drm/i915/fb: Factor out functions to remap contiguous FB obj pages

Factor out functions needed to map contiguous FB obj pages to a GTT/DPT
VMA view in the next patch.

While at it s/4096/I915_GTT_PAGE_SIZE/ in add_padding_pages().

No functional changes.

v2: s/4096/I915_GTT_PAGE_SIZE/ (Matthew)
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211026225105.2783797-4-imre.deak@intel.com

drivers/gpu/drm/i915/gt/intel_ggtt.c

@@ -1388,18 +1388,9 @@ intel_rotate_pages(struct intel_rotation_info *rot_info,
 }
 
 static struct scatterlist *
-remap_pages(struct drm_i915_gem_object *obj,
-	    unsigned int offset, unsigned int alignment_pad,
-	    unsigned int width, unsigned int height,
-	    unsigned int src_stride, unsigned int dst_stride,
+add_padding_pages(unsigned int count,
 		  struct sg_table *st, struct scatterlist *sg)
 {
-	unsigned int row;
-
-	if (!width || !height)
-		return sg;
-
-	if (alignment_pad) {
 	st->nents++;
 
 	/*
@@ -1407,11 +1398,28 @@ remap_pages(struct drm_i915_gem_object *obj,
 	 * here is just a convenience to indicate how many padding PTEs
 	 * to insert at this spot.
 	 */
-		sg_set_page(sg, NULL, alignment_pad * 4096, 0);
+	sg_set_page(sg, NULL, count * I915_GTT_PAGE_SIZE, 0);
 	sg_dma_address(sg) = 0;
-		sg_dma_len(sg) = alignment_pad * 4096;
+	sg_dma_len(sg) = count * I915_GTT_PAGE_SIZE;
 	sg = sg_next(sg);
-	}
+
+	return sg;
+}
+
+static struct scatterlist *
+remap_pages(struct drm_i915_gem_object *obj,
+	    unsigned int offset, unsigned int alignment_pad,
+	    unsigned int width, unsigned int height,
+	    unsigned int src_stride, unsigned int dst_stride,
+	    struct sg_table *st, struct scatterlist *sg)
+{
+	unsigned int row;
+
+	if (!width || !height)
+		return sg;
+
+	if (alignment_pad)
+		sg = add_padding_pages(alignment_pad, st, sg);
 
 	for (row = 0; row < height; row++) {
 		unsigned int left = width * I915_GTT_PAGE_SIZE;
@@ -1448,22 +1456,45 @@ remap_pages(struct drm_i915_gem_object *obj,
 		if (!left)
 			continue;
 
-		st->nents++;
-
-		/*
-		 * The DE ignores the PTEs for the padding tiles, the sg entry
-		 * here is just a conenience to indicate how many padding PTEs
-		 * to insert at this spot.
-		 */
-		sg_set_page(sg, NULL, left, 0);
-		sg_dma_address(sg) = 0;
-		sg_dma_len(sg) = left;
-		sg = sg_next(sg);
+		sg = add_padding_pages(left >> PAGE_SHIFT, st, sg);
 	}
 
 	return sg;
 }
 
+static struct scatterlist *
+remap_contiguous_pages(struct drm_i915_gem_object *obj,
+		       unsigned int obj_offset,
+		       unsigned int count,
+		       struct sg_table *st, struct scatterlist *sg)
+{
+	struct scatterlist *iter;
+	unsigned int offset;
+
+	iter = i915_gem_object_get_sg_dma(obj, obj_offset, &offset);
+	GEM_BUG_ON(!iter);
+
+	do {
+		unsigned int len;
+
+		len = min(sg_dma_len(iter) - (offset << PAGE_SHIFT),
+			  count << PAGE_SHIFT);
+		sg_set_page(sg, NULL, len, 0);
+		sg_dma_address(sg) =
+			sg_dma_address(iter) + (offset << PAGE_SHIFT);
+		sg_dma_len(sg) = len;
+
+		st->nents++;
+		count -= len >> PAGE_SHIFT;
+		if (count == 0)
+			return sg;
+
+		sg = __sg_next(sg);
+		iter = __sg_next(iter);
+		offset = 0;
+	} while (1);
+}
+
 static noinline struct sg_table *
 intel_remap_pages(struct intel_remapped_info *rem_info,
 		  struct drm_i915_gem_object *obj)
@@ -1524,9 +1555,8 @@ intel_partial_pages(const struct i915_ggtt_view *view,
 		    struct drm_i915_gem_object *obj)
 {
 	struct sg_table *st;
-	struct scatterlist *sg, *iter;
+	struct scatterlist *sg;
 	unsigned int count = view->partial.size;
-	unsigned int offset;
 	int ret = -ENOMEM;
 
 	st = kmalloc(sizeof(*st), GFP_KERNEL);
@@ -1537,34 +1567,14 @@ intel_partial_pages(const struct i915_ggtt_view *view,
 	if (ret)
 		goto err_sg_alloc;
 
-	iter = i915_gem_object_get_sg_dma(obj, view->partial.offset, &offset);
-	GEM_BUG_ON(!iter);
-
-	sg = st->sgl;
 	st->nents = 0;
-	do {
-		unsigned int len;
 
-		len = min(sg_dma_len(iter) - (offset << PAGE_SHIFT),
-			  count << PAGE_SHIFT);
-		sg_set_page(sg, NULL, len, 0);
-		sg_dma_address(sg) =
-			sg_dma_address(iter) + (offset << PAGE_SHIFT);
-		sg_dma_len(sg) = len;
+	sg = remap_contiguous_pages(obj, view->partial.offset, count, st, st->sgl);
 
-		st->nents++;
-		count -= len >> PAGE_SHIFT;
-		if (count == 0) {
 	sg_mark_end(sg);
 	i915_sg_trim(st); /* Drop any unused tail entries. */
 
 	return st;
-		}
-
-		sg = __sg_next(sg);
-		iter = __sg_next(iter);
-		offset = 0;
-	} while (1);
 
 err_sg_alloc:
 	kfree(st);