// SPDX-License-Identifier: GPL-2.0
  /*
   *	lib/dma-noop.c
   *
   * DMA operations that map to physical addresses without flushing memory.
   */
  #include <linux/export.h>
  #include <linux/mm.h>
  #include <linux/dma-mapping.h>
  #include <linux/scatterlist.h>
  #include <linux/pfn.h>
  
  static void *dma_noop_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 = virt_to_phys(ret) - PFN_PHYS(dev->dma_pfn_offset);
  
  	return ret;
  }
  
  static void dma_noop_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_noop_map_page(struct device *dev, struct page *page,
  				      unsigned long offset, size_t size,
  				      enum dma_data_direction dir,
  				      unsigned long attrs)
  {
  	return page_to_phys(page) + offset - PFN_PHYS(dev->dma_pfn_offset);
  }
  
  static int dma_noop_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) {
  		dma_addr_t offset = PFN_PHYS(dev->dma_pfn_offset);
  		void *va;
  
  		BUG_ON(!sg_page(sg));
  		va = sg_virt(sg);
  		sg_dma_address(sg) = (dma_addr_t)virt_to_phys(va) - offset;
  		sg_dma_len(sg) = sg->length;
  	}
  
  	return nents;
  }
  
  const struct dma_map_ops dma_noop_ops = {
  	.alloc			= dma_noop_alloc,
  	.free			= dma_noop_free,
  	.map_page		= dma_noop_map_page,
  	.map_sg			= dma_noop_map_sg,
  };
  
  EXPORT_SYMBOL(dma_noop_ops);