i2c-dev模組--read/write支援DMA傳輸_kernel-i2c子系統

開啟核心配置項CONFIG_I2C_CHARDEV，載入i2c-dev模組。

裝置節點：/dev/i2c-x。

使用者空間通過裝置節點訪問掛載到i2c適配器上的任意i2c裝置。.

i2c-dev模組的read/write函數不支援block傳輸，一次最多傳輸8位元組資料。

修改read/write函數支援DMA傳輸，以實現block傳輸。DMA傳輸 BUFFER 大小的限制是255位元組。

代碼修改如下：i2c-dev.c

#include<linux/dma-mapping.h>

#define MAX_BUFFER_SIZE 255

static ssize_t i2cdev_write_dma(struct file *file,const char __user *buf, size_t count, loff_t *offset)

{

int ret;

struct i2c_client *client = file->private_data;

char *pI2cDMAWriteBuf = NULL;

unsigned int PhyAddrForDMABuf = 0;

if (count > MAX_BUFFER_SIZE )

count  = MAX_BUFFER_SIZE ;

pI2cDMAWriteBuf  = (char *)dma_alloc_coherent(NULL,  MAX_BUFFER_SIZE ,&PhyAddrForDMABuf , GFP_KERNEL);

if (pI2cDMAWriteBuf   == NULL)

{

return -ENOMEM;

}

if (copyt_from_user(pI2cDMAWriteBuf  , buf, count))

{

// error

dma_free_coherent(NULL, MAX_BUFFER_SIZE ,  pI2cDMAWriteBuf  , PhyAddrForDMABuf );

pI2cDMAWriteBuf  = NULL;

PhyAddrForDMABuf  = 0;

return -EFAULT;

}

client->addr &= I2C_MASK_FLAG;

client->ext_flag |= I2C_DMA_FLAG;

client->ext_flag |= I2C_A_FILTER_MSG;

ret = i2c_master_sent(client, (unsigned char *)PhyAddrForDMABuf, count);

dma_free_coherent(NULL, MAX_BUFFER_SIZE ,  pI2cDMAWriteBuf  , PhyAddrForDMABuf );

pI2cDMAWriteBuf  = NULL;

PhyAddrForDMABuf  = 0;

return ret;

}

static ssize_t i2cdev_write_dma(struct file *file,const char __user *buf, size_t count, loff_t *offset)

{

int ret;

struct i2c_client *client = file->private_data;

char *pI2cDMAReadBuf = NULL;

unsigned int PhyAddrForDMABuf = 0;

if (count > MAX_BUFFER_SIZE )

count  = MAX_BUFFER_SIZE ;

pI2cDMAReadBuf = (char *)dma_alloc_coherent(NULL,  MAX_BUFFER_SIZE , &PhyAddrForDMABuf, GFP_KERNEL);

if (pI2cDMAReadBuf == NULL)

{

return -ENOMEM;

}

client->addr &= I2C_MASK_FLAG;

client->ext_flag |= I2C_DMA_FLAG;

client->ext_flag |= I2C_A_FILTER_MSG;

ret = i2c_master_recv(client, (unsigned char *)PhyAddrForDMABuf, count);
if (ret >= 0)
{
if(copy_to_user(buf, pI2cDMAReadBuf, ret))
{
   ret = -EFAULT;
}
}

dma_free_coherent(NULL, MAX_BUFFER_SIZE ,  pI2cDMAReadBuf, PhyAddrForDMABuf );

pI2cDMAWriteBuf  = NULL;

PhyAddrForDMABuf  = 0;

return ret;

}

static const struct file_operations i2cdev_fops = {
...
.read= i2cdev_read_dma,
.write = i2cdev_write_dma,
};