UART 有三条线，分别是 Rx，Tx 和 GND
数据发送接收步骤：
1.双方约定波特率
2.拉低（从高电平） Tx 引脚维持 1bit 时间
3.接收端在低电平开始处计时
4.发送端根据数据驱动 Tx 引脚电平
5.接收端 1.5bit 时间后读取引脚状态（前面有一个开始位）
6.bit8 是可选的校验位（可分为奇校验和偶校验）
7.发送停止位（可以约定停止位占据多少时间）
驱动注册
/ drivers / tty / serial / imx.c
先看 init 函数，其注册了imx_uart_uart_driver 和一个平台驱动
static int __init imx_uart_init(void)
{
int ret = uart_register_driver(&imx_uart_uart_driver);
if (ret)
return ret;
ret = platform_driver_register(&imx_uart_platform_driver);
if (ret != 0)
uart_unregister_driver(&imx_uart_uart_driver);
return ret;
}
static struct uart_driver imx_uart_uart_driver = {
.owner = THIS_MODULE,
.driver_name = DRIVER_NAME,
.dev_name = DEV_NAME,
.major = SERIAL_IMX_MAJOR,
.minor = MINOR_START,
.nr = ARRAY_SIZE(imx_uart_ports),
.cons = IMX_CONSOLE,
};
static struct platform_driver imx_uart_platform_driver = {
.probe = imx_uart_probe,
.remove = imx_uart_remove,
.driver = {
.name = "imx-uart",
.of_match_table = imx_uart_dt_ids,
.pm = &imx_uart_pm_ops,
},
};
看看这个 probe 函数，这里面放入了操作函数结构体imx_uart_pops
static int imx_uart_probe(struct platform_device *pdev)
{
struct device_node *np = pdev->dev.of_node;
struct imx_port *sport;
void __iomem *base;
u32 dma_buf_conf[2];
int ret = 0;
u32 ucr1;
struct resource *res;
int txirq, rxirq, rtsirq;
sport = devm_kzalloc(&pdev->dev, sizeof(*sport), GFP_KERNEL);
if (!sport)
return -ENOMEM;
sport->devdata = of_device_get_match_data(&pdev->dev);
ret = of_alias_get_id(np, "serial");
if (ret < 0) {
dev_err(&pdev->dev, "failed to get alias id, errno %d\n", ret);
return ret;
}
sport->port.line = ret;
if (of_get_property(np, "uart-has-rtscts", NULL) ||
of_get_property(np, "fsl,uart-has-rtscts", NULL) /* deprecated */)
sport->have_rtscts = 1;
if (of_get_property(np, "fsl,dte-mode", NULL))
sport->dte_mode = 1;
if (of_get_property(np, "rts-gpios", NULL))
sport->have_rtsgpio = 1;
if (of_get_property(np, "fsl,inverted-tx", NULL))
sport->inverted_tx = 1;
if (of_get_property(np, "fsl,inverted-rx", NULL))
sport->inverted_rx = 1;
if (!of_property_read_u32_array(np, "fsl,dma-info", dma_buf_conf, 2)) {
sport->rx_period_length = dma_buf_conf[0];
sport->rx_periods = dma_buf_conf[1];
} else {
sport->rx_period_length = RX_DMA_PERIOD_LEN;
sport->rx_periods = RX_DMA_PERIODS;
}
if (sport->port.line >= ARRAY_SIZE(imx_uart_ports)) {
dev_err(&pdev->dev, "serial%d out of range\n",
sport->port.line);
return -EINVAL;
}
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
base = devm_ioremap_resource(&pdev->dev, res);
if (IS_ERR(base))
return PTR_ERR(base);
rxirq = platform_get_irq(pdev, 0);
if (rxirq < 0)
return rxirq;
txirq = platform_get_irq_optional(pdev, 1);
rtsirq = platform_get_irq_optional(pdev, 2);
sport->port.dev = &pdev->dev;
sport->port.mapbase = res->start;
sport->port.membase = base;
sport->port.type = PORT_IMX;
sport->port.iotype = UPIO_MEM;
sport->port.irq = rxirq;
sport->port.fifosize = 32;
sport->port.has_sysrq = IS_ENABLED(CONFIG_SERIAL_IMX_CONSOLE);
sport->port.ops = &imx_uart_pops;
sport->port.rs485_config = imx_uart_rs485_config;
sport->port.flags = UPF_BOOT_AUTOCONF;
timer_setup(&sport->timer, imx_uart_timeout, 0);
sport->gpios = mctrl_gpio_init(&sport->port, 0);
if (IS_ERR(sport->gpios))
return PTR_ERR(sport->gpios);
