基于Mips架构linux下设备树串口驱动(二)

本设备树串口驱动基于linux3.0.4内核版本

serial8250_console_init()

从serial8250_console_init()函数实体开始，追踪分析标准设备驱动流程。函数原型如下，函数实体路径见./drivers/tty/serial/8250.c。可以看出该函数第一次初始化port,第二次注册
console驱动。

static int __init serial8250_console_init(void)
{
 if (nr_uarts > UART_NR)
  nr_uarts = UART_NR;
  
 serial8250_isa_init_ports();
 
 register_console(&serial8250_console);
 return 0;
}
console_initcall(serial8250_console_init);

serial8250_isa_init_ports()

继续追踪函数实体serial8250_isa_init_ports()实现，函数原型如下，函数路径见
./drivers/tty/serial/8250.c。博主主要关主两个for循环内的操作。第一个for循环功能是
初始化定时器功能函数up->timer.function = serial8250_timeout;初始化serial8250 port的操作函数 up->port.ops = &serial8250_pops;这个接口serial8250_pops内有关于port操作函数挂载。第二个for循环功能是初始化默认port硬件参数old_serial_port[i].port;

static void __init serial8250_isa_init_ports(void)
{
	 .................................
	 for (i = 0; i < nr_uarts; i++) {
	  struct uart_8250_port *up = &serial8250_ports[i];
	  up->port.line = i;
	  spin_lock_init(&up->port.lock);
	  init_timer(&up->timer);
	  up->timer.function = serial8250_timeout;
	  up->mcr_mask = ~ALPHA_KLUDGE_MCR;
	  up->mcr_force = ALPHA_KLUDGE_MCR;
	  up->port.ops = &serial8250_pops;
	 }
	 .................................
	 for (i = 0, up = serial8250_ports;
	      i < ARRAY_SIZE(old_serial_port) && i < nr_uarts;
	      i++, up++) {
	  up->port.iobase   = old_serial_port[i].port;
	  up->port.irq      = irq_canonicalize(old_serial_port[i].irq);
	  up->port.irqflags = old_serial_port[i].irqflags;
	  up->port.uartclk  = old_serial_port[i].baud_base * 16;
	  up->port.flags    = old_serial_port[i].flags;
	  up->port.hub6     = old_serial_port[i].hub6;
	  up->port.membase  = old_serial_port[i].iomem_base;
	  up->port.iotype   = old_serial_port[i].io_type;
	  up->port.regshift = old_serial_port[i].iomem_reg_shift;
	  set_io_from_upio(&up->port);
	  up->port.irqflags |= irqflag;
	  if (serial8250_isa_config != NULL)
	   serial8250_isa_config(i, &up->port, &up->capabilities);
	 }
	 .................................
	}

接下来，先分析第一个for循环 up->port.ops = &serial8250_pops;有关于定时器初始化本文不作赘述。函数原型如下，函数实体路径见./drivers/tty/serial/8250.c，重点分析结构体struct uart_ops成员变量.config_port = serial8250_config_port,这是个关于port与硬件配置相关的函数。

static struct uart_ops serial8250_pops = {
 .tx_empty = serial8250_tx_empty,
 .set_mctrl = serial8250_set_mctrl,
 .get_mctrl = serial8250_get_mctrl,
 .stop_tx = serial8250_stop_tx,
 .start_tx = serial8250_start_tx,
 .stop_rx = serial8250_stop_rx,
 .enable_ms = serial8250_enable_ms,
 .break_ctl = serial8250_break_ctl,
 .startup = serial8250_startup,
 .shutdown = serial8250_shutdown,
 .set_termios = serial8250_set_termios,
 .set_ldisc = serial8250_set_ldisc,
 .pm  = serial8250_pm,
 .type  = serial8250_type,
 .release_port = serial8250_release_port,
 .request_port = serial8250_request_port,
 .config_port = serial8250_config_port,
 .verify_port = serial8250_verify_port,
#ifdef CONFIG_CONSOLE_POLL
 .poll_get_char = serial8250_get_poll_char,
 .poll_put_char = serial8250_put_poll_char,
#endif
};

再分析第二个for循环函数，结构体struct old_serial_port默认初始值是串口号，串口波特率，串口时钟频率，串口中断号，以及flags。结合下方第二段代码段图例展示struct old_serial_port定义的内容初始值，思路就逐渐清晰了。而SERIAL_PORT_DFNS宏定义由开发者自行针对硬件平台进行设计，下方只是博主列出一个示例应用。

