linux内核在sTc上移值,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;

u32num_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 semaphoresem;/* 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_infopower;

#ifdef CONFIG_NUMA

intnuma_node;/* NUMA node this device is close to */

#endif

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

u64coherent_dma_mask;

struct device_dma_parameters *dma_parms;

struct list_headdma_pools;/* dma pools (if dma'ble) */

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

struct dev_archdataarchdata; /* arch specific additions */

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

spinlock_tdevres_lock;

struct list_headdevres_head;

struct klist_nodeknode_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 %sabledn", 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 Driversà

Character Devicesà

Serial Driversà

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,

}