sport->clk_ipg = devm_clk_get(&pdev->dev, "ipg");
if (IS_ERR(sport->clk_ipg)) {
ret = PTR_ERR(sport->clk_ipg);
dev_err(&pdev->dev, "failed to get ipg clk: %d\n", ret);
return ret;
}
sport->clk_per = devm_clk_get(&pdev->dev, "per");
if (IS_ERR(sport->clk_per)) {
ret = PTR_ERR(sport->clk_per);
dev_err(&pdev->dev, "failed to get per clk: %d\n", ret);
return ret;
}
sport->port.uartclk = clk_get_rate(sport->clk_per);
/* For register access, we only need to enable the ipg clock. */
ret = clk_prepare_enable(sport->clk_ipg);
if (ret) {
dev_err(&pdev->dev, "failed to enable per clk: %d\n", ret);
return ret;
}
/* initialize shadow register values */
sport->ucr1 = readl(sport->port.membase + UCR1);
sport->ucr2 = readl(sport->port.membase + UCR2);
sport->ucr3 = readl(sport->port.membase + UCR3);
sport->ucr4 = readl(sport->port.membase + UCR4);
sport->ufcr = readl(sport->port.membase + UFCR);
ret = uart_get_rs485_mode(&sport->port);
if (ret) {
clk_disable_unprepare(sport->clk_ipg);
return ret;
}
if (sport->port.rs485.flags & SER_RS485_ENABLED &&
(!sport->have_rtscts && !sport->have_rtsgpio))
dev_err(&pdev->dev, "no RTS control, disabling rs485\n");
/*
* If using the i.MX UART RTS/CTS control then the RTS (CTS_B)
* signal cannot be set low during transmission in case the
* receiver is off (limitation of the i.MX UART IP).
*/
if (sport->port.rs485.flags & SER_RS485_ENABLED &&
sport->have_rtscts && !sport->have_rtsgpio &&
(!(sport->port.rs485.flags & SER_RS485_RTS_ON_SEND) &&
!(sport->port.rs485.flags & SER_RS485_RX_DURING_TX)))
dev_err(&pdev->dev,
"low-active RTS not possible when receiver is off, enabling receiver\n");
imx_uart_rs485_config(&sport->port, &sport->port.rs485);
/* Disable interrupts before requesting them */
ucr1 = imx_uart_readl(sport, UCR1);
ucr1 &= ~(UCR1_ADEN | UCR1_TRDYEN | UCR1_IDEN | UCR1_RRDYEN | UCR1_RTSDEN);
imx_uart_writel(sport, ucr1, UCR1);
if (!imx_uart_is_imx1(sport) && sport->dte_mode) {
/*
* The DCEDTE bit changes the direction of DSR, DCD, DTR and RI
* and influences if UCR3_RI and UCR3_DCD changes the level of RI
* and DCD (when they are outputs) or enables the respective
* irqs. So set this bit early, i.e. before requesting irqs.
*/
u32 ufcr = imx_uart_readl(sport, UFCR);
if (!(ufcr & UFCR_DCEDTE))
imx_uart_writel(sport, ufcr | UFCR_DCEDTE, UFCR);
/*
* Disable UCR3_RI and UCR3_DCD irqs. They are also not
* enabled later because they cannot be cleared
* (confirmed on i.MX25) which makes them unusable.
*/
imx_uart_writel(sport,
IMX21_UCR3_RXDMUXSEL | UCR3_ADNIMP | UCR3_DSR,
UCR3);
} else {
u32 ucr3 = UCR3_DSR;
u32 ufcr = imx_uart_readl(sport, UFCR);
if (ufcr & UFCR_DCEDTE)
imx_uart_writel(sport, ufcr & ~UFCR_DCEDTE, UFCR);
if (!imx_uart_is_imx1(sport))
ucr3 |= IMX21_UCR3_RXDMUXSEL | UCR3_ADNIMP;
imx_uart_writel(sport, ucr3, UCR3);
}
clk_disable_unprepare(sport->clk_ipg);
hrtimer_init(&sport->trigger_start_tx, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
hrtimer_init(&sport->trigger_stop_tx, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
sport->trigger_start_tx.function = imx_trigger_start_tx;
sport->trigger_stop_tx.function = imx_trigger_stop_tx;
/*
* Allocate the IRQ(s) i.MX1 has three interrupts whereas later
* chips only have one interrupt.
