday) lost arbitration
*
* FIXME Lost ARB implies retrying the transaction from
* the first message, after the "winning" master issues
* its STOP. As a rule, upper layer code has no reason
* to know or care about this ... it is *NOT* an error.
*/
} else {
dev_err(&i2c_adap->dev, "sendbytes: error %d\n",
retval);
return retval;
}
}
return wrcount;
}
/* 读n个字节 */
static int i2c_inb(struct i2c_adapter *i2c_adap)
{
/* read byte via i2c port, without start/stop sequence */
/* acknowledge is sent in i2c_read. */
int i;
unsigned char indata = 0;
struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
/* assert: scl is low */
sdahi(adap);
for (i = 0; i < 8; i++) {
if (sclhi(adap) < 0) { /* timeout */
bit_dbg(1, &i2c_adap->dev, "i2c_inb: timeout at bit "
"#%d\n", 7 - i);
return -ETIMEDOUT;
}
indata *= 2;
if (getsda(adap))
indata |= 0x01;
setscl(adap, 0);
udelay(i == 7 ? adap->udelay / 2 : adap->udelay);
}
/* assert: scl is low */
return indata;
}
/*
* ACK 英文缩写: ACKnowledge Character
* 在数据通信传输中，接收站发给发送站的一种传输控制字符。它表示确认发来的数据已经接受无误。
* NAK 英文缩写: Negative Acknowledgment
* 否定应答或者非应答的缩写。
*/
static int acknak(struct i2c_adapter *i2c_adap, int is_ack)
{
struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
/* assert: sda is high */
if (is_ack) /* send ack */
setsda(adap, 0);
udelay((adap->udelay + 1) / 2);
if (sclhi(adap) < 0) { /* timeout */
dev_err(&i2c_adap->dev, "readbytes: ack/nak timeout\n");
return -ETIMEDOUT;
}
scllo(adap);
return 0;
}
static int readbytes(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
{
int inval;
int rdcount = 0; /* counts bytes read */
unsigned char *temp = msg->buf;
int count = msg->len;
const unsigned flags = msg->flags;
while (count > 0) {
inval = i2c_inb(i2c_adap);
if (inval >= 0) {
*temp = inval;
rdcount++;
} else { /* read timed out */
break;
}
temp++;
count--;
/* Some SMBus transactions require that we receive the
transaction length as the first read byte. */
if (rdcount == 1 && (flags & I2C_M_RECV_LEN)) {
if (inval <= 0 || inval > I2C_SMBUS_BLOCK_MAX) {
if (!(flags & I2C_M_NO_RD_ACK))
acknak(i2c_adap, 0);
dev_err(&i2c_adap->dev, "readbytes: invalid "
"block length (%d)\n", inval);
return -EPROTO;
}
/* The original count value accounts for the extra
bytes, that is, either 1 for a regular transaction,
or 2 for a PEC transaction. */
count += inval;
msg->len += inval;
}
bit_dbg(2, &i2c_adap->dev, "readbytes: 0x%02x %s\n",
inval,
(flags & I2C_M_NO_RD_ACK)
? "(no ack/nak)"
: (count ? "A" : "NA"));
if (!(flags & I2C_M_NO_RD_ACK)) {
inval = acknak(i2c_adap, count);
if (inval < 0)
return inval;
}
}
return rdcount;
}
static u32 bit_func(struct i2c_adapter *adap)
{
return I2C_FUNC_I2C | I2C_FUNC_NOSTART | I2C_FUNC_SMBUS_EMUL |
I2C_FUNC_SMBUS_READ_BLOCK_DATA |
I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
I2C_FUNC_10BIT_ADDR | I2C_FUNC_PROTOCOL_MANGLING;
}