Linux kernel 之 uart 驱动解析
uart 是一种非常之常见的总线，比如DEBUG信息输出，小数据量数据传输，485，以及蓝牙的控制，GPS，很多都是通过uart 进行数据传输并进行控制。
* #### 在Linux kernel 内部，uart 通常是作为 一个 tty 设备对其进行控制，也是就是一个字符设备文件，可对其进行读写操作。
* #### kernel version 4.4.12
* #### 首先先看一下基本的 结构体 和 API 操作。
```c
// include/linux/serial_core.h
// uart 驱动结构体
struct uart_driver {
struct module *owner;
const char *driver_name; // 驱动名字
const char *dev_name; // 设备名字
int major; // 主设备号
int minor; // 次设备号
int nr;
struct console *cons; // 看似控制台结构体
/*
* these are private; the low level driver should not
* touch these; they should be initialised to NULL
*/
struct uart_state *state; // 状态结构体
struct tty_driver *tty_driver; // tty 驱动结构体
};
struct uart_port {
spinlock_t lock; /* port lock */
unsigned long iobase; /* in/out[bwl] */
unsigned char __iomem *membase; /* read/write[bwl] */
unsigned int (*serial_in)(struct uart_port *, int);
void (*serial_out)(struct uart_port *, int, int);
void (*set_termios)(struct uart_port *,
struct ktermios *new,
struct ktermios *old);
void (*set_mctrl)(struct uart_port *, unsigned int);
int (*startup)(struct uart_port *port);
void (*shutdown)(struct uart_port *port);
void (*throttle)(struct uart_port *port);
void (*unthrottle)(struct uart_port *port);
int (*handle_irq)(struct uart_port *);
void (*pm)(struct uart_port *, unsigned int state,
unsigned int old);
void (*handle_break)(struct uart_port *);
int (*rs485_config)(struct uart_port *,
struct serial_rs485 *rs485);
unsigned int irq; /* irq number */
unsigned long irqflags; /* irq flags */
unsigned int uartclk; /* base uart clock */
unsigned int fifosize; /* tx fifo size */
unsigned char x_char; /* xon/xoff char */
unsigned char regshift; /* reg offset shift */
unsigned char iotype; /* io access style */
unsigned char unused1;
#define UPIO_PORT (SERIAL_IO_PORT) /* 8b I/O port access */
#define UPIO_HUB6 (SERIAL_IO_HUB6) /* Hub6 ISA card */
#define UPIO_MEM (SERIAL_IO_MEM) /* 8b MMIO access */
#define UPIO_MEM32 (SERIAL_IO_MEM32) /* 32b little endian */
#define UPIO_AU (SERIAL_IO_AU) /* Au1x00 and RT288x type IO */
#define UPIO_TSI (SERIAL_IO_TSI) /* Tsi108/109 type IO */
#define UPIO_MEM32BE (SERIAL_IO_MEM32BE) /* 32b big endian */
unsigned int read_status_mask; /* driver specific */
unsigned int ignore_status_mask; /* driver specific */
struct uart_state *state; /* pointer to parent state */
struct uart_icount icount; /* statistics */
struct console *cons; /* struct console, if any */
#if defined(CONFIG_SERIAL_CORE_CONSOLE) || defined(SUPPORT_SYSRQ)
unsigned long sysrq; /* sysrq timeout */
#endif
/* flags must be updated while holding port mutex */
upf_t flags;
/*
* These flags must be equivalent to the flags defined in
* include/uapi/linux/tty_flags.h which are the userspace definitions
* assigned from the serial_struct flags in uart_set_info()
* [for bit definitions in the UPF_CHANGE_MASK]
*
* Bits [0..UPF_LAST_USER] are userspace defined/visible/changeable
* except bit 15 (UPF_NO_TXEN_TEST) which is masked off.
* The remaining bits are serial-core specific and not modifiable by
* userspace.