*/
if (txirq > 0) {
ret = devm_request_irq(&pdev->dev, rxirq, imx_uart_rxint, 0,
dev_name(&pdev->dev), sport);
if (ret) {
dev_err(&pdev->dev, "failed to request rx irq: %d\n",
ret);
return ret;
}
ret = devm_request_irq(&pdev->dev, txirq, imx_uart_txint, 0,
dev_name(&pdev->dev), sport);
if (ret) {
dev_err(&pdev->dev, "failed to request tx irq: %d\n",
ret);
return ret;
}
ret = devm_request_irq(&pdev->dev, rtsirq, imx_uart_rtsint, 0,
dev_name(&pdev->dev), sport);
if (ret) {
dev_err(&pdev->dev, "failed to request rts irq: %d\n",
ret);
return ret;
}
} else {
ret = devm_request_irq(&pdev->dev, rxirq, imx_uart_int, 0,
dev_name(&pdev->dev), sport);
if (ret) {
dev_err(&pdev->dev, "failed to request irq: %d\n", ret);
return ret;
}
}
imx_uart_ports[sport->port.line] = sport;
platform_set_drvdata(pdev, sport);
return uart_add_one_port(&imx_uart_uart_driver, &sport->port);
}
static const struct uart_ops imx_uart_pops = {
.tx_empty = imx_uart_tx_empty,
.set_mctrl = imx_uart_set_mctrl,
.get_mctrl = imx_uart_get_mctrl,
.stop_tx = imx_uart_stop_tx,
.start_tx = imx_uart_start_tx,
.stop_rx = imx_uart_stop_rx,
.enable_ms = imx_uart_enable_ms,
.break_ctl = imx_uart_break_ctl,
.startup = imx_uart_startup,
.shutdown = imx_uart_shutdown,
.flush_buffer = imx_uart_flush_buffer,
.set_termios = imx_uart_set_termios,
.type = imx_uart_type,
.config_port = imx_uart_config_port,
.verify_port = imx_uart_verify_port,
#if defined(CONFIG_CONSOLE_POLL)
.poll_init = imx_uart_poll_init,
.poll_get_char = imx_uart_poll_get_char,
.poll_put_char = imx_uart_poll_put_char,
#endif
};
来看看前面注册imx_uart_uart_driver 的过程，这里初始化并注册了tty_driver，注意这里把前面那个uart_ops 给了tty_driver，这里还给驱动分配了一个state
/**
* uart_register_driver - register a driver with the uart core layer
* @drv: low level driver structure
*
* Register a uart driver with the core driver. We in turn register
* with the tty layer, and initialise the core driver per-port state.
*
* We have a proc file in /proc/tty/driver which is named after the
* normal driver.
*
* drv->port should be NULL, and the per-port structures should be
* registered using uart_add_one_port after this call has succeeded.
*/
int uart_register_driver(struct uart_driver *drv)
{
struct tty_driver *normal;
int i, retval = -ENOMEM;
BUG_ON(drv->state);
/*
* Maybe we should be using a slab cache for this, especially if
* we have a large number of ports to handle.
*/
drv->state = kcalloc(drv->nr, sizeof(struct uart_state), GFP_KERNEL);
if (!drv->state)
goto out;
normal = tty_alloc_driver(drv->nr, TTY_DRIVER_REAL_RAW |
TTY_DRIVER_DYNAMIC_DEV);
if (IS_ERR(normal)) {
retval = PTR_ERR(normal);
goto out_kfree;
}
drv->tty_driver = normal;
normal->driver_name = drv->driver_name;
normal->name = drv->dev_name;
normal->major = drv->major;
normal->minor_start = drv->minor;
normal->type = TTY_DRIVER_TYPE_SERIAL;
normal->subtype = SERIAL_TYPE_NORMAL;
normal->init_termios = tty_std_termios;
normal->init_termios.c_cflag = B9600 | CS8 | CREAD | HUPCL | CLOCAL;
normal->init_termios.c_ispeed = normal->init_termios.c_ospeed = 9600;
normal->driver_state = drv;
tty_set_operations(normal, &uart_ops);
/*
* Initialise the UART state(s).
*/
for (i = 0; i < drv->nr; i++) {
struct uart_state *state = drv->state + i;
struct tty_port *port = &state->port;
tty_port_init(port);
port->ops = &uart_port_ops;
}
retval = tty_register_driver(normal);
if (retval >= 0)
return retval;
for (i = 0; i < drv->nr; i++)
tty_port_destroy(&drv->state[i].port);
tty_driver_kref_put(normal);
out_kfree:
kfree(drv->state);
out:
return retval;
}
EXPORT_SYMBOL(uart_register_driver);
来看看tty_alloc_driver
/* Use TTY_DRIVER_* flags below */
#define tty_alloc_driver(lines, flags) \
__tty_alloc_driver(lines, THIS_MODULE, flags)
这里分配了 cdev，数量等于 port 数量
每个串口都有 ports ttys termios cdevs
/**
* __tty_alloc_driver -- allocate tty driver
* @lines: count of lines this driver can handle at most
* @owner: module which is responsible for this driver
* @flags: some of %TTY_DRIVER_ flags, will be set in driver->flags
*
* This should not be called directly, some of the provided macros should be
* used instead. Use IS_ERR() and friends on @retval.
