我在Linux-2.6.32.2下为ST16C554移植驱动的经历

一、Linux 驱动的基本理论

    理解linux驱动，最重要的是要区分device和driver这两个概念,要搞清device和driver之间的联系。 device 描述了某个设备所占用的硬件资源（地址、中断），可以理解为硬件方面描述。而driver则是描述了使用和操作该设备的方法、流程、逻辑，可以理解为软件方面的描述。这二者之间的对应联系是一个设备名。

我们来看一下两个结构体的定义：

struct platform_device {

       const char* name; /* 连接device和driver的名字，系统内唯一！*/

      int id;

      struct device dev;

      u32  num_resources;

      struct resource * resource;

      struct platform_device_id * id_entry;

      struct pdev_archdata archdata;

};

在arch/arm/mach-s3c2440/mach-mini2440.c中初始化

struct device {

      struct device          *parent;

      struct device_private      *p;

      struct kobject kobj;

      const char              *init_name; /* initial name of the device */

      struct device_type   *type;

      struct semaphore    sem; /* semaphore to synchronize calls to its driver. */

      struct bus_type       *bus;              /* type of bus device is on */

      struct device_driver *driver;  /* which driver has allocated this device */

      void        *platform_data;      /* Platform specific data, device core doesn't touch it */

      struct dev_pm_info power;

#ifdef CONFIG_NUMA

      int          numa_node;    /* NUMA node this device is close to */

#endif

      u64         *dma_mask;   /* dma mask (if dma'able device) */

      u64         coherent_dma_mask;

      struct device_dma_parameters *dma_parms;

      struct list_head       dma_pools;     /* dma pools (if dma'ble) */

      struct dma_coherent_mem     *dma_mem; /* internal for coherent mem override */

      struct dev_archdata archdata; /* arch specific additions */

      dev_t      devt;              /* dev_t, creates the sysfs "dev" */

      spinlock_t              devres_lock;

      struct list_head       devres_head;

      struct klist_node     knode_class;

      struct class             *class;

      const struct attribute_group **groups;  /* optional groups */

      void (*release)(struct device *dev);

};

       struct platform_driver {

              int (*probe)(struct platform_device *);

              int (*remove)(struct platform_device *);

              void (*shutdown)(struct platform_device *);

              int (*suspend)(struct platform_device *, pm_message_t state);

              int (*resume)(struct platform_device *);

              struct device_driver driver;

              struct platform_device_id *id_table;

};

在drivers/serial/8250.c中初始化

struct device_driver {

       const char *name;  /* 连接device和driver的名字，系统内唯一！*/

       struct bus_type *bus;

       struct module  *owner;

       const char *mod_name;  /* used for built-in modules */

       bool suppress_bind_attrs;      /* disables bind/unbind via sysfs */

       int (*probe) (struct device *dev);

       int (*remove) (struct device *dev);

       void (*shutdown) (struct device *dev);

       int (*suspend) (struct device *dev, pm_message_t state);

       int (*resume) (struct device *dev);

       const struct attribute_group **groups;

       const struct dev_pm_ops *pm;

       struct driver_private *p;

};

 

二、ST16C554

    st16c554是一款集成了4路标准异步串行收发器的串口扩展芯片，也就是通常所说的16c550（也同8250）适应串口。可以将其看成是简单封装了4个16c550的芯片。它的操作方法和寄存器用法与8250完全相同，因此我们可以用linux内经典的8250驱动来驱动st16c554。

 

三、移植过程

       硬件平台：mini2440    系统：linux-2.6.32.2

       红色部分为添加的语句。

1.       修改arch/arm/mach-s3c2440/mach-mini2440.c

添加头文件

#ifdef CONFIG_SERIAL_8250_MINI2440_ST16C554

#include

#endif

初始化st16c554的platform_device数据结构

/* STC16c554 Extend Quad Uarts */

#define PORT(_base,_irq)                           \

{ //ARM体系结构中将IO和MEMORY统一编址，

     //因此这里使用的是Memory地址                    

        .mapbase = (unsigned long)_base,    \

        .irq                = _irq,                  \

        .uartclk          = 1843200,            \

        .iotype           = UPIO_MEM32,         \

        .flags             = (UPF_BOOT_AUTOCONF | UPF_IOREMAP),      \

        .regshift         = 0, \

}

static struct plat_serial8250_port mini2440_st16c554_8250_data[] = {

       PORT(S3C2410_CS1 + 0x0, IRQ_EINT0),

       PORT(S3C2410_CS2 + 0x0, IRQ_EINT1),

       PORT(S3C2410_CS3 + 0x0, IRQ_EINT2),

       PORT(S3C2410_CS5 + 0x0, IRQ_EINT3),

       { },

};

static struct platform_device mini2440_device_st16c554 = {

     .name             = "serial8250",

     .id                 = PLAT8250_DEV_EXAR_ST16C554,

     .dev               = {

            .platform_data       = &mini2440_st16c554_8250_data,

     },

};

将st16c554对应的platform_device数据结构体添加到mini2440对应的platform_device数据结构体中。

/* devices we initialise */

static struct platform_device *mini2440_devices[] __initdata = {

&s3c_device_usb,

&s3c_device_rtc,

&s3c_device_lcd,

&s3c_device_wdt,

&s3c_device_i2c0,

&s3c_device_iis,

&mini2440_device_eth,

//#ifdef CONFIG_SERIAL_8250_MINI2440_ST16C554

&mini2440_device_st16c554,

//#endif

&s3c24xx_uda134x,

&s3c_device_nand,

&s3c_device_sdi,

&s3c_device_usbgadget,

};