*/
#define UPF_FOURPORT ((__force upf_t) ASYNC_FOURPORT /* 1 */ )
#define UPF_SAK ((__force upf_t) ASYNC_SAK /* 2 */ )
#define UPF_SPD_HI ((__force upf_t) ASYNC_SPD_HI /* 4 */ )
#define UPF_SPD_VHI ((__force upf_t) ASYNC_SPD_VHI /* 5 */ )
#define UPF_SPD_CUST ((__force upf_t) ASYNC_SPD_CUST /* 0x0030 */ )
#define UPF_SPD_WARP ((__force upf_t) ASYNC_SPD_WARP /* 0x1010 */ )
#define UPF_SPD_MASK ((__force upf_t) ASYNC_SPD_MASK /* 0x1030 */ )
#define UPF_SKIP_TEST ((__force upf_t) ASYNC_SKIP_TEST /* 6 */ )
#define UPF_AUTO_IRQ ((__force upf_t) ASYNC_AUTO_IRQ /* 7 */ )
#define UPF_HARDPPS_CD ((__force upf_t) ASYNC_HARDPPS_CD /* 11 */ )
#define UPF_SPD_SHI ((__force upf_t) ASYNC_SPD_SHI /* 12 */ )
#define UPF_LOW_LATENCY ((__force upf_t) ASYNC_LOW_LATENCY /* 13 */ )
#define UPF_BUGGY_UART ((__force upf_t) ASYNC_BUGGY_UART /* 14 */ )
#define UPF_NO_TXEN_TEST ((__force upf_t) (1 << 15))
#define UPF_MAGIC_MULTIPLIER ((__force upf_t) ASYNC_MAGIC_MULTIPLIER /* 16 */ )
/* Port has hardware-assisted h/w flow control */
#define UPF_AUTO_CTS ((__force upf_t) (1 << 20))
#define UPF_AUTO_RTS ((__force upf_t) (1 << 21))
#define UPF_HARD_FLOW ((__force upf_t) (UPF_AUTO_CTS | UPF_AUTO_RTS))
/* Port has hardware-assisted s/w flow control */
#define UPF_SOFT_FLOW ((__force upf_t) (1 << 22))
#define UPF_CONS_FLOW ((__force upf_t) (1 << 23))
#define UPF_SHARE_IRQ ((__force upf_t) (1 << 24))
#define UPF_EXAR_EFR ((__force upf_t) (1 << 25))
#define UPF_BUG_THRE ((__force upf_t) (1 << 26))
/* The exact UART type is known and should not be probed. */
#define UPF_FIXED_TYPE ((__force upf_t) (1 << 27))
#define UPF_BOOT_AUTOCONF ((__force upf_t) (1 << 28))
#define UPF_FIXED_PORT ((__force upf_t) (1 << 29))
#define UPF_DEAD ((__force upf_t) (1 << 30))
#define UPF_IOREMAP ((__force upf_t) (1 << 31))
#define __UPF_CHANGE_MASK 0x17fff
#define UPF_CHANGE_MASK ((__force upf_t) __UPF_CHANGE_MASK)
#define UPF_USR_MASK ((__force upf_t) (UPF_SPD_MASK|UPF_LOW_LATENCY))
#if __UPF_CHANGE_MASK > ASYNC_FLAGS
#error Change mask not equivalent to userspace-visible bit defines
#endif
/*
* Must hold termios_rwsem, port mutex and port lock to change;
* can hold any one lock to read.