*/
struct tty_driver *__tty_alloc_driver(unsigned int lines, struct module *owner,
unsigned long flags)
{
struct tty_driver *driver;
unsigned int cdevs = 1;
int err;
if (!lines || (flags & TTY_DRIVER_UNNUMBERED_NODE && lines > 1))
return ERR_PTR(-EINVAL);
driver = kzalloc(sizeof(*driver), GFP_KERNEL);
if (!driver)
return ERR_PTR(-ENOMEM);
kref_init(&driver->kref);
driver->magic = TTY_DRIVER_MAGIC;
driver->num = lines;
driver->owner = owner;
driver->flags = flags;
if (!(flags & TTY_DRIVER_DEVPTS_MEM)) {
driver->ttys = kcalloc(lines, sizeof(*driver->ttys),
GFP_KERNEL);
driver->termios = kcalloc(lines, sizeof(*driver->termios),
GFP_KERNEL);
if (!driver->ttys || !driver->termios) {
err = -ENOMEM;
goto err_free_all;
}
}
if (!(flags & TTY_DRIVER_DYNAMIC_ALLOC)) {
driver->ports = kcalloc(lines, sizeof(*driver->ports),
GFP_KERNEL);
if (!driver->ports) {
err = -ENOMEM;
goto err_free_all;
}
cdevs = lines;
}
driver->cdevs = kcalloc(cdevs, sizeof(*driver->cdevs), GFP_KERNEL);
if (!driver->cdevs) {
err = -ENOMEM;
goto err_free_all;
}
return driver;
err_free_all:
kfree(driver->ports);
kfree(driver->ttys);
kfree(driver->termios);
kfree(driver->cdevs);
kfree(driver);
return ERR_PTR(err);
}
EXPORT_SYMBOL(__tty_alloc_driver);
看看 probe 函数的最后一步uart_add_one_port
/ drivers / tty / serial / serial_core.c
/**
* uart_add_one_port - attach a driver-defined port structure
* @drv: pointer to the uart low level driver structure for this port
* @uport: uart port structure to use for this port.
*
* Context: task context, might sleep
*
* This allows the driver to register its own uart_port structure
* with the core driver. The main purpose is to allow the low
* level uart drivers to expand uart_port, rather than having yet
* more levels of structures.
*/
int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
{
struct uart_state *state;
struct tty_port *port;
int ret = 0;
struct device *tty_dev;
int num_groups;
if (uport->line >= drv->nr)
return -EINVAL;
state = drv->state + uport->line;
port = &state->port;
mutex_lock(&port_mutex);
mutex_lock(&port->mutex);
if (state->uart_port) {
ret = -EINVAL;
goto out;
}
/* Link the port to the driver state table and vice versa */
atomic_set(&state->refcount, 1);
init_waitqueue_head(&state->remove_wait);
state->uart_port = uport;
uport->state = state;
state->pm_state = UART_PM_STATE_UNDEFINED;
uport->cons = drv->cons;
uport->minor = drv->tty_driver->minor_start + uport->line;
uport->name = kasprintf(GFP_KERNEL, "%s%d", drv->dev_name,
drv->tty_driver->name_base + uport->line);
if (!uport->name) {
ret = -ENOMEM;
goto out;
}
/*
* If this port is in use as a console then the spinlock is already
* initialised.
*/
if (!uart_console_enabled(uport))
uart_port_spin_lock_init(uport);
if (uport->cons && uport->dev)
of_console_check(uport->dev->of_node, uport->cons->name, uport->line);
tty_port_link_device(port, drv->tty_driver, uport->line);
uart_configure_port(drv, state, uport);
port->console = uart_console(uport);
num_groups = 2;
if (uport->attr_group)
num_groups++;
uport->tty_groups = kcalloc(num_groups, sizeof(*uport->tty_groups),
GFP_KERNEL);
if (!uport->tty_groups) {
ret = -ENOMEM;
goto out;
}
uport->tty_groups[0] = &tty_dev_attr_group;
if (uport->attr_group)
uport->tty_groups[1] = uport->attr_group;
/*
* Register the port whether it's detected or not. This allows
* setserial to be used to alter this port's parameters.
*/
tty_dev = tty_port_register_device_attr_serdev(port, drv->tty_driver,
uport->line, uport->dev, port, uport->tty_groups);
if (!IS_ERR(tty_dev)) {
device_set_wakeup_capable(tty_dev, 1);
} else {
dev_err(uport->dev, "Cannot register tty device on line %d\n",
uport->line);
}
/*
* Ensure UPF_DEAD is not set.
