[PATCH 18/23] drm/i915: add i915_sg_from_buddy_blocks

[Matthew Auld]

We do this is two parts: first allocate the blocks and the build an sg
from said blocks, which can then easily hook into our existing
get_pages() stuff.

Signed-off-by: Matthew Auld <matthew.auld at intel.com>
---
 drivers/gpu/drm/i915/i915_scatterlist.c | 77 +++++++++++++++++++++++++
 drivers/gpu/drm/i915/i915_scatterlist.h |  5 ++
 2 files changed, 82 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_scatterlist.c b/drivers/gpu/drm/i915/i915_scatterlist.c
index 69e9e6c3135e..2fd61e0391de 100644
--- a/drivers/gpu/drm/i915/i915_scatterlist.c
+++ b/drivers/gpu/drm/i915/i915_scatterlist.c
@@ -6,9 +6,12 @@
 
 #include "i915_scatterlist.h"
 
+#include "i915_buddy.h"
+
 #include <drm/drm_mm.h>
 
 #include <linux/slab.h>
+#include <linux/io-mapping.h>
 
 bool i915_sg_trim(struct sg_table *orig_st)
 {
@@ -104,6 +107,80 @@ struct sg_table *i915_sg_from_mm_node(const struct drm_mm_node *node,
 	return st;
 }
 
+/**
+ * i915_sg_from_buddy_blocks - Create an sg_table from a struct i915_buddy_block list
+ * @node: The list of i915_buddy_block.
+ * @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_blocks(struct list_head *blocks,
+					   u64 size,
+					   u64 region_start)
+{
+	const u64 max_segment = UINT_MAX;
+	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, size >> PAGE_SHIFT, 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) {
+		struct i915_buddy_mm *mm = block->private;
+		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
diff --git a/drivers/gpu/drm/i915/i915_scatterlist.h b/drivers/gpu/drm/i915/i915_scatterlist.h
index 5acca45ea981..25f9803ddd5e 100644
--- a/drivers/gpu/drm/i915/i915_scatterlist.h
+++ b/drivers/gpu/drm/i915/i915_scatterlist.h
@@ -145,4 +145,9 @@ 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_blocks(struct list_head *blocks,
+					   u64 size,
+					   u64 region_start);
+
 #endif
-- 
2.26.3