2．修改 drivers/serial/8250.c

       添加头文件

#ifdef CONFIG_SERIAL_8250_MINI2440_ST16C554

#include

#endif

 

修改S3C2440 四个Bank使用的的 bus width为8位，以及设定这四个Bank的总线 timing。

static int __init serial8250_init(void)

{

       int ret;

       if (nr_uarts > UART_NR)

              nr_uarts = UART_NR;

       printk(KERN_INFO "Serial: 8250/16550 driver, "

              "%d ports, IRQ sharing %sabled\n", nr_uarts,

              share_irqs ? "en" : "dis");

#ifdef CONFIG_SERIAL_8250_MINI2440_ST16C554

       /* Set the 8bit bus width of bank1,bank2,bank3,bank5*/

       *((volatile unsigned int *)S3C2410_BWSCON) =

((*((volatile unsigned int *)S3C2410_BWSCON)) & ~(0x30333<<4))

                            | S3C2410_BWSCON_DW1_8

                            | S3C2410_BWSCON_DW2_8

                            | S3C2410_BWSCON_DW3_8

                            | S3C2410_BWSCON_DW5_8;

       /* Set the interface timing between s3c2440 and st16c554 */

       //     *((volatile unsigned int *)S3C2410_BANKCON1) = 0x1f7c;

       //     *((volatile unsigned int *)S3C2410_BANKCON2) = 0x1f7c;    

       //     *((volatile unsigned int *)S3C2410_BANKCON3) = 0x1f7c;

       //     *((volatile unsigned int *)S3C2410_BANKCON5) = 0x1f7c;

#endif

#ifdef CONFIG_SPARC

       ret = sunserial_register_minors(&serial8250_reg, UART_NR);

#else

       serial8250_reg.nr = UART_NR;

       ret = uart_register_driver(&serial8250_reg);

#endif

       if (ret)

              goto out;

#ifdef CONFIG_8250_MINI2440_ST16C554

serial8250_isa_devs =

platform_device_alloc("serial8250", PLAT8250_DEV_EXAR_ST16C554);

#else

       serial8250_isa_devs = platform_device_alloc("serial8250",

                                              PLAT8250_DEV_LEGACY);

#endif

修改中断信号的类型为下降沿触发

       if (i->head) {

              list_add(&up->list, i->head);

              spin_unlock_irq(&i->lock);

              ret = 0;

       } else {

              INIT_LIST_HEAD(&up->list);

              i->head = &up->list;

              spin_unlock_irq(&i->lock);

#ifdef CONFIG_SERIAL_8250_MINI2440_ST16C554

              irq_flags |= IRQF_TRIGGER_RISING;

#else

              irq_flags |= up->port.irqflags;

#endif

              ret = request_irq(up->port.irq, serial8250_interrupt,

                              irq_flags, "serial", i);

              if (ret < 0)

                     serial_do_unlink(i, up);

       }

3．修改 drivers/serial/Kconfig

添加一个编译配置选项

config SERIAL_8250_MINI2440_ST16C554

       bool "Support MINI2440 Extend ST16C554/554D Quad UART"

       depends on SERIAL_8250

       help

         A chip of ST16C554 is uesed to extend Quad UART on the MINI2440 Board.  If you are tinkering with ST16C554, or have a machine with this UART, say Y here.

To compile this driver as a module, choose M here: the module will be called 8250_mini2440_st16c554.

 

4．重新编译内核

> make menucofig

Device Drivers  à

       Character Devices  à

                     Serial Drivers  à

               <*> 8250/16c550 and compatible serial support

                            [*] Support MINI2440 Extend ST16C554/554D Quad UART

保存.config文件

> make zImage

 

这样驱动就添加好了，如果你的根文件系统使用了mdev，那么不用做任何修改，mdev会自动地将四个新串口添加在 /dev/serial/tty目录下面，分别为 ttyS0, ttyS1, ttyS2, ttyS3。

查看更详细的信息

> cat /proc/tty/driver/serial 将显示四个串口的物理地址和虚拟地址

 

四．碰到的问题

内核启动过程中，报错

Unable to handle kernel NULL pointer dereference at virtual address 000000c0

产生这个错误有两种可能：

（1）       地址指针错误，比如在初始化平台设备结构体时丢掉了&符号。

static struct platform_device mini2440_device_st16c554 = {

     .name             = "serial8250",

     .id                 = PLAT8250_DEV_EXAR_ST16C554,

     .dev               = {

            .platform_data       = &mini2440_st16c554_8250_data,

     },

};

（2）       在为ST16C554的四个端口指定系统地址时，没有使用Memory地址，而使用了IO地址。

#define PORT(_base,_irq)                           \

{                                                             \

        .mapbase        = (unsigned long)_base, \

        .irq                = _irq,                  \

        .uartclk          = 1843200,            \

        .iotype           = UPIO_MEM32,         \

        .flags             = (UPF_BOOT_AUTOCONF | UPF_IOREMAP),      \

        .regshift         = 0, \

}

在 driver/serial/8250_exar_st16c554.c中使用的是IO地址

#define PORT(_base,_irq)                          \

       {                                        \

              .iobase    = _base,         \

              .irq         = _irq,                  \

              .uartclk   = 1843200,            \

              .iotype    = UPIO_PORT,             \

              .flags      = UPF_BOOT_AUTOCONF,       \

       }