问让用户读写物理地址的dma_common_mmap文档

EN

/**
 * dma_mmap_attrs - map a coherent DMA allocation into user space
 * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
 * @vma: vm_area_struct describing requested user mapping
 * @cpu_addr: kernel CPU-view address returned from dma_alloc_attrs
 * @handle: device-view address returned from dma_alloc_attrs
 * @size: size of memory originally requested in dma_alloc_attrs
 * @attrs: attributes of mapping properties requested in dma_alloc_attrs
 *
 * Map a coherent DMA buffer previously allocated by dma_alloc_attrs
 * into user space.  The coherent DMA buffer must not be freed by the
 * driver until the user space mapping has been released.
 */
static inline int
dma_mmap_attrs(struct device *dev, struct vm_area_struct *vma, void *cpu_addr,
           dma_addr_t dma_addr, size_t size, struct dma_attrs *attrs)
{
    struct dma_map_ops *ops = get_dma_ops(dev);
    BUG_ON(!ops);
    if (ops->mmap)
        return ops->mmap(dev, vma, cpu_addr, dma_addr, size, attrs);
    return dma_common_mmap(dev, vma, cpu_addr, dma_addr, size);
}

#define dma_mmap_coherent(d, v, c, h, s) dma_mmap_attrs(d, v, c, h, s, NULL)