我们直到dma_alloc_coherent->dma_alloc_attrs
static inline void *dma_alloc_attrs(struct device *dev, size_t size,
dma_addr_t *dma_handle, gfp_t flag,
unsigned long attrs)
{
struct dma_map_ops *ops = get_dma_ops(dev);
void *cpu_addr;
BUG_ON(!ops);
if (dma_alloc_from_coherent(dev, size, dma_handle, &cpu_addr))
return cpu_addr;
if (!arch_dma_alloc_attrs(&dev, &flag))
return NULL;
if (!ops->alloc)
return NULL;
cpu_addr = ops->alloc(dev, size, dma_handle, flag, attrs);
debug_dma_alloc_coherent(dev, size, *dma_handle, cpu_addr);
return cpu_addr;
}
而在dma_alloc_attrs 中会首先调用dma_alloc_from_coherent 会尝试从device自身的memory中分配memory。
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);
unsigned long flags;
int pageno;
int dma_memory_map;
if (!dev)
return 0;
mem = dev->dma_mem;
if (!mem)
return 0;
*ret = NULL;
spin_lock_irqsave(&mem->spinlock, flags);
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);
dma_memory_map = (mem->flags & DMA_MEMORY_MAP);
spin_unlock_irqrestore(&mem->spinlock, flags);
if (dma_memory_map)
memset(*ret, 0, size);
else
memset_io(*ret, 0, size);
return 1;
err:
spin_unlock_irqrestore(&mem->spinlock, flags);
/*
* 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;
}
dma_alloc_from_coherent的实现首先从
mem = dev->dma_mem;中拿到memory信息再从这个mem中分配,可是遍历kernel中所有调用dma_alloc_coherent 的device自身都没有memory,从打印的log看一般都是在dma_alloc_from_coherent 函数中由于mem为null 返回了,还真没有见过自带memory的device.
static inline void *dma_alloc_attrs(struct device *dev, size_t size,
dma_addr_t *dma_handle, gfp_t flag,
unsigned long attrs)
{
struct dma_map_ops *ops = get_dma_ops(dev);
void *cpu_addr;
BUG_ON(!ops);
if (dma_alloc_from_coherent(dev, size, dma_handle, &cpu_addr))
return cpu_addr;
if (!arch_dma_alloc_attrs(&dev, &flag))
return NULL;
if (!ops->alloc)
return NULL;
cpu_addr = ops->alloc(dev, size, dma_handle, flag, attrs);
debug_dma_alloc_coherent(dev, size, *dma_handle, cpu_addr);
return cpu_addr;
}
而在dma_alloc_attrs 中会首先调用dma_alloc_from_coherent 会尝试从device自身的memory中分配memory。
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);
unsigned long flags;
int pageno;
int dma_memory_map;
if (!dev)
return 0;
mem = dev->dma_mem;
if (!mem)
return 0;
*ret = NULL;
spin_lock_irqsave(&mem->spinlock, flags);
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);
dma_memory_map = (mem->flags & DMA_MEMORY_MAP);
spin_unlock_irqrestore(&mem->spinlock, flags);
if (dma_memory_map)
memset(*ret, 0, size);
else
memset_io(*ret, 0, size);
return 1;
err:
spin_unlock_irqrestore(&mem->spinlock, flags);
/*
* 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;
}
dma_alloc_from_coherent的实现首先从
mem = dev->dma_mem;中拿到memory信息再从这个mem中分配,可是遍历kernel中所有调用dma_alloc_coherent 的device自身都没有memory,从打印的log看一般都是在dma_alloc_from_coherent 函数中由于mem为null 返回了,还真没有见过自带memory的device.
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dma_alloc_from_coherent 由于mem为null 返回
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