// SPDX-License-Identifier: GPL-2.0
  /*
   *	lib/dma-virt.c
   *
   * DMA operations that map to virtual addresses without flushing memory.
   */
  #include <linux/export.h>
  #include <linux/mm.h>
  #include <linux/dma-mapping.h>
  #include <linux/scatterlist.h>
  
  static void *dma_virt_alloc(struct device *dev, size_t size,
  			    dma_addr_t *dma_handle, gfp_t gfp,
  			    unsigned long attrs)
  {
  	void *ret;
  
  	ret = (void *)__get_free_pages(gfp, get_order(size));
  	if (ret)
  		*dma_handle = (uintptr_t)ret;
  	return ret;
  }
  
  static void dma_virt_free(struct device *dev, size_t size,
  			  void *cpu_addr, dma_addr_t dma_addr,
  			  unsigned long attrs)
  {
  	free_pages((unsigned long)cpu_addr, get_order(size));
  }
  
  static dma_addr_t dma_virt_map_page(struct device *dev, struct page *page,
  				    unsigned long offset, size_t size,
  				    enum dma_data_direction dir,
  				    unsigned long attrs)
  {
  	return (uintptr_t)(page_address(page) + offset);
  }
  
  static int dma_virt_map_sg(struct device *dev, struct scatterlist *sgl,
  			   int nents, enum dma_data_direction dir,
  			   unsigned long attrs)
  {
  	int i;
  	struct scatterlist *sg;
  
  	for_each_sg(sgl, sg, nents, i) {
  		BUG_ON(!sg_page(sg));
  		sg_dma_address(sg) = (uintptr_t)sg_virt(sg);
  		sg_dma_len(sg) = sg->length;
  	}
  
  	return nents;
  }
  
  const struct dma_map_ops dma_virt_ops = {
  	.alloc			= dma_virt_alloc,
  	.free			= dma_virt_free,
  	.map_page		= dma_virt_map_page,
  	.map_sg			= dma_virt_map_sg,
  };
  EXPORT_SYMBOL(dma_virt_ops);