staging: comedi: comedidev.h: document struct comedi_buf_map

	unsigned int *readback;

};

/**

 * struct comedi_buf_page - Describe a page of a COMEDI buffer

 * @virt_addr: Kernel address of page.

 * @dma_addr: DMA address of page if in DMA coherent memory.

 */

struct comedi_buf_page {

	void *virt_addr;

	dma_addr_t dma_addr;

};

/**

 * struct comedi_buf_map - Describe pages in a COMEDI buffer

 * @dma_hw_dev: Low-level hardware &struct device pointer copied from the

 *	COMEDI device's hw_dev member.

 * @page_list: Pointer to array of &struct comedi_buf_page, one for each

 *	page in the buffer.

 * @n_pages: Number of pages in the buffer.

 * @dma_dir: DMA direction used to allocate pages of DMA coherent memory,

 *	or %DMA_NONE if pages allocated from regular memory.

 * @refcount: &struct kref reference counter used to free the buffer.

 *

 * A COMEDI data buffer is allocated as individual pages, either in

 * conventional memory or DMA coherent memory, depending on the attached,

 * low-level hardware device.  (The buffer pages also get mapped into the

 * kernel's contiguous virtual address space pointed to by the 'prealloc_buf'

 * member of &struct comedi_async.)

 *

 * The buffer is normally freed when the COMEDI device is detached from the

 * low-level driver (which may happen due to device removal), but if it happens

 * to be mmapped at the time, the pages cannot be freed until the buffer has

 * been munmapped.  That is what the reference counter is for.  (The virtual

 * address space pointed by 'prealloc_buf' is freed when the COMEDI device is

 * detached.)

 */

struct comedi_buf_map {

	struct device *dma_hw_dev;

	struct comedi_buf_page *page_list;