求指点！修改使用spidev源码时发现spi_read/spi_write接口没用？！
本帖最后由 acrazyworld 于 2012-03-28 15:19 编辑在下使用的是tq2440开发板，linux2.6.30。正在使用spi0驱动一个RF模块，本人没有用iomap的方法直接配置spi寄存器，而是想利用linux自己的spi驱动体系来编写设备驱动。
（1）已经在加上了spi0总线，在/sys/device/platform/下有了s3c2410-spi0目录。
（2）将spidev.h,spidev.c抠出来加以修改，编译.ko驱动模块，insmod模块。然后连接MISO-MOSI，在测试的应用程序中使用 ioctl (fd, SPI_IOC_MESSAGE (1), &tr)进行IO同步的方法可以读写数据。应用层的测试代码：
static void
transfer (int fd)
{
int ret;
uint8_t tx[] = {
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0x40, 0x00, 0x00, 0x00, 0x00, 0x95,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xDE, 0xAD, 0xBE, 0xEF, 0xBA, 0xAD,
0xF0, 0x0D,
};
uint8_t rx = { 0, };
struct spi_ioc_transfer tr = {
.tx_buf = (unsigned long) tx,
.rx_buf = (unsigned long) rx,
.len = ARRAY_SIZE (tx),
.delay_usecs = delay,
.speed_hz = speed,
.bits_per_word = bits,
};
ret = ioctl (fd, SPI_IOC_MESSAGE (1), &tr);
if (ret == 1)
pabort ("can't send spi message");
for (ret = 0; ret < ARRAY_SIZE (tx); ret++)
{
if (!(ret % 6))
puts ("");
printf ("%.2X ", rx);
}
puts ("");
}
（3）问题来了！为了在内核使用spi_read,spi_write等接口，我在spidev_probe中加入其测试代码后发现spi_read,spi_write根本没有读写成功！spidev.c添加的测试代码如下：
static int spidev_probe(struct spi_device *spi)
{
。。。省略。。。
/*test code*/
printk("test 3 start!\n");
if(spi_write(spidev->spi,tx_buf,8)< 0){
printk("spi_write write error!\n");
}
if(spi_read (spidev->spi,rx_buf,8)){
printk("spi_write read error!\n");
}
for(i = 0; i < 8; i++){
printk("{%2x}\n",rx_buf);
}
printk("test 4 start!\n");
for(i = 0; i < 8; i++){
printk("{%2x}\n",spi_w8r8(spidev->spi,i));
}
printk("test end!\n");
。。。省略。。。
return status;
}
小弟就不明白了，由于（2）测试成功，说明spi总线加上了，硬件层的配置也没问题了，而使用probe中传入的spi_device设备在内核进行spi_read,spi_write操作却没有成功？难道是那个地方没有设置的原因？ 引用文档spidev
Normal open() and close() operations on /dev/spidevB.D files work as you
would expect.
Standard read() and write() operations are obviously only half-duplex, and
the chipselect is deactivated between those operations.Full-duplex access,
and composite operation without chipselect de-activation, is available using
the SPI_IOC_MESSAGE(N) request.
传统的read write使用的是半双工模式，需要cs片选；而 SPI_IOC_MESSAGE(N) 方式使用全双工，无须片选。
Several ioctl() requests let your driver read or override the device's current
settings for data transfer parameters:
SPI_IOC_RD_MODE, SPI_IOC_WR_MODE ... pass a pointer to a byte which will
return (RD) or assign (WR) the SPI transfer mode.Use the constants
SPI_MODE_0..SPI_MODE_3; or if you prefer you can combine SPI_CPOL
(clock polarity, idle high iff this is set) or SPI_CPHA (clock phase,
sample on trailing edge iff this is set) flags.
SPI_IOC_RD_LSB_FIRST, SPI_IOC_WR_LSB_FIRST ... pass a pointer to a byte
which will return (RD) or assign (WR) the bit justification used to
transfer SPI words.Zero indicates MSB-first; other values indicate
the less common LSB-first encoding.In both cases the specified value
is right-justified in each word, so that unused (TX) or undefined (RX)
bits are in the MSBs.
SPI_IOC_RD_BITS_PER_WORD, SPI_IOC_WR_BITS_PER_WORD ... pass a pointer to
a byte which will return (RD) or assign (WR) the number of bits in
each SPI transfer word.The value zero signifies eight bits.
SPI_IOC_RD_MAX_SPEED_HZ, SPI_IOC_WR_MAX_SPEED_HZ ... pass a pointer to a
u32 which will return (RD) or assign (WR) the maximum SPI transfer
speed, in Hz.The controller can't necessarily assign that specific
clock speed.
NOTES:
- At this time there is no async I/O support; everything is purely
synchronous.都是同步的？
- There's currently no way to report the actual bit rate used to
shift data to/from a given device.
- From userspace, you can't currently change the chip select polarity;
that could corrupt transfers to other devices sharing the SPI bus.
Each SPI device is deselected when it's not in active use, allowing
other drivers to talk to other devices.
- There's a limit on the number of bytes each I/O request can transfer
to the SPI device.It defaults to one page, but that can be changed
using a module parameter.
- Because SPI has no low-level transfer acknowledgement, you usually
won't see any I/O errors when talking to a non-existent device.
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