*/
uport->flags &= ~UPF_DEAD;
out:
mutex_unlock(&port->mutex);
mutex_unlock(&port_mutex);
return ret;
}
EXPORT_SYMBOL(uart_add_one_port);
/ drivers / tty / tty_port.c
/**
* tty_port_register_device_attr_serdev - register tty or serdev device
* @port: tty_port of the device
* @driver: tty_driver for this device
* @index: index of the tty
* @device: parent if exists, otherwise NULL
* @drvdata: driver data for the device
* @attr_grp: attribute group for the device
*
* Register a serdev or tty device depending on if the parent device has any
* defined serdev clients or not.
*/
struct device *tty_port_register_device_attr_serdev(struct tty_port *port,
struct tty_driver *driver, unsigned index,
struct device *device, void *drvdata,
const struct attribute_group **attr_grp)
{
struct device *dev;
tty_port_link_device(port, driver, index);
dev = serdev_tty_port_register(port, device, driver, index);
if (PTR_ERR(dev) != -ENODEV) {
/* Skip creating cdev if we registered a serdev device */
return dev;
}
return tty_register_device_attr(driver, index, device, drvdata,
attr_grp);
}
EXPORT_SYMBOL_GPL(tty_port_register_device_attr_serdev);
/**
* tty_port_link_device - link tty and tty_port
* @port: tty_port of the device
* @driver: tty_driver for this device
* @index: index of the tty
*
* Provide the tty layer with a link from a tty (specified by @index) to a
* tty_port (@port). Use this only if neither tty_port_register_device() nor
* tty_port_install() is used in the driver. If used, this has to be called
* before tty_register_driver().
*/
void tty_port_link_device(struct tty_port *port,
struct tty_driver *driver, unsigned index)
{
if (WARN_ON(index >= driver->num))
return;
driver->ports[index] = port;
}
EXPORT_SYMBOL_GPL(tty_port_link_device);
这里调用了tty_cdev_add
/**
* tty_register_device_attr - register a tty device
* @driver: the tty driver that describes the tty device
* @index: the index in the tty driver for this tty device
* @device: a struct device that is associated with this tty device.
* This field is optional, if there is no known struct device
* for this tty device it can be set to %NULL safely.
* @drvdata: Driver data to be set to device.
* @attr_grp: Attribute group to be set on device.
*
* This call is required to be made to register an individual tty device if the
* tty driver's flags have the %TTY_DRIVER_DYNAMIC_DEV bit set. If that bit is
* not set, this function should not be called by a tty driver.
*
* Locking: ??
*
* Return: A pointer to the struct device for this tty device (or
* ERR_PTR(-EFOO) on error).
*/
struct device *tty_register_device_attr(struct tty_driver *driver,
unsigned index, struct device *device,
void *drvdata,
const struct attribute_group **attr_grp)
{
char name[64];
dev_t devt = MKDEV(driver->major, driver->minor_start) + index;
struct ktermios *tp;
struct device *dev;
int retval;
if (index >= driver->num) {
pr_err("%s: Attempt to register invalid tty line number (%d)\n",
driver->name, index);
return ERR_PTR(-EINVAL);
}
if (driver->type == TTY_DRIVER_TYPE_PTY)
pty_line_name(driver, index, name);
else
tty_line_name(driver, index, name);
dev = kzalloc(sizeof(*dev), GFP_KERNEL);
if (!dev)
return ERR_PTR(-ENOMEM);
dev->devt = devt;
dev->class = tty_class;
dev->parent = device;
dev->release = tty_device_create_release;
dev_set_name(dev, "%s", name);
dev->groups = attr_grp;
dev_set_drvdata(dev, drvdata);
dev_set_uevent_suppress(dev, 1);
retval = device_register(dev);
if (retval)
goto err_put;
if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)) {
/*
* Free any saved termios data so that the termios state is
* reset when reusing a minor number.
*/
tp = driver->termios[index];
if (tp) {
driver->termios[index] = NULL;
kfree(tp);
}
retval = tty_cdev_add(driver, devt, index, 1);
if (retval)
goto err_del;
}
dev_set_uevent_suppress(dev, 0);
kobject_uevent(&dev->kobj, KOBJ_ADD);
return dev;
err_del:
device_del(dev);
err_put:
put_device(dev);
return ERR_PTR(retval);
}
EXPORT_SYMBOL_GPL(tty_register_device_attr);
这个函数中添加了cdevs 的操作函数tty_fops
static int tty_cdev_add(struct tty_driver *driver, dev_t dev,
unsigned int index, unsigned int count)
{
int err;
/* init here, since reused cdevs cause crashes */
driver->cdevs[index] = cdev_alloc();
if (!driver->cdevs[index])
return -ENOMEM;
driver->cdevs[index]->ops = &tty_fops;
driver->cdevs[index]->owner = driver->owner;
err = cdev_add(driver->cdevs[index], dev, count);
if (err)
kobject_put(&driver->cdevs[index]->kobj);
return err;
}
static const struct file_operations tty_fops = {
.llseek = no_llseek,
.read_iter = tty_read,
.write_iter = tty_write,
.splice_read = generic_file_splice_read,
.splice_write = iter_file_splice_write,
.poll = tty_poll,
.unlocked_ioctl = tty_ioctl,
.compat_ioctl = tty_compat_ioctl,
.open = tty_open,
.release = tty_release,
.fasync = tty_fasync,
.show_fdinfo = tty_show_fdinfo,
};
对外的接口就是这些函数了，这里分析一下 open 的流程，其他流程都是类似的
open
/**
* tty_open - open a tty device
* @inode: inode of device file
* @filp: file pointer to tty
*
* tty_open() and tty_release() keep up the tty count that contains the number
* of opens done on a tty. We cannot use the inode-count, as different inodes
* might point to the same tty.