#define SERIAL_PORT_DFNS      \
       /* UART  CLK     PORT   IRQ            FLAGS */   \
 { 0, BASE_BAUD, 0x3F8, PLD_IRQ_UART0, STD_COM_FLAGS }, /* ttyS0 */ \
 { 0, BASE_BAUD, 0x2F8, PLD_IRQ_UART1, STD_COM_FLAGS }, /* ttyS1 */
 
static const struct old_serial_port old_serial_port[] = {
 SERIAL_PORT_DFNS /* defined in asm/serial.h */
};

struct old_serial_port定义如下，路径见./drivers/tty/serial/8250.h

struct old_serial_port {
 unsigned int uart;
 unsigned int baud_base;
 unsigned int port;
 unsigned int irq;
 unsigned int flags;
 unsigned char hub6;
 unsigned char io_type;
 unsigned char *iomem_base;
 unsigned short iomem_reg_shift;
 unsigned long irqflags;
};

serial8250_config_port()

现在我们回到.config_port = serial8250_config_port,继续追踪分析, 函数实体原型如下，函数路径见./drivers/tty/serial/8250.c，此函数本文只分析介绍三个子函数实现，分别为serial8250_request_std_resource()，serial8250_release_std_resource(),autoconfig()
其它函数本文不作赘述，第一个函数功能是将port的物理地址获取到转换成虚拟地址,类似于ioremap函数。第二个函数与之相反是取消port地址映射，类似于iounmap函数。第三个函树博主续追踪一下其实现。

static void serial8250_config_port(struct uart_port *port, int flags)
{
 struct uart_8250_port *up =
  container_of(port, struct uart_8250_port, port);
 int probeflags = PROBE_ANY;
 int ret;
 ret = serial8250_request_std_resource(up);
 if (ret < 0)
  return;
 ret = serial8250_request_rsa_resource(up);
 if (ret < 0)
  probeflags &= ~PROBE_RSA;
 if (up->port.iotype != up->cur_iotype)
  set_io_from_upio(port);
 if (flags & UART_CONFIG_TYPE)
  autoconfig(up, probeflags);
 /* if access method is AU, it is a 16550 with a quirk */
 if (up->port.type == PORT_16550A && up->port.iotype == UPIO_AU)
  up->bugs |= UART_BUG_NOMSR;
 if (up->port.type != PORT_UNKNOWN && flags & UART_CONFIG_IRQ)
  autoconfig_irq(up);
 if (up->port.type != PORT_RSA && probeflags & PROBE_RSA)
  serial8250_release_rsa_resource(up);
 if (up->port.type == PORT_UNKNOWN)
  serial8250_release_std_resource(up);
}

autoconfig()

继续追踪函数实体autoconfig()，函数原型如下，函数路径见./drivers/tty/serial/8250.c
，此函数主要实现关于硬件参数读取写入操作，此处不作赘述，重点关注UART_IIR值获取到后进行不同类型的串口驱动适配注册。

static void autoconfig(struct uart_8250_port *up, unsigned int probeflags)
{
	................................
	 scratch = serial_in(up, UART_IIR) >> 6;
	 DEBUG_AUTOCONF("iir=%d ", scratch);
	 switch (scratch) {
	 case 0:
	  autoconfig_8250(up);
	  break;
	 case 1:
	  up->port.type = PORT_UNKNOWN;
	  break;
	 case 2:
	  up->port.type = PORT_16550;
	  break;
	 case 3:
	  autoconfig_16550a(up);
	  break;
	 }
	 ................................
}

serial8250_console()

继续追踪serial8250_console()实现，函数原型如下，函数路径见./drivers/tty/serial/8250.c
，此结构体是第一步是cosole基本操作初始化接口，将uart驱动绑定到cosole驱动内。
.data = &serial8250_reg

static struct console serial8250_console = {
 .name  = "ttyS",
 .write  = serial8250_console_write,
 .device  = uart_console_device,
 .setup  = serial8250_console_setup,
 .early_setup = serial8250_console_early_setup,
 .flags  = CON_PRINTBUFFER | CON_ANYTIME,
 .index  = -1,
 .data  = &serial8250_reg,
};

至此底层硬件操作接口注册分析完成，小结如下:
第一步初始化serial8250底层操作函数接口，将serial8250操作函数绑定到uart驱动中。
up->port.ops = &serial8250_pops;
第二步初始化console用户层操作函数接口，将uart驱动操作函数绑定到console驱动中。
.data  = &serial8250_reg,