技术文章:基于Linux的tty架构及UART驱动详解
2.2.3. struct uart_state
每一个uart端口对应着一个uart_state,该结构体将uart_port与对应的circ_buf联系起来。uart_state有两个成员在底层串口驱动会用到:xmit和port。
用户空间程序通过串口发送数据时,上层驱动将用户数据保存在xmit;而串口发送中断处理函数就是通过xmit获取到用户数据并将它们发送出去。串口接收中断处理函数需要通过port将接收到的数据传递给线路规程层。
struct uart_state {
struct tty_port port;
enum uart_pm_state pm_state;
struct circ_buf xmit;
struct uart_port *uart_port; 对应于一个串口设备
};
2.2.4. struct uart_port
uart_port用于描述串口端口的I/O端口或I/O内存地址、FIFO大小、端口类型、串口时钟等信息。实际上,一个uart_port实现对应一个串口设备。
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);
int (*handle_irq)(struct uart_port *);
void (*pm)(struct uart_port *, unsigned int state,
unsigned int old);
void (*handle_break)(struct uart_port *);
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 (0)
#define UPIO_HUB6 (1)
#define UPIO_MEM (2)
#define UPIO_MEM32 (3)
#define UPIO_AU (4) Au1x00 and RT288x type IO
#define UPIO_TSI (5) Tsi108/109 type IO
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
upf_t flags;
#define UPF_FOURPORT ((__force upf_t) (1 << 1))
#define UPF_SAK ((__force upf_t) (1 << 2))
#define UPF_SPD_MASK ((__force upf_t) (0x1030))
#define UPF_SPD_HI ((__force upf_t) (0x0010))
#define UPF_SPD_VHI ((__force upf_t) (0x0020))
#define UPF_SPD_CUST ((__force upf_t) (0x0030))
#define UPF_SPD_SHI ((__force upf_t) (0x1000))
#define UPF_SPD_WARP ((__force upf_t) (0x1010))
#define UPF_SKIP_TEST ((__force upf_t) (1 << 6))
#define UPF_AUTO_IRQ ((__force upf_t) (1 << 7))
#define UPF_HARDPPS_CD ((__force upf_t) (1 << 11))
#define UPF_LOW_LATENCY ((__force upf_t) (1 << 13))
#define UPF_BUGGY_UART ((__force upf_t) (1 << 14))
#define UPF_NO_TXEN_TEST ((__force upf_t) (1 << 15))
#define UPF_MAGIC_MULTIPLIER ((__force upf_t) (1 << 16))
Port has hardware-assisted h/w flow control (iow, auto-RTS *not* auto-CTS)
#define UPF_HARD_FLOW ((__force upf_t) (1 << 21))
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 ((__force upf_t) (0x17fff))
#define UPF_USR_MASK ((__force upf_t) (UPF_SPD_MASK|UPF_LOW_LATENCY))
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
resource_size_t mapbase; for ioremap
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];
void *private_data; generic platform data pointer
};
2.2.5. struct uart_ops
struct uart_ops涵盖了驱动可对串口的所有操作
struct uart_ops {
unsigned int (*tx_empty)(struct uart_port *);
void (*set_mctrl)(struct uart_port *, unsigned int mctrl);
unsigned int (*get_mctrl)(struct uart_port *);
void (*stop_tx)(struct uart_port *);
void (*start_tx)(struct uart_port *);
void (*throttle)(struct uart_port *);
void (*unthrottle)(struct uart_port *);
void (*send_xchar)(struct uart_port *, char ch);
void (*stop_rx)(struct uart_port *);
void (*enable_ms)(struct uart_port *);
void (*break_ctl)(struct uart_port *, int ctl);
int (*startup)(struct uart_port *);
void (*shutdown)(struct uart_port *);
void (*flush_buffer)(struct uart_port *);
void (*set_termios)(struct uart_port *, struct ktermios *new,
struct ktermios *old);
void (*set_ldisc)(struct uart_port *, int new);
void (*pm)(struct uart_port *, unsigned int state,
unsigned int oldstate);
int (*set_wake)(struct uart_port *, unsigned int state);
* Return a string describing the type of the port
const char *(*type)(struct uart_port *);
* Release IO and memory resources used by the port.
* This includes iounmap if necessary.
void (*release_port)(struct uart_port *);
* Request IO and memory resources used by the port.
* This includes iomapping the port if necessary.
int (*request_port)(struct uart_port *);
void (*config_port)(struct uart_port *, int);
int (*verify_port)(struct uart_port *, struct serial_struct *);
int (*ioctl)(struct uart_port *, unsigned int, unsigned long);
#ifdef CONFIG_CONSOLE_POLL
int (*poll_init)(struct uart_port *);
void (*poll_put_char)(struct uart_port *, unsigned char);
int (*poll_get_char)(struct uart_port *);
#endif
};
2.3. 关键流程2.3.1. 注册流程2.3.1.1. 注册uart_driver
此接口在uart driver中调用,用来注册uart_driver到kernel中,调用阶段在uart driver的初始阶段,例如:module_init(), uart_driver的注册流程图
图3.3uart driver注册流程
注册过程主要做了以下操作:
1、根据driver支持的最大设备数,申请n个uart_state空间,每一个uart_state都有一个uart_port。2、分配一个tty_driver,并将uart_driver->tty_driver指向它。3、对tty_driver进行设置,其中包括默认波特率、检验方式等,还有一个重要的ops,结构体tty_operation的注册,它是tty核心与串口驱动通信的接口。4、初始化每一个uart_state的tty_port;5、注册tty_driver。注册uart_driver实际上是注册tty_driver,与用户空间打交道的工作完全交给tty_driver,这一部分是内核实现好的不需要修改2.3.1.2. 添加uart_port
此接口用于注册一个uart port 到uart driver上,通过注册,uart driver就可以访问对应的uart port,进行数据收发。该接口在uart driver中的probe函数调用,必须保证晚于uart_register_drver的注册过程。
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