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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。
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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。
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kernel version 4.4.12
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首先先看一下基本的 结构体 和 API 操作。
// 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 intuart_register_driver(struct uart_driver *uart); // uart 驱动注销 voiduart_unregister_driver(struct uart_driver *uart); intuart_add_one_port(struct uart_driver *reg, struct uart_port *port); intuart_remove_one_port(struct uart_driver *reg, struct uart_port *port); intuart_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
// 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; }
时间： 2024-11-01 21:21:49