drm/i915: Fix DMA mapped scatterlist lookup

As the previous patch fixed the places where we walk the whole scatterlist
for DMA addresses, this patch fixes the random lookup functionality.

To achieve this we have to add a second lookup iterator and add a
i915_gem_object_get_sg_dma helper, to be used analoguous to existing
i915_gem_object_get_sg_dma. Therefore two lookup caches are maintained per
object and they are flushed at the same point for simplicity. (Strictly
speaking the DMA cache should be flushed from i915_gem_gtt_finish_pages,
but today this conincides with unsetting of the pages in general.)

Partial VMA view is then fixed to use the new DMA lookup and properly
query sg length.

v2:
 * Checkpatch.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Tom Murphy <murphyt7@tcd.ie>
Cc: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20201006092508.1064287-2-tvrtko.ursulin@linux.intel.com

drivers/gpu/drm/i915/gem/i915_gem_object.c

@@ -73,6 +73,8 @@ void i915_gem_object_init(struct drm_i915_gem_object *obj,
 	obj->mm.madv = I915_MADV_WILLNEED;
 	INIT_RADIX_TREE(&obj->mm.get_page.radix, GFP_KERNEL | __GFP_NOWARN);
 	mutex_init(&obj->mm.get_page.lock);
+	INIT_RADIX_TREE(&obj->mm.get_dma_page.radix, GFP_KERNEL | __GFP_NOWARN);
+	mutex_init(&obj->mm.get_dma_page.lock);
 
 	if (IS_ENABLED(CONFIG_LOCKDEP) && i915_gem_object_is_shrinkable(obj))
 		i915_gem_shrinker_taints_mutex(to_i915(obj->base.dev),

drivers/gpu/drm/i915/gem/i915_gem_object.h

@@ -275,8 +275,26 @@ int i915_gem_object_set_tiling(struct drm_i915_gem_object *obj,
 			       unsigned int tiling, unsigned int stride);
 
 struct scatterlist *
+__i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
+			 struct i915_gem_object_page_iter *iter,
+			 unsigned int n,
+			 unsigned int *offset);
+
+static inline struct scatterlist *
 i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
-		       unsigned int n, unsigned int *offset);
+		       unsigned int n,
+		       unsigned int *offset)
+{
+	return __i915_gem_object_get_sg(obj, &obj->mm.get_page, n, offset);
+}
+
+static inline struct scatterlist *
+i915_gem_object_get_sg_dma(struct drm_i915_gem_object *obj,
+			   unsigned int n,
+			   unsigned int *offset)
+{
+	return __i915_gem_object_get_sg(obj, &obj->mm.get_dma_page, n, offset);
+}
 
 struct page *
 i915_gem_object_get_page(struct drm_i915_gem_object *obj,

drivers/gpu/drm/i915/gem/i915_gem_object_types.h

@@ -80,6 +80,14 @@ struct i915_mmap_offset {
 	struct rb_node offset;
 };
 
+struct i915_gem_object_page_iter {
+	struct scatterlist *sg_pos;
+	unsigned int sg_idx; /* in pages, but 32bit eek! */
+
+	struct radix_tree_root radix;
+	struct mutex lock; /* protects this cache */
+};
+
 struct drm_i915_gem_object {
 	struct drm_gem_object base;
 
@@ -246,13 +254,8 @@ struct drm_i915_gem_object {
 
 		I915_SELFTEST_DECLARE(unsigned int page_mask);
 
-		struct i915_gem_object_page_iter {
-			struct scatterlist *sg_pos;
-			unsigned int sg_idx; /* in pages, but 32bit eek! */
-
-			struct radix_tree_root radix;
-			struct mutex lock; /* protects this cache */
-		} get_page;
+		struct i915_gem_object_page_iter get_page;
+		struct i915_gem_object_page_iter get_dma_page;
 