*
* Open-counting is needed for pty masters, as well as for keeping track of
* serial lines: DTR is dropped when the last close happens.
* (This is not done solely through tty->count, now. - Ted 1/27/92)
*
* The termios state of a pty is reset on the first open so that settings don't
* persist across reuse.
*
* Locking:
* * %tty_mutex protects tty, tty_lookup_driver() and tty_init_dev().
* * @tty->count should protect the rest.
* * ->siglock protects ->signal/->sighand
*
* Note: the tty_unlock/lock cases without a ref are only safe due to %tty_mutex
*/
static int tty_open(struct inode *inode, struct file *filp)
{
struct tty_struct *tty;
int noctty, retval;
dev_t device = inode->i_rdev;
unsigned saved_flags = filp->f_flags;
nonseekable_open(inode, filp);
retry_open:
retval = tty_alloc_file(filp);
if (retval)
return -ENOMEM;
tty = tty_open_current_tty(device, filp);
if (!tty)
tty = tty_open_by_driver(device, filp);
if (IS_ERR(tty)) {
tty_free_file(filp);
retval = PTR_ERR(tty);
if (retval != -EAGAIN || signal_pending(current))
return retval;
schedule();
goto retry_open;
}
tty_add_file(tty, filp);
check_tty_count(tty, __func__);
tty_debug_hangup(tty, "opening (count=%d)\n", tty->count);
if (tty->ops->open)
retval = tty->ops->open(tty, filp);
else
retval = -ENODEV;
filp->f_flags = saved_flags;
if (retval) {
tty_debug_hangup(tty, "open error %d, releasing\n", retval);
tty_unlock(tty); /* need to call tty_release without BTM */
tty_release(inode, filp);
if (retval != -ERESTARTSYS)
return retval;
if (signal_pending(current))
return retval;
schedule();
/*
* Need to reset f_op in case a hangup happened.
*/
if (tty_hung_up_p(filp))
filp->f_op = &tty_fops;
goto retry_open;
}
clear_bit(TTY_HUPPED, &tty->flags);
noctty = (filp->f_flags & O_NOCTTY) ||
(IS_ENABLED(CONFIG_VT) && device == MKDEV(TTY_MAJOR, 0)) ||
device == MKDEV(TTYAUX_MAJOR, 1) ||
(tty->driver->type == TTY_DRIVER_TYPE_PTY &&
tty->driver->subtype == PTY_TYPE_MASTER);
if (!noctty)
tty_open_proc_set_tty(filp, tty);
tty_unlock(tty);
return 0;
}
这里从 tty 驱动中获取tty_struct，tty_struct 代表了一个 tty 设备
static struct tty_struct *tty_open_by_driver(dev_t device,
struct file *filp)
{
struct tty_struct *tty;
struct tty_driver *driver = NULL;
int index = -1;
int retval;
mutex_lock(&tty_mutex);
driver = tty_lookup_driver(device, filp, &index);
if (IS_ERR(driver)) {
mutex_unlock(&tty_mutex);
return ERR_CAST(driver);
}
/* check whether we're reopening an existing tty */
tty = tty_driver_lookup_tty(driver, filp, index);
if (IS_ERR(tty)) {
mutex_unlock(&tty_mutex);
goto out;
}
if (tty) {
if (tty_port_kopened(tty->port)) {
tty_kref_put(tty);
mutex_unlock(&tty_mutex);
tty = ERR_PTR(-EBUSY);
goto out;
}
mutex_unlock(&tty_mutex);
retval = tty_lock_interruptible(tty);
tty_kref_put(tty); /* drop kref from tty_driver_lookup_tty() */
if (retval) {
if (retval == -EINTR)
retval = -ERESTARTSYS;
tty = ERR_PTR(retval);
goto out;
}
retval = tty_reopen(tty);
if (retval < 0) {
tty_unlock(tty);
tty = ERR_PTR(retval);
}
} else { /* Returns with the tty_lock held for now */
tty = tty_init_dev(driver, index);
mutex_unlock(&tty_mutex);
}
out:
tty_driver_kref_put(driver);
return tty;
}
回到tty_open 的处理，里面进行了tty->ops->open 这样的操作，这个是之前在核心层注册的
static const struct tty_operations uart_ops = {
.install = uart_install,
.open = uart_open,
.close = uart_close,
.write = uart_write,
.put_char = uart_put_char,
.flush_chars = uart_flush_chars,
.write_room = uart_write_room,
.chars_in_buffer= uart_chars_in_buffer,
