Linux 2.6下SPI设备模型
--------基于AT91RM9200分析
Atmel公司的ARM AT系列，其SPI驱动在kernel 2.6.23里已经包含。如果你打了at91-patch补丁的话，则在内核配置时要小心。在Device Drivers---- > Character devices ---- >取消选中SPI Driver(legacy) for at91rm9200 processor 。同时Device Drivers---- >SPI Support ---- > 选中SPI Support ,Atmel SPI Controler,同时选中 User mode SPI device driver support 。
SPI Driver(legacy) for at91rm9200 processor是保留选项，为了兼容以前版本。如果同时选中SPI Driver(legacy) for at91rm9200 processor，则在/sys里无法注册类spidev，也就无法将设备和驱动联系在一起。与现有atmel spi驱动发生冲突。
各选项对应的编译情况如下：
[*]SPI support ---- Config_SPI 开启SPI功能
[*]Debug support for SPI drivers ---- config SPI_DEBUG 开启SPI debug调试
----SPI Master Controller Drivers ---- depends on SPI_MASTER 生成spi.o
<*>Atmel SPI Controller ---- config SPI_ATMEL 生成atmel_spi.o
<*>Bitbanging SPI master ---- config SPI_BITBANG 生成spi_bitbang.o
<*>AT91RM9200 Bitbang SPI Master ---- CONFIG_SPI_AT91 spi_at91_bitbang.o
---- SPI Protocol Masters ---- depends on SPI_MASTER
< >SPI EEPROMs from most vendors ---- config SPI_AT25 生成at25.o
<*>User mode SPI device driver support ---- config SPI_SPIDEV 生成spidev.o
总线
注册SPI总线
#spi.c
struct bus_type spi_bus_type = {
.name = "spi", // spi总线名称
.dev_attrs = spi_dev_attrs,
.match = spi_match_device,
.uevent = spi_uevent,
.suspend = spi_suspend,
.resume = spi_resume,
};
spi总线将在sysfs/bus下显示。
其bus_type 结构表示总线，它的定义在<linux/device.h>中，如下
struct bus_type {
const char * name;
struct module * owner;
struct kset subsys;
struct kset drivers;
struct kset devices;
struct klist klist_devices;
struct klist klist_drivers;
struct blocking_notifier_head bus_notifier;
struct bus_attribute * bus_attrs;
struct device_attribute * dev_attrs;
struct driver_attribute * drv_attrs;
struct bus_attribute drivers_autoprobe_attr;
struct bus_attribute drivers_probe_attr;
int (*match)(struct device * dev, struct device_driver * drv);
int (*uevent)(struct device *dev, char **envp,
int num_envp, char *buffer, int buffer_size);
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 (*suspend_late)(struct device * dev, pm_message_t state);
int (*resume_early)(struct device * dev);
int (*resume)(struct device * dev);
unsigned int drivers_autoprobe:1;
};
其中，当一个总线上的新设备或者新驱动被添加时，*match 函数会被调用。如果指定的驱动程序能够处理指定的设备，该函数返回非零值。
对于spi总线，我们必须调用bus_register(&spi_bus_type)进行注册。调用如果成功，SPI总线子系统将被添加到系统中，在sysfs的/sys/bus目录下可以看到。然后，我们就可以向这个总线添加设备了。代码见下：
static int __init spi_init(void)
{
int status;
buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL);
if (!buf) {
status = -ENOMEM;
goto err0;
}
status = bus_register(&spi_bus_type);
if (status < 0)
goto err1;
status = class_register(&spi_master_class);
if (status < 0)
goto err2;
return 0;
err2:
bus_unregister(&spi_bus_type);
err1:
kfree(buf);
buf = NULL;
err0:
return status;
}
设备
spi设备的结构如下：
#spi.h
struct spi_device {
struct device dev;
struct spi_master *master;
u32 max_speed_hz;
u8 chip_select;
u8 mode;
#define SPI_CPHA 0x01 /* clock phase */
#define SPI_CPOL 0x02 /* clock polarity */
#define SPI_MODE_0 (0|0) /* (original MicroWire) */
#define SPI_MODE_1 (0|SPI_CPHA)
#define SPI_MODE_2 (SPI_CPOL|0)
#define SPI_MODE_3 (SPI_CPOL|SPI_CPHA)
#define SPI_CS_HIGH 0x04 /* chipselect active high? */
#define SPI_LSB_FIRST 0x08 /* per-word bits-on-wire */
#define SPI_3WIRE 0x10 /* SI/SO signals shared */
#define SPI_LOOP 0x20 /* loopback mode */
u8 bits_per_word;
int irq;
void *controller_state;
void *controller_data;
const char *modalias;
/*
* likely need more hooks for more protocol options affecting how
* the controller talks to each chip, like:
* - memory packing (12 bit samples into low bits, others zeroed)
* - priority
* - drop chipselect after each word
* - chipselect delays
* - ...
