linux中分配dma缓冲区,linux3.10.65 DMA缓冲区分配失败

今天调试tp固件升级的时候，DMA缓冲区按照以前android4.2(内核版本不记得了),DMA缓冲区的申请方式，发现老是申请失败。原来的申请方式如下：

static u8 *I2CDMABuf_va = NULL;

dma_addr_t I2CDMABuf_pa =NULL;

I2CDMABuf_va = (u8 *)dma_alloc_coherent(NULL, FTS_DMA_BUF_SIZE, (dma_addr_t *)&I2CDMABuf_pa, GFP_KERNEL);

if(!I2CDMABuf_va)

{

dev_dbg(&client->dev,"%s Allocate DMA I2C Buffer failed!\n",__func__);

snprintf(dma_alloc_buf, 100,

"Allocate DMA I2C Buffer failed!\n");

return -EIO;

}分析dma_alloc_coherent源码发现如下：

static inline void *dma_alloc_coherent(struct device *dev, size_t size,

dma_addr_t *dma_handle, gfp_t flags)

{

struct dma_map_ops *ops = get_dma_ops(dev);//得到dma映射操作集

void *vaddr;

if (dma_alloc_from_coherent(dev, size, dma_handle, &vaddr))

return vaddr;

vaddr = ops->alloc(dev, size, dma_handle, flags, NULL);

debug_dma_alloc_coherent(dev, size, *dma_handle, vaddr);

return vaddr;

}get_dma_ops源码如下：

static inline struct dma_map_ops *get_dma_ops(struct device *dev)

{

if (unlikely(!dev) || !dev->archdata.dma_ops)//dev为NULL，

return dma_ops;

else

return dev->archdata.dma_ops;

}因为传递进来的参数dev为NULL，所以这里返回dma_ops。再来看dma_alloc_from_coherent这个方法，一致性DMA映射：

int dma_alloc_from_coherent(struct device *dev, ssize_t size,

dma_addr_t *dma_handle, void **ret)

{

struct dma_coherent_mem *mem;

int order = get_order(size);

int pageno;

if (!dev)//dev为NULL

return 0;

mem = dev->dma_mem;

if (!mem)

return 0;

*ret = NULL;

if (unlikely(size > (mem->size << PAGE_SHIFT)))

goto err;

pageno = bitmap_find_free_region(mem->bitmap, mem->size, order);

if (unlikely(pageno < 0))

goto err;

/*

* Memory was found in the per-device area.

*/

*dma_handle = mem->device_base + (pageno << PAGE_SHIFT);

*ret = mem->virt_base + (pageno << PAGE_SHIFT);

memset(*ret, 0, size);

return 1;

err:

/*

* In the case where the allocation can not be satisfied from the

* per-device area, try to fall back to generic memory if the

* constraints allow it.

*/

return mem->flags & DMA_MEMORY_EXCLUSIVE;

}因为dev为NULL，所以这里返回0。所以直接返回了一个未初始化的vaddr的指针。所以，新的内核版本中dma_alloc_coherent的第一个device参数不能为NULL，否则，DMA缓冲区会分配失败。如下：

I2CDMABuf_va = (u8 *)dma_alloc_coherent(&client->dev, FTS_DMA_BUF_SIZE, (dma_addr_t *)&I2CDMABuf_pa, GFP_KERNEL);

if(!I2CDMABuf_va)

{

dev_dbg(&client->dev,"%s Allocate DMA I2C Buffer failed!\n",__func__);

snprintf(dma_alloc_buf, 100,

"Allocate DMA I2C Buffer failed!\n");

return -EIO;

}