.flush_buffer = uart_flush_buffer,
.ioctl = uart_ioctl,
.throttle = uart_throttle,
.unthrottle = uart_unthrottle,
.send_xchar = uart_send_xchar,
.set_termios = uart_set_termios,
.set_ldisc = uart_set_ldisc,
.stop = uart_stop,
.start = uart_start,
.hangup = uart_hangup,
.break_ctl = uart_break_ctl,
.wait_until_sent= uart_wait_until_sent,
#ifdef CONFIG_PROC_FS
.proc_show = uart_proc_show,
#endif
.tiocmget = uart_tiocmget,
.tiocmset = uart_tiocmset,
.set_serial = uart_set_info_user,
.get_serial = uart_get_info_user,
.get_icount = uart_get_icount,
#ifdef CONFIG_CONSOLE_POLL
.poll_init = uart_poll_init,
.poll_get_char = uart_poll_get_char,
.poll_put_char = uart_poll_put_char,
#endif
};
static int uart_open(struct tty_struct *tty, struct file *filp)
{
struct uart_state *state = tty->driver_data;
int retval;
retval = tty_port_open(&state->port, tty, filp);
if (retval > 0)
retval = 0;
return retval;
}
这里面就是调用的激活函数
int tty_port_open(struct tty_port *port, struct tty_struct *tty,
struct file *filp)
{
spin_lock_irq(&port->lock);
++port->count;
spin_unlock_irq(&port->lock);
tty_port_tty_set(port, tty);
/*
* Do the device-specific open only if the hardware isn't
* already initialized. Serialize open and shutdown using the
* port mutex.
*/
mutex_lock(&port->mutex);
if (!tty_port_initialized(port)) {
clear_bit(TTY_IO_ERROR, &tty->flags);
if (port->ops->activate) {
int retval = port->ops->activate(port, tty);
if (retval) {
mutex_unlock(&port->mutex);
return retval;
}
}
tty_port_set_initialized(port, 1);
}
mutex_unlock(&port->mutex);
return tty_port_block_til_ready(port, tty, filp);
}
EXPORT_SYMBOL(tty_port_open);
/ drivers / tty / serial / serial_core.c
static int uart_port_activate(struct tty_port *port, struct tty_struct *tty)
{
struct uart_state *state = container_of(port, struct uart_state, port);
struct uart_port *uport;
int ret;
uport = uart_port_check(state);
if (!uport || uport->flags & UPF_DEAD)
return -ENXIO;
/*
* Start up the serial port.
*/
ret = uart_startup(tty, state, 0);
if (ret > 0)
tty_port_set_active(port, 1);
return ret;
}
static int uart_startup(struct tty_struct *tty, struct uart_state *state,
int init_hw)
{
struct tty_port *port = &state->port;
int retval;
if (tty_port_initialized(port))
return 0;
retval = uart_port_startup(tty, state, init_hw);
if (retval)
set_bit(TTY_IO_ERROR, &tty->flags);
return retval;
}
这里面就调用到了前面给 port 注册的 ops 的函数了
static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
int init_hw)
{
struct uart_port *uport = uart_port_check(state);
unsigned long flags;
unsigned long page;
int retval = 0;
if (uport->type == PORT_UNKNOWN)
return 1;
/*
* Make sure the device is in D0 state.
*/
uart_change_pm(state, UART_PM_STATE_ON);
/*
* Initialise and allocate the transmit and temporary
* buffer.
*/
page = get_zeroed_page(GFP_KERNEL);
if (!page)
return -ENOMEM;
uart_port_lock(state, flags);
if (!state->xmit.buf) {
state->xmit.buf = (unsigned char *) page;
uart_circ_clear(&state->xmit);
uart_port_unlock(uport, flags);
} else {
uart_port_unlock(uport, flags);
/*
* Do not free() the page under the port lock, see
* uart_shutdown().
*/
free_page(page);
}
retval = uport->ops->startup(uport);
if (retval == 0) {
if (uart_console(uport) && uport->cons->cflag) {
tty->termios.c_cflag = uport->cons->cflag;
tty->termios.c_ispeed = uport->cons->ispeed;
tty->termios.c_ospeed = uport->cons->ospeed;
uport->cons->cflag = 0;
uport->cons->ispeed = 0;
uport->cons->ospeed = 0;
}
/*
* Initialise the hardware port settings.
