[Intel-gfx] [PATCH v2] drm/i915: Allow compaction upto SWIOTLB max segment size

[Chris Wilson]

commit 1625e7e549c5 ("drm/i915: make compact dma scatter lists creation
work with SWIOTLB backend") took a heavy handed approach to undo the
scatterlist compaction in the face of SWIOTLB. (The compaction hit a bug
whereby we tried to pass a segment larger than SWIOTLB could handle.) We
can be a little more intelligent and try compacting the scatterlist up
to the maximum SWIOTLB segment size (when using SWIOTLB).

v2: Tidy sg_mark_end() and cpp

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
CC: Imre Deak <imre.deak at intel.com>
CC: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_gem.c | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index dff8d05d80ee..50fd611926cb 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2201,6 +2201,15 @@ unlock:
 	mutex_unlock(&obj->mm.lock);
 }
 
+static unsigned long swiotlb_max_size(void)
+{
+#if IS_ENABLED(CONFIG_SWIOTLB)
+	return swiotlb_nr_tbl() << IO_TLB_SHIFT;
+#else
+	return 0;
+#endif
+}
+
 static struct sg_table *
 i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 {
@@ -2212,6 +2221,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 	struct sgt_iter sgt_iter;
 	struct page *page;
 	unsigned long last_pfn = 0;	/* suppress gcc warning */
+	unsigned long max_segment;
 	int ret;
 	gfp_t gfp;
 
@@ -2222,6 +2232,10 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 	GEM_BUG_ON(obj->base.read_domains & I915_GEM_GPU_DOMAINS);
 	GEM_BUG_ON(obj->base.write_domain & I915_GEM_GPU_DOMAINS);
 
+	max_segment = swiotlb_max_size();
+	if (!max_segment)
+		max_segment = obj->base.size;
+
 	st = kmalloc(sizeof(*st), GFP_KERNEL);
 	if (st == NULL)
 		return ERR_PTR(-ENOMEM);
@@ -2263,15 +2277,9 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 				goto err_pages;
 			}
 		}
-#ifdef CONFIG_SWIOTLB
-		if (swiotlb_nr_tbl()) {
-			st->nents++;
-			sg_set_page(sg, page, PAGE_SIZE, 0);
-			sg = sg_next(sg);
-			continue;
-		}
-#endif
-		if (!i || page_to_pfn(page) != last_pfn + 1) {
+		if (!i ||
+		    sg->length >= max_segment ||
+		    page_to_pfn(page) != last_pfn + 1) {
 			if (i)
 				sg = sg_next(sg);
 			st->nents++;
@@ -2284,9 +2292,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 		/* Check that the i965g/gm workaround works. */
 		WARN_ON((gfp & __GFP_DMA32) && (last_pfn >= 0x00100000UL));
 	}
-#ifdef CONFIG_SWIOTLB
-	if (!swiotlb_nr_tbl())
-#endif
+	if (sg) /* loop terminated early; short sg table */
 		sg_mark_end(sg);
 
 	ret = i915_gem_gtt_prepare_pages(obj, st);
-- 
2.9.3