linux设备驱动之8250串口驱动.docx

1、linux设备驱动之8250串口驱动linux设备驱动之8250串口驱动一：前言 前一段时间自己实践了一下8250芯片串口驱动的编写。今天就在此基础上分析一下linux kernel自带的串口驱动。毕竟只有对比专业的驱动代码才能更好的进步,同以往一样，基于linix kernel2.6.25.相应驱动代码位于：linux-2.6.25/drivers/serial/8250.c。 二：8250串口驱动初始化 相应的初始化函数为serial8250_init().代码如下: static int _init serial8250_init(void) int ret, i; if (nr_uar

2、ts UART_NR) nr_uarts = UART_NR; printk(KERN_INFO Serial: 8250/16550 driver $Revision: 1.90 $ %d ports, IRQ sharing %sabledn, nr_uarts, share_irqs ? en : dis); for (i = 0; i dev); ret = platform_driver_register(&serial8250_isa_driver); if (ret = 0) goto out; platform_device_del(serial8250_isa_devs);

3、put_dev: platform_device_put(serial8250_isa_devs); unreg_uart_drv: uart_unregister_driver(&serial8250_reg); out: return ret; 这段代码涉及到的知识要求，如platform ,uart等我们在之前都已经做过详细的分析。这里不再重复。在代码中UART_NR:表示串口的个数。这个参数在编译内核的时候可以自己配置，默认为32。 我们按照代码中的流程一步一步进行研究。 1：注册uart_driver. 对应uart-driver的结构为serial8250_reg.定义如下： st

4、atic struct uart_driver serial8250_reg = .owner = THIS_MODULE, .driver_name = serial, .dev_name = ttyS, .major = TTY_MAJOR, .minor = 64, .nr = UART_NR, .cons = SERIAL8250_CONSOLE, ; TTY_MAJOR定义如下： #define TTY_MAJOR 4 从上面可以看出。串口对应的设备节点为/dev/ ttyS0 /dev/ ttyS0(UART_NR).设备节点号为（4。64）起始的UART_NR个节点. 2:初始化

5、并注册platform_device 相关代码如下： serial8250_isa_devs = platform_device_alloc(serial8250, PAT8250_DEV_LEGACY); platform_device_add(serial8250_isa_devs); 可以看出。serial8250_isa_devs.-name为serial8250。这个参数是在匹配platform_device和platform_driver使用的. 3:为uart-driver添加port. 相关代码如下： serial8250_register_ports(&serial8250_

6、reg, &serial8250_isa_devs-dev) 跟进这个函数看一下： static void _init serial8250_register_ports(struct uart_driver *drv, struct device *dev) int i; serial8250_isa_init_ports(); for (i = 0; i port.dev = dev; uart_add_one_port(drv, &up-port); 在这里函数里，初始化了port.然后将挂添加到uart-driver中。我们还注意到。生成的deivce节点，在sysfs中是位于plat

7、form_deivce对应目录的下面. serial8250_isa_init_ports()代码如下所示： static void _init serial8250_isa_init_ports(void) struct uart_8250_port *up; static int first = 1; int i; if (!first) return; first = 0; for (i = 0; i port.line = i; spin_lock_init(&up-port.lock); init_timer(&up-timer); up-timer.function = seria

8、l8250_timeout; /* * ALPHA_KLUDGE_MCR needs to be killed. */ 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 port.iobase = old_serial_porti.port; up-port.irq = irq_canonicalize(old_se

9、rial_porti.irq); up-port.uartclk = old_serial_porti.baud_base * 16; up-port.flags = old_serial_porti.flags; up-port.hub6 = old_serial_porti.hub6; up-port.membase = old_serial_porti.iomem_base; up-port.iotype = old_serial_porti.io_type; up-port.regshift = old_serial_porti.iomem_reg_shift; if (share_i

