linux3.10.65 DMA缓冲区分配失败

来源：互联网发布：微信网络错误编辑：程序博客网时间：2024/06/11 12:54

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;elsereturn 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NULLreturn 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;}

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