*/
uart_change_speed(tty, state, NULL);
/*
* Setup the RTS and DTR signals once the
* port is open and ready to respond.
*/
if (init_hw && C_BAUD(tty))
uart_port_dtr_rts(uport, 1);
}
/*
* This is to allow setserial on this port. People may want to set
* port/irq/type and then reconfigure the port properly if it failed
* now.
*/
if (retval && capable(CAP_SYS_ADMIN))
return 1;
return retval;
}
/ drivers / tty / serial / imx.c
static int imx_uart_startup(struct uart_port *port)
{
struct imx_port *sport = (struct imx_port *)port;
int retval, i;
unsigned long flags;
int dma_is_inited = 0;
u32 ucr1, ucr2, ucr3, ucr4;
retval = clk_prepare_enable(sport->clk_per);
if (retval)
return retval;
retval = clk_prepare_enable(sport->clk_ipg);
if (retval) {
clk_disable_unprepare(sport->clk_per);
return retval;
}
imx_uart_setup_ufcr(sport, TXTL_DEFAULT, RXTL_DEFAULT);
/* disable the DREN bit (Data Ready interrupt enable) before
* requesting IRQs
*/
ucr4 = imx_uart_readl(sport, UCR4);
/* set the trigger level for CTS */
ucr4 &= ~(UCR4_CTSTL_MASK << UCR4_CTSTL_SHF);
ucr4 |= CTSTL << UCR4_CTSTL_SHF;
imx_uart_writel(sport, ucr4 & ~UCR4_DREN, UCR4);
/* Can we enable the DMA support? */
if (!uart_console(port) && imx_uart_dma_init(sport) == 0)
dma_is_inited = 1;
spin_lock_irqsave(&sport->port.lock, flags);
/* Reset fifo's and state machines */
i = 100;
ucr2 = imx_uart_readl(sport, UCR2);
ucr2 &= ~UCR2_SRST;
imx_uart_writel(sport, ucr2, UCR2);
while (!(imx_uart_readl(sport, UCR2) & UCR2_SRST) && (--i > 0))
udelay(1);
/*
* Finally, clear and enable interrupts
*/
imx_uart_writel(sport, USR1_RTSD | USR1_DTRD, USR1);
imx_uart_writel(sport, USR2_ORE, USR2);
ucr1 = imx_uart_readl(sport, UCR1) & ~UCR1_RRDYEN;
ucr1 |= UCR1_UARTEN;
if (sport->have_rtscts)
ucr1 |= UCR1_RTSDEN;
imx_uart_writel(sport, ucr1, UCR1);
ucr4 = imx_uart_readl(sport, UCR4) & ~(UCR4_OREN | UCR4_INVR);
if (!dma_is_inited)
ucr4 |= UCR4_OREN;
if (sport->inverted_rx)
ucr4 |= UCR4_INVR;
imx_uart_writel(sport, ucr4, UCR4);
ucr3 = imx_uart_readl(sport, UCR3) & ~UCR3_INVT;
/*
* configure tx polarity before enabling tx
*/
if (sport->inverted_tx)
ucr3 |= UCR3_INVT;
if (!imx_uart_is_imx1(sport)) {
ucr3 |= UCR3_DTRDEN | UCR3_RI | UCR3_DCD;
if (sport->dte_mode)
/* disable broken interrupts */
ucr3 &= ~(UCR3_RI | UCR3_DCD);
}
imx_uart_writel(sport, ucr3, UCR3);
ucr2 = imx_uart_readl(sport, UCR2) & ~UCR2_ATEN;
ucr2 |= (UCR2_RXEN | UCR2_TXEN);
if (!sport->have_rtscts)
ucr2 |= UCR2_IRTS;
/*
* make sure the edge sensitive RTS-irq is disabled,
* we're using RTSD instead.
*/
if (!imx_uart_is_imx1(sport))
ucr2 &= ~UCR2_RTSEN;
imx_uart_writel(sport, ucr2, UCR2);
/*
* Enable modem status interrupts
*/
imx_uart_enable_ms(&sport->port);
if (dma_is_inited) {
imx_uart_enable_dma(sport);
imx_uart_start_rx_dma(sport);
} else {
ucr1 = imx_uart_readl(sport, UCR1);
ucr1 |= UCR1_RRDYEN;
imx_uart_writel(sport, ucr1, UCR1);
ucr2 = imx_uart_readl(sport, UCR2);
ucr2 |= UCR2_ATEN;
imx_uart_writel(sport, ucr2, UCR2);
}
spin_unlock_irqrestore(&sport->port.lock, flags);
return 0;
}