10、rqs) up-port.flags |= UPF_SHARE_IRQ; 在这里，我们关注一下注要成员的初始化。Uart_port的各项操作位于serial8250_pops中.iobase irq等成员是从old_serial_por这个结构中得来的，这个结构如下所示： static const struct old_serial_port old_serial_port = SERIAL_PORT_DFNS /* defined in asm/serial.h */ #define SERIAL_PORT_DFNS /* UART CLK PORT IRQ FLAGS */ 0, BASE

11、_BAUD, 0x3F8, 4, STD_COM_FLAGS , /* ttyS0 */ 0, BASE_BAUD, 0x2F8, 3, STD_COM_FLAGS , /* ttyS1 */ 0, BASE_BAUD, 0x3E8, 4, STD_COM_FLAGS , /* ttyS2 */ 0, BASE_BAUD, 0x2E8, 3, STD_COM4_FLAGS , /* ttyS3 */ 从上面看到。前两项对应了com1 com2的各项参数。如寄存器首始地址，Irq号等。后面两项不太清楚。 在上面的代码中，我们看到了uart_port各项成员的初始化。在后面很多操作中需要用到这个成

12、员。我们等分析相关部份的时候，再到这个地方来看相关成员的值。 4:注册platform_driver 相关代码如下： platform_driver_register(&serial8250_isa_driver); serial8250_isa_driver定义如下: static struct platform_driver serial8250_isa_driver = .probe = serial8250_probe, .remove = _devexit_p(serial8250_remove), .suspend = serial8250_suspend, .resume = s

13、erial8250_resume, .driver = .name = serial8250, .owner = THIS_MODULE, , 为了以后把分析集中到具体的驱动部份.我们先把这个platform_driver引会的事件讲述完. 经过前面有关platform的分析我们知道.这个platform的name为” serial8250”.刚好跟前面注册的platform_device相匹配.会调用platform_driver- probe.在这里,对应的接口为: serial8250_probe().代码如下: static int _devinit serial8250_probe(

14、struct platform_device *dev) struct plat_serial8250_port *p = dev-dev.platform_data; struct uart_port port; int ret, i; memset(&port, 0, sizeof(struct uart_port); for (i = 0; p & p-flags != 0; p+, i+) port.iobase = p-iobase; port.membase = p-membase; port.irq = p-irq; port.uartclk = p-uartclk; port.

15、regshift = p-regshift; port.iotype = p-iotype; port.flags = p-flags; port.mapbase = p-mapbase; port.hub6 = p-hub6; port.private_data = p-private_data; port.dev = &dev-dev; if (share_irqs) port.flags |= UPF_SHARE_IRQ; ret = serial8250_register_port(&port); if (ret dev, unable to register port at inde

16、x %d (IO%lx MEM%llx IRQ%d): %dn, i, p-iobase, (unsigned long long)p-mapbase, p-irq, ret); return 0; 从上述代码可以看出.会将dev-dev.platform_data所代表的port添加到uart_driver中.这个dev-dev.platform_data究竟代表什么.我们在看到的时候再来研究它. 现在,我们把精力集中到uart_port的操作上. 三:config_port过程 在初始化uart_port的过程中,在以下代码片段: serial8250_isa_init_ports(voi

17、d) for (i = 0, up = serial8250_ports; i ARRAY_SIZE(old_serial_port) & i port.iobase = old_serial_porti.port; up-port.irq = irq_canonicalize(old_serial_porti.irq); up-port.uartclk = old_serial_porti.baud_base * 16; up-port.flags = old_serial_porti.flags; up-port.hub6 = old_serial_porti.hub6; up-port.