*/
upstat_t status;
#define UPSTAT_CTS_ENABLE ((__force upstat_t) (1 << 0))
#define UPSTAT_DCD_ENABLE ((__force upstat_t) (1 << 1))
#define UPSTAT_AUTORTS ((__force upstat_t) (1 << 2))
#define UPSTAT_AUTOCTS ((__force upstat_t) (1 << 3))
#define UPSTAT_AUTOXOFF ((__force upstat_t) (1 << 4))
int hw_stopped; /* sw-assisted CTS flow state */
unsigned int mctrl; /* current modem ctrl settings */
unsigned int timeout; /* character-based timeout */
unsigned int type; /* port type */
const struct uart_ops *ops;
unsigned int custom_divisor;
unsigned int line; /* port index */
unsigned int minor;
resource_size_t mapbase; /* for ioremap */
resource_size_t mapsize;
struct device *dev; /* parent device */
unsigned char hub6; /* this should be in the 8250 driver */
unsigned char suspended;
unsigned char irq_wake;
unsigned char unused[2];
struct attribute_group *attr_group; /* port specific attributes */
const struct attribute_group **tty_groups; /* all attributes (serial core use only) */
struct serial_rs485 rs485;
void *private_data; /* generic platform data pointer */
};
// uart 驱动注册
int uart_register_driver(struct uart_driver *uart);
// uart 驱动注销
void uart_unregister_driver(struct uart_driver *uart);
int uart_add_one_port(struct uart_driver *reg, struct uart_port *port);
int uart_remove_one_port(struct uart_driver *reg, struct uart_port *port);
int uart_match_port(struct uart_port *port1, struct uart_port *port2);
* #### 通过实例看一下具体是怎么实现一个完整的 uart 驱动的
```c
// drivers/tty/serial/omap-serial.c
// 在文件最后，还是老套路
module_init(serial_omap_init);
module_exit(serial_omap_exit);
MODULE_DESCRIPTION("OMAP High Speed UART driver");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Texas Instruments Inc");
// 让我们跟到 serial_omap_init
static int __init serial_omap_init(void)
{
int ret;
// uart 驱动注册
ret = uart_register_driver(&serial_omap_reg);
if (ret != 0)
return ret;
// uart 平台驱动注册
ret = platform_driver_register(&serial_omap_driver);
if (ret != 0)
uart_unregister_driver(&serial_omap_reg);
return ret;
}
// serial_omap_reg
static struct uart_driver serial_omap_reg = {
.owner = THIS_MODULE,
.driver_name = "OMAP-SERIAL",
.dev_name = OMAP_SERIAL_NAME,
.nr = OMAP_MAX_HSUART_PORTS,
.cons = OMAP_CONSOLE,
};
// serial_omap_driver
static struct platform_driver serial_omap_driver = {
.probe = serial_omap_probe, // probe 开始函数
.remove = serial_omap_remove,
.driver = {
.name = DRIVER_NAME,
.pm = &serial_omap_dev_pm_ops,
.of_match_table = of_match_ptr(omap_serial_of_match), // of_match_table 匹配函数
},
};
// probe 函数
static int serial_omap_probe(struct platform_device *pdev)
{
struct omap_uart_port_info *omap_up_info = dev_get_platdata(&pdev->dev);
struct uart_omap_port *up;
struct resource *mem;
void __iomem *base;
int uartirq = 0;
int wakeirq = 0;
int ret;
// 获取相关信息
/* The optional wakeirq may be specified in the board dts file */
if (pdev->dev.of_node) {
uartirq = irq_of_parse_and_map(pdev->dev.of_node, 0);
if (!uartirq)
return -EPROBE_DEFER;
wakeirq = irq_of_parse_and_map(pdev->dev.of_node, 1);
omap_up_info = of_get_uart_port_info(&pdev->dev);
pdev->dev.platform_data = omap_up_info;
} else {
uartirq = platform_get_irq(pdev, 0);
if (uartirq < 0)
return -EPROBE_DEFER;
}
up = devm_kzalloc(&pdev->dev, sizeof(*up), GFP_KERNEL);
if (!up)
return -ENOMEM;
// 内存，地址
mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
base = devm_ioremap_resource(&pdev->dev, mem);
if (IS_ERR(base))
return PTR_ERR(base);
up->dev = &pdev->dev;
up->port.dev = &pdev->dev;
up->port.type = PORT_OMAP;
up->port.iotype = UPIO_MEM;
