text: /*
   * SPDX-License-Identifier: MIT
   *
   * Copyright © 2016 Intel Corporation
   */
  
  #ifndef I915_SCATTERLIST_H
  #define I915_SCATTERLIST_H
  
  #include <linux/pfn.h>
  #include <linux/scatterlist.h>
  #include <linux/swiotlb.h>
  
  #include "i915_gem.h"
  
  /*
   * Optimised SGL iterator for GEM objects
   */
  static __always_inline struct sgt_iter {
  	struct scatterlist *sgp;
  	union {
  		unsigned long pfn;
  		dma_addr_t dma;
  	};
  	unsigned int curr;
  	unsigned int max;
  } __sgt_iter(struct scatterlist *sgl, bool dma) {
  	struct sgt_iter s = { .sgp = sgl };
  
  	if (s.sgp) {
  		s.max = s.curr = s.sgp->offset;
  		s.max += s.sgp->length;
  		if (dma)
  			s.dma = sg_dma_address(s.sgp);
  		else
  			s.pfn = page_to_pfn(sg_page(s.sgp));
  	}
  
  	return s;
  }
  
  static inline int __sg_page_count(const struct scatterlist *sg)
  {
  	return sg->length >> PAGE_SHIFT;
  }
  
  static inline struct scatterlist *____sg_next(struct scatterlist *sg)
  {
  	++sg;
  	if (unlikely(sg_is_chain(sg)))
  		sg = sg_chain_ptr(sg);
  	return sg;
  }
  
  /**
   * __sg_next - return the next scatterlist entry in a list
   * @sg:		The current sg entry
   *
   * Description:
   *   If the entry is the last, return NULL; otherwise, step to the next
   *   element in the array (@sg@+1). If that's a chain pointer, follow it;
   *   otherwise just return the pointer to the current element.
   **/
  static inline struct scatterlist *__sg_next(struct scatterlist *sg)
  {
  	return sg_is_last(sg) ? NULL : ____sg_next(sg);
  }
  
  /**
   * __for_each_sgt_daddr - iterate over the device addresses of the given sg_table
   * @__dp:	Device address (output)
   * @__iter:	'struct sgt_iter' (iterator state, internal)
   * @__sgt:	sg_table to iterate over (input)
   * @__step:	step size
   */
  #define __for_each_sgt_daddr(__dp, __iter, __sgt, __step)		\
  	for ((__iter) = __sgt_iter((__sgt)->sgl, true);			\
  	     ((__dp) = (__iter).dma + (__iter).curr), (__iter).sgp;	\
  	     (((__iter).curr += (__step)) >= (__iter).max) ?		\
  	     (__iter) = __sgt_iter(__sg_next((__iter).sgp), true), 0 : 0)
  
  /**
   * for_each_sgt_page - iterate over the pages of the given sg_table
   * @__pp:	page pointer (output)
   * @__iter:	'struct sgt_iter' (iterator state, internal)
   * @__sgt:	sg_table to iterate over (input)
   */
  #define for_each_sgt_page(__pp, __iter, __sgt)				\
  	for ((__iter) = __sgt_iter((__sgt)->sgl, false);		\
  	     ((__pp) = (__iter).pfn == 0 ? NULL :			\
  	      pfn_to_page((__iter).pfn + ((__iter).curr >> PAGE_SHIFT))); \
  	     (((__iter).curr += PAGE_SIZE) >= (__iter).max) ?		\
  	     (__iter) = __sgt_iter(__sg_next((__iter).sgp), false), 0 : 0)
  
  static inline unsigned int i915_sg_page_sizes(struct scatterlist *sg)
  {
  	unsigned int page_sizes;
  
  	page_sizes = 0;
  	while (sg) {
  		GEM_BUG_ON(sg->offset);
  		GEM_BUG_ON(!IS_ALIGNED(sg->length, PAGE_SIZE));
  		page_sizes |= sg->length;
  		sg = __sg_next(sg);
  	}
  
  	return page_sizes;
  }
  
  static inline unsigned int i915_sg_segment_size(void)
  {
  	unsigned int size = swiotlb_max_segment();
  
  	if (size == 0)
  		return SCATTERLIST_MAX_SEGMENT;
  
  	size = rounddown(size, PAGE_SIZE);
  	/* swiotlb_max_segment_size can return 1 byte when it means one page. */
  	if (size < PAGE_SIZE)
  		size = PAGE_SIZE;
  
  	return size;
  }
  
  bool i915_sg_trim(struct sg_table *orig_st);
  
  #endif
  