[PATCH 04/15] drm/i915: use the max sg->length if the dma_map fails

[Matthew Auld]

If the dma_map fails it would make more sense to consider the max
sg->length rather than the max_segment when deciding if it's worthwhile
rebuilding the sg table with a smaller max_segment.

Signed-off-by: Matthew Auld <matthew.auld at intel.com>
---
 drivers/gpu/drm/i915/i915_gem.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index e16fc8ec3361..65fbb823ab0a 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2337,6 +2337,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 	struct page *page;
 	unsigned long last_pfn = 0;	/* suppress gcc warning */
 	unsigned int max_segment;
+	unsigned int max_sg_length;
 	int ret;
 	gfp_t gfp;
 
@@ -2351,6 +2352,8 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 	if (!max_segment)
 		max_segment = rounddown(UINT_MAX, PAGE_SIZE);
 
+	max_sg_length = PAGE_SIZE;
+
 	st = kmalloc(sizeof(*st), GFP_KERNEL);
 	if (st == NULL)
 		return ERR_PTR(-ENOMEM);
@@ -2404,8 +2407,10 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 		if (!i ||
 		    sg->length >= max_segment ||
 		    page_to_pfn(page) != last_pfn + 1) {
-			if (i)
+			if (i) {
+				max_sg_length = max(max_sg_length, sg->length);
 				sg = sg_next(sg);
+			}
 			st->nents++;
 			sg_set_page(sg, page, PAGE_SIZE, 0);
 		} else {
@@ -2428,7 +2433,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 		 * it could not reserve enough large entries, asking
 		 * for PAGE_SIZE chunks instead may be helpful.
 		 */
-		if (max_segment > PAGE_SIZE) {
+		if (max_sg_length > PAGE_SIZE) {
 			for_each_sgt_page(page, sgt_iter, st)
 				put_page(page);
 			sg_free_table(st);
-- 
2.9.3