*/
};
device结构中包含了设备模型核心用来模拟系统的信息。spidev还有设备的其他信息，因此spi设备结构包含在spidev_data结构里。
struct spidev_data {
struct device dev;
struct spi_device *spi;
struct list_head device_entry;
struct mutex buf_lock;
unsigned users;
u8 *buffer;
};
注册spi设备，
#spidev.c
static int spidev_probe(struct spi_device *spi)
{
…
…
status = device_register(&spidev->dev);
…
…
}
完成这个调用之后，我们就可以在sysfs中看到它了。
SPI设备驱动程序
spi驱动程序结构如下：
struct spi_driver {
int (*probe)(struct spi_device *spi);
int (*remove)(struct spi_device *spi);
void (*shutdown)(struct spi_device *spi);
int (*suspend)(struct spi_device *spi, pm_message_t mesg);
int (*resume)(struct spi_device *spi);
struct device_driver driver;
};
spi驱动程序注册函数如下：
int spi_register_driver(struct spi_driver *sdrv)
{
sdrv->driver.bus = &spi_bus_type;
if (sdrv->probe)
sdrv->driver.probe = spi_drv_probe;
if (sdrv->remove)
sdrv->driver.remove = spi_drv_remove;
if (sdrv->shutdown)
sdrv->driver.shutdown = spi_drv_shutdown;
return driver_register(&sdrv->driver);
}
spidev的驱动名如下：
static struct spi_driver spidev_spi = {
.driver = {
.name = "spidev",
.owner = THIS_MODULE,
},
.probe = spidev_probe,
.remove = __devexit_p(spidev_remove),
};
一个spi_register_driver调用将spidev添加到系统中。一旦初始化完成，就可以在sysfs中看到驱动程序信息。
类
spidev类结构如下:
static struct class spidev_class = {
.name = "spidev",
.owner = THIS_MODULE,
.dev_release = spidev_classdev_release,
};
AT91RM9200 SPIDEV初始化
AT91RM9200的spi驱动，对于EK板，原先的SPI是用于dataflash的。其代码如下：
static struct spi_board_info ek_spi_devices[] = {
{ /* DataFlash chip */
.modalias = "mtd_dataflash",
.chip_select = 0,
.max_speed_hz = 15 * 1000 * 1000,
}，
我们需要将.modalias改成我们自己的spi设备名
在spi设备初始化代码中，class_register(&spidev_class)注册类，spi_register_driver(&spidev_spi)注册spidev驱动。
#drivers/spi/spidev.c
static int __init spidev_init(void)
{
int status;
/* Claim our 256 reserved device numbers. Then register a class
* that will key udev/mdev to add/remove /dev nodes. Last, register
* the driver which manages those device numbers.