 		/**
 		 * Element within i915->mm.unbound_list or i915->mm.bound_list,

drivers/gpu/drm/i915/gem/i915_gem_pages.c

@@ -33,6 +33,8 @@ void __i915_gem_object_set_pages(struct drm_i915_gem_object *obj,
 
 	obj->mm.get_page.sg_pos = pages->sgl;
 	obj->mm.get_page.sg_idx = 0;
+	obj->mm.get_dma_page.sg_pos = pages->sgl;
+	obj->mm.get_dma_page.sg_idx = 0;
 
 	obj->mm.pages = pages;
 
@@ -155,6 +157,8 @@ static void __i915_gem_object_reset_page_iter(struct drm_i915_gem_object *obj)
 	rcu_read_lock();
 	radix_tree_for_each_slot(slot, &obj->mm.get_page.radix, &iter, 0)
 		radix_tree_delete(&obj->mm.get_page.radix, iter.index);
+	radix_tree_for_each_slot(slot, &obj->mm.get_dma_page.radix, &iter, 0)
+		radix_tree_delete(&obj->mm.get_dma_page.radix, iter.index);
 	rcu_read_unlock();
 }
 
@@ -450,11 +454,12 @@ void __i915_gem_object_release_map(struct drm_i915_gem_object *obj)
 }
 
 struct scatterlist *
-i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
-		       unsigned int n,
-		       unsigned int *offset)
+__i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
+			 struct i915_gem_object_page_iter *iter,
+			 unsigned int n,
+			 unsigned int *offset)
 {
-	struct i915_gem_object_page_iter *iter = &obj->mm.get_page;
+	const bool dma = iter == &obj->mm.get_dma_page;
 	struct scatterlist *sg;
 	unsigned int idx, count;
 
@@ -483,7 +488,7 @@ i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
 
 	sg = iter->sg_pos;
 	idx = iter->sg_idx;
-	count = __sg_page_count(sg);
+	count = dma ? __sg_dma_page_count(sg) : __sg_page_count(sg);
 
 	while (idx + count <= n) {
 		void *entry;
@@ -511,7 +516,7 @@ i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
 
 		idx += count;
 		sg = ____sg_next(sg);
-		count = __sg_page_count(sg);
+		count = dma ? __sg_dma_page_count(sg) : __sg_page_count(sg);
 	}
 
 scan:
@@ -529,7 +534,7 @@ i915_gem_object_get_sg(struct drm_i915_gem_object *obj,
 	while (idx + count <= n) {
 		idx += count;
 		sg = ____sg_next(sg);
-		count = __sg_page_count(sg);
+		count = dma ? __sg_dma_page_count(sg) : __sg_page_count(sg);
 	}
 
 	*offset = n - idx;
@@ -582,7 +587,7 @@ i915_gem_object_get_dma_address_len(struct drm_i915_gem_object *obj,
 	struct scatterlist *sg;
 	unsigned int offset;
 
-	sg = i915_gem_object_get_sg(obj, n, &offset);
+	sg = i915_gem_object_get_sg_dma(obj, n, &offset);
 
 	if (len)
 		*len = sg_dma_len(sg) - (offset << PAGE_SHIFT);

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

@@ -1383,15 +1383,15 @@ intel_partial_pages(const struct i915_ggtt_view *view,
 	if (ret)
 		goto err_sg_alloc;
 
-	iter = i915_gem_object_get_sg(obj, view->partial.offset, &offset);
+	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(iter->length - (offset << PAGE_SHIFT),
+		len = min(sg_dma_len(iter) - (offset << PAGE_SHIFT),
 			  count << PAGE_SHIFT);
 		sg_set_page(sg, NULL, len, 0);
 		sg_dma_address(sg) =

drivers/gpu/drm/i915/i915_scatterlist.h

@@ -48,6 +48,11 @@ static inline int __sg_page_count(const struct scatterlist *sg)
 	return sg->length >> PAGE_SHIFT;
 }
 
+static inline int __sg_dma_page_count(const struct scatterlist *sg)
+{
+	return sg_dma_len(sg) >> PAGE_SHIFT;
+}
+
 static inline struct scatterlist *____sg_next(struct scatterlist *sg)
 {
 	++sg;