up->port.irq = uartirq;
up->port.regshift = 2;
up->port.fifosize = 64;
up->port.ops = &serial_omap_pops;
if (pdev->dev.of_node) // 获取id
ret = of_alias_get_id(pdev->dev.of_node, "serial");
else
ret = pdev->id;
if (ret < 0) {
dev_err(&pdev->dev, "failed to get alias/pdev id, errno %d\n",
ret);
goto err_port_line;
}
up->port.line = ret;
if (up->port.line >= OMAP_MAX_HSUART_PORTS) {
dev_err(&pdev->dev, "uart ID %d > MAX %d.\n", up->port.line,
OMAP_MAX_HSUART_PORTS);
ret = -ENXIO;
goto err_port_line;
}
up->wakeirq = wakeirq;
if (!up->wakeirq)
dev_info(up->port.dev, "no wakeirq for uart%d\n",
up->port.line);
ret = serial_omap_probe_rs485(up, pdev->dev.of_node);
if (ret < 0)
goto err_rs485;
// 设置相关信息
sprintf(up->name, "OMAP UART%d", up->port.line);
up->port.mapbase = mem->start;
up->port.membase = base;
up->port.flags = omap_up_info->flags;
up->port.uartclk = omap_up_info->uartclk;
up->port.rs485_config = serial_omap_config_rs485;
if (!up->port.uartclk) {
up->port.uartclk = DEFAULT_CLK_SPEED;
dev_warn(&pdev->dev,
"No clock speed specified: using default: %d\n",
DEFAULT_CLK_SPEED);
}
up->latency = PM_QOS_CPU_DMA_LAT_DEFAULT_VALUE;
up->calc_latency = PM_QOS_CPU_DMA_LAT_DEFAULT_VALUE;
pm_qos_add_request(&up->pm_qos_request,
PM_QOS_CPU_DMA_LATENCY, up->latency);
INIT_WORK(&up->qos_work, serial_omap_uart_qos_work);
platform_set_drvdata(pdev, up);
if (omap_up_info->autosuspend_timeout == 0)
omap_up_info->autosuspend_timeout = -1;
device_init_wakeup(up->dev, true);
pm_runtime_use_autosuspend(&pdev->dev);
pm_runtime_set_autosuspend_delay(&pdev->dev,
omap_up_info->autosuspend_timeout);
pm_runtime_irq_safe(&pdev->dev);
pm_runtime_enable(&pdev->dev);
pm_runtime_get_sync(&pdev->dev);
omap_serial_fill_features_erratas(up);
ui[up->port.line] = up;
serial_omap_add_console_port(up);
ret = uart_add_one_port(&serial_omap_reg, &up->port);
if (ret != 0)
goto err_add_port;
pm_runtime_mark_last_busy(up->dev);
pm_runtime_put_autosuspend(up->dev);
// John add. 这个是另外的，不属于原生驱动
#define GPIO_TO_PIN(bank, gpio) (32 * (bank) + (gpio))
devm_gpio_request(up->dev, GPIO_TO_PIN(0,22), "omap-serial");
devm_gpio_request(up->dev, GPIO_TO_PIN(0,23), "omap-serial");
devm_gpio_request(up->dev, GPIO_TO_PIN(0,19), "omap-serial");
devm_gpio_request(up->dev, GPIO_TO_PIN(0,12), "omap-serial");
gpio_direction_output(GPIO_TO_PIN(0,22),1); //COM0_MODE_0=1
gpio_direction_output(GPIO_TO_PIN(0,23),0); //COM0_MODE_1=0
gpio_direction_output(GPIO_TO_PIN(0,19),0); //COM0_TERM=0
gpio_direction_output(GPIO_TO_PIN(0,12),1); //LVDS_BLKT_ON=1
return 0;
err_add_port:
pm_runtime_put(&pdev->dev);
pm_runtime_disable(&pdev->dev);
pm_qos_remove_request(&up->pm_qos_request);
device_init_wakeup(up->dev, false);
err_rs485:
err_port_line:
return ret;
}
看一下 uart_register_driver 内部是怎么实现的
int uart_register_driver(struct uart_driver *drv)
{
struct tty_driver *normal; // 主要是对这个 tty 驱动结构体进行了初始化。
int i, retval;
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 = kzalloc(sizeof(struct uart_state) * drv->nr, GFP_KERNEL);
if (!drv->state)
goto out;
// 申请了一个 tty 驱动结构体
normal = alloc_tty_driver(drv->nr);
if (!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->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
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;
}
// tty 驱动的注册
retval = tty_register_driver(normal);
if (retval >= 0)
return retval;
for (i = 0; i < drv->nr; i++)
tty_port_destroy(&drv->state[i].port);
put_tty_driver(normal);
out_kfree:
kfree(drv->state);
out:
return -ENOMEM;
}
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