*/
BUILD_BUG_ON(N_SPI_MINORS > 256);
status = register_chrdev(SPIDEV_MAJOR, "spi", &spidev_fops);
if (status < 0)
return status;
status = class_register(&spidev_class);
if (status < 0) {
unregister_chrdev(SPIDEV_MAJOR, spidev_spi.driver.name);
return status;
}
status = spi_register_driver(&spidev_spi);
if (status < 0) {
class_unregister(&spidev_class);
unregister_chrdev(SPIDEV_MAJOR, spidev_spi.driver.name);
}
return status;
}
挂载/sys
mount –t sysfs sysfs /sys
可以看到有/sys/class/spidev/spidev0.0，表明设备已经挂载在总线上了，同时与驱动联系起来。
使用mdev –s，可以在/dev下看到spidev0.0这个设备了。
自此，spi设备驱动就可以工作了。
测试程序：
|
#include <unistd.h> #include <stdlib.h> #include <fcntl.h> #include <string.h>
#include <sys/ioctl.h> #include <sys/types.h> #include <sys/stat.h>
#include <linux/types.h> #include <linux/spi/spidev.h>
static int verbose;
static void do_read(int fd, int len) { unsigned char buf[32], *bp; int status;
/* read at least 2 bytes, no more than 32 */ if (len < 2) len = 2; else if (len > sizeof(buf)) len = sizeof(buf); memset(buf, 0, sizeof buf);
status = read(fd, buf, len); if (status < 0) { perror("read"); return; } if (status != len) { fprintf(stderr, "short read/n"); return; }
printf("read(%2d, %2d): %02x %02x,", len, status, buf[0], buf[1]); status -= 2; bp = buf + 2; while (status-- > 0) printf(" %02x", *bp++); printf("/n"); }
static void do_msg(int fd, int len) { struct spi_ioc_transfer xfer[2]; unsigned char buf[32], *bp; int status;
memset(xfer, 0, sizeof xfer); memset(buf, 0, sizeof buf);
if (len > sizeof buf) len = sizeof buf;
buf[0] = 0xaa; xfer[0].tx_buf = (__u64) buf; xfer[0].len = 1;
xfer[1].rx_buf = (__u64) buf; xfer[1].len = len;
status = ioctl(fd, SPI_IOC_MESSAGE(2), xfer); if (status < 0) { perror("SPI_IOC_MESSAGE"); return; }
printf("response(%2d, %2d): ", len, status); for (bp = buf; len; len--) printf(" %02x", *bp++); printf("/n"); }
static void dumpstat(const char *name, int fd) { __u8 mode, lsb, bits; __u32 speed;
if (ioctl(fd, SPI_IOC_RD_MODE, &mode) < 0) { perror("SPI rd_mode"); return; } if (ioctl(fd, SPI_IOC_RD_LSB_FIRST, &lsb) < 0) { perror("SPI rd_lsb_fist"); return; } if (ioctl(fd, SPI_IOC_RD_BITS_PER_WORD, &bits) < 0) { perror("SPI bits_per_word"); return; } if (ioctl(fd, SPI_IOC_RD_MAX_SPEED_HZ, &speed) < 0) { perror("SPI max_speed_hz"); return; }
printf("%s: spi mode %d, %d bits %sper word, %d Hz max/n", name, mode, bits, lsb ? "(lsb first) " : "", speed); }
int main(int argc, char **argv) { int c; int readcount = 0; int msglen = 0; int fd; const char *name;
while ((c = getopt(argc, argv, "hm:r:v")) != EOF) { switch (c) { case 'm': msglen = atoi(optarg); if (msglen < 0) goto usage; continue; case 'r': readcount = atoi(optarg); if (readcount < 0) goto usage; continue; case 'v': verbose++; continue; case 'h': case '?': usage: fprintf(stderr, "usage: %s [-h] [-m N] [-r N] /dev/spidevB.D/n", argv[0]); return 1; } }
if ((optind + 1) != argc) goto usage; name = argv[optind];
fd = open(name, O_RDWR); if (fd < 0) { perror("open"); return 1; }
dumpstat(name, fd);
if (msglen) do_msg(fd, msglen);
if (readcount) do_read(fd, readcount);
close(fd); return 0; } |
备注：
如果要设置模式，速率等，则可仿照以下语句：
speed =10*1000*1000; //10MHz
if (ioctl(fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed) < 0) {
perror("SPI max_speed_hz");
return;
}
默认spi_io_transfer时，每个字节之间有延时。在atmel_spi_setup.c文件里去掉该延时语句：
/* TODO: DLYBS and DLYBCT */
//csr |= SPI_BF(DLYBS, 10);
//csr |= SPI_BF(DLYBCT, 10);
这样就可以达到无间隙快速传输批量数据。
标准read(),write()两个函数仅适用于半双工传输，。在传输之间不激活片选。而SPI_IOC_MESSAGE(N)则是全双工传输，并且片选始终激活。
SPI_IOC_MESSAGE传输长度有限制，默认是一页的长度，但是可以更改。
spi_ioc_transfer结构的spi长度 是字节长度，16位传输的时候要注意。