18、membase = old_serial_porti.iomem_base; up-port.iotype = old_serial_porti.io_type; up-port.regshift = old_serial_porti.iomem_reg_shift; if (share_irqs) up-port.flags |= UPF_SHARE_IRQ; 而old_serial_port又定义如下: static const struct old_serial_port old_serial_port = SERIAL_PORT_DFNS /* defined in asm/seria

19、l.h */ ; #define SERIAL_PORT_DFNS /* UART CLK PORT IRQ FLAGS */ 0, BASE_BAUD, 0x3F8, 4, STD_COM_FLAGS , /* ttyS0 */ 0, BASE_BAUD, 0x2F8, 3, STD_COM_FLAGS , /* ttyS1 */ 0, BASE_BAUD, 0x3E8, 4, STD_COM_FLAGS , /* ttyS2 */ 0, BASE_BAUD, 0x2E8, 3, STD_COM4_FLAGS , /* ttyS3 */ 由此可见.port-flags被定义成了STD_COM

20、_FLAGS,定义如下: #ifdef CONFIG_SERIAL_DETECT_IRQ #define STD_COM_FLAGS (ASYNC_BOOT_AUTOCONF | ASYNC_SKIP_TEST | ASYNC_AUTO_IRQ) #define STD_COM4_FLAGS (ASYNC_BOOT_AUTOCONF | ASYNC_AUTO_IRQ) #else #define STD_COM_FLAGS (ASYNC_BOOT_AUTOCONF | ASYNC_SKIP_TEST) #define STD_COM4_FLAGS ASYNC_BOOT_AUTOCONF #en

21、dif 从这里看到,不管是否自己探测IRQ,都会定义ASYNC_BOOT_AUTOCONF.这样,在uart_add_one_port()的时候.就会进入到port-config_port来配置端口.在8250中,对应的接口为: serial8250_config_port().代码如下: static void serial8250_config_port(struct uart_port *port, int flags) struct uart_8250_port *up = (struct uart_8250_port *)port; int probeflags = PROBE_AN

22、Y; int ret; /* * Find the region that we can probe for. This in turn * tells us whether we can probe for the type of port. */ ret = serial8250_request_std_resource(up); if (ret 0) return; ret = serial8250_request_rsa_resource(up); if (ret port.type != PORT_UNKNOWN & flags & UART_CONFIG_IRQ) autoconf

23、ig_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); serial8250_request_std_resource和serial8250_request_rsa_resource都是分配操作的端口.回顾在前面的分析中.port的相关参数会从old_serial_port中取得.而old_serial_p

24、ort中又没有定义port-iotype和port- regshift.也就是说对应这两项全为0.而 #define UPIO_PORT (0) 即表示是要操作I/O端口. 自己阅读这两个函数代表.会发现在serial8250_request_rsa_resource()中是会返回失败的. 另外,在uart_add_one_port()在进行端口匹配时,会先置flags为UART_CONFIG_TYPE. 这样,在本次操作中, if (flags & UART_CONFIG_TYPE)是会满足的.相应的就会进入autoconfig(). 代码如下,这段代码比较长,分段分析如下: static

25、void autoconfig(struct uart_8250_port *up, unsigned int probeflags) unsigned char status1, scratch, scratch2, scratch3; unsigned char save_lcr, save_mcr; unsigned long flags; if (!up-port.iobase & !up-port.mapbase & !up-port.membase) return; DEBUG_AUTOCONF(ttyS%d: autoconf (0x%04x, 0x%p): , up-port.

26、line, up-port.iobase, up-port.membase); /* * We really do need global IRQs disabled here - were going to * be frobbing the chips IRQ enable register to see if it exists. */ spin_lock_irqsave(&up-port.lock, flags); up-capabilities = 0; up-bugs = 0; if (!(up-port.flags & UPF_BUGGY_UART) /* * Do a simp

27、le existence test first; if we fail this, * theres no point trying anything else. * * 0x80 is used as a nonsense port to prevent against * false positives due to ISA bus float. The * assumption is that 0x80 is a non-existent port; * which should be safe since include/asm/io.h also * makes this assumption. * * Note: this is safe as long as MCR bit 4 is clear * and the device is in PC