drm/i915/ttm: add i915_sg_from_buddy_resource

We need to be able to build an sg table from our list of buddy blocks,
so that we can later plug this into our ttm backend, and replace our use
of the range manager.
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210616152501.394518-2-matthew.auld@intel.com

drivers/gpu/drm/i915/i915_scatterlist.c

@@ -6,6 +6,9 @@
 
 #include "i915_scatterlist.h"
 
+#include "i915_buddy.h"
+#include "i915_ttm_buddy_manager.h"
+
 #include <drm/drm_mm.h>
 
 #include <linux/slab.h>
@@ -104,6 +107,83 @@ struct sg_table *i915_sg_from_mm_node(const struct drm_mm_node *node,
 	return st;
 }
 
+/**
+ * i915_sg_from_buddy_resource - Create an sg_table from a struct
+ * i915_buddy_block list
+ * @res: The struct i915_ttm_buddy_resource.
+ * @region_start: An offset to add to the dma addresses of the sg list.
+ *
+ * Create a struct sg_table, initializing it from struct i915_buddy_block list,
+ * taking a maximum segment length into account, splitting into segments
+ * if necessary.
+ *
+ * Return: A pointer to a kmalloced struct sg_table on success, negative
+ * error code cast to an error pointer on failure.
+ */
+struct sg_table *i915_sg_from_buddy_resource(struct ttm_resource *res,
+					     u64 region_start)
+{
+	struct i915_ttm_buddy_resource *bman_res = to_ttm_buddy_resource(res);
+	const u64 size = res->num_pages << PAGE_SHIFT;
+	const u64 max_segment = rounddown(UINT_MAX, PAGE_SIZE);
+	struct i915_buddy_mm *mm = bman_res->mm;
+	struct list_head *blocks = &bman_res->blocks;
+	struct i915_buddy_block *block;
+	struct scatterlist *sg;
+	struct sg_table *st;
+	resource_size_t prev_end;
+
+	GEM_BUG_ON(list_empty(blocks));
+
+	st = kmalloc(sizeof(*st), GFP_KERNEL);
+	if (!st)
+		return ERR_PTR(-ENOMEM);
+
+	if (sg_alloc_table(st, res->num_pages, GFP_KERNEL)) {
+		kfree(st);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	sg = st->sgl;
+	st->nents = 0;
+	prev_end = (resource_size_t)-1;
+
+	list_for_each_entry(block, blocks, link) {
+		u64 block_size, offset;
+
+		block_size = min_t(u64, size, i915_buddy_block_size(mm, block));
+		offset = i915_buddy_block_offset(block);
+
+		while (block_size) {
+			u64 len;
+
+			if (offset != prev_end || sg->length >= max_segment) {
+				if (st->nents)
+					sg = __sg_next(sg);
+
+				sg_dma_address(sg) = region_start + offset;
+				sg_dma_len(sg) = 0;
+				sg->length = 0;
+				st->nents++;
+			}
+
+			len = min(block_size, max_segment - sg->length);
+			sg->length += len;
+			sg_dma_len(sg) += len;
+
+			offset += len;
+			block_size -= len;
+
+			prev_end = offset;
+		}
+	}
+
+	sg_mark_end(sg);
+	i915_sg_trim(st);
+
+	return st;
+}
+
 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
 #include "selftests/scatterlist.c"
 #endif

drivers/gpu/drm/i915/i915_scatterlist.h

@@ -14,6 +14,7 @@
 #include "i915_gem.h"
 
 struct drm_mm_node;
+struct ttm_resource;
 
 /*
  * Optimised SGL iterator for GEM objects
@@ -145,4 +146,8 @@ bool i915_sg_trim(struct sg_table *orig_st);
 
 struct sg_table *i915_sg_from_mm_node(const struct drm_mm_node *node,
 				      u64 region_start);
+
+struct sg_table *i915_sg_from_buddy_resource(struct ttm_resource *res,
+					     u64 region_start);
+
 #endif