drm/i915: handle walking compact dma scatter lists

So far the assumption was that each dma scatter list entry contains only
a single page. This might not hold in the future, when we'll introduce
compact scatter lists, so prepare for this everywhere in the i915 code
where we walk such a list.

We'll fix the place _creating_ these lists separately in the next patch
to help the reviewing/bisectability.

Reference: http://www.spinics.net/lists/dri-devel/msg33917.html
Signed-off-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1528,17 +1528,12 @@ void i915_gem_lastclose(struct drm_device *dev);
 int __must_check i915_gem_object_get_pages(struct drm_i915_gem_object *obj);
 static inline struct page *i915_gem_object_get_page(struct drm_i915_gem_object *obj, int n)
 {
-	struct scatterlist *sg = obj->pages->sgl;
-	int nents = obj->pages->nents;
-	while (nents > SG_MAX_SINGLE_ALLOC) {
-		if (n < SG_MAX_SINGLE_ALLOC - 1)
-			break;
-
-		sg = sg_chain_ptr(sg + SG_MAX_SINGLE_ALLOC - 1);
-		n -= SG_MAX_SINGLE_ALLOC - 1;
-		nents -= SG_MAX_SINGLE_ALLOC - 1;
-	}
-	return sg_page(sg+n);
+	struct sg_page_iter sg_iter;
+
+	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents, n)
+		return sg_iter.page;
+
+	return NULL;
 }
 static inline void i915_gem_object_pin_pages(struct drm_i915_gem_object *obj)
 {

drivers/gpu/drm/i915/i915_gem.c

@@ -411,8 +411,7 @@ i915_gem_shmem_pread(struct drm_device *dev,
 	int obj_do_bit17_swizzling, page_do_bit17_swizzling;
 	int prefaulted = 0;
 	int needs_clflush = 0;
-	struct scatterlist *sg;
-	int i;
+	struct sg_page_iter sg_iter;
 
 	user_data = to_user_ptr(args->data_ptr);
 	remain = args->size;
@@ -441,11 +440,9 @@ i915_gem_shmem_pread(struct drm_device *dev,
 
 	offset = args->offset;
 
-	for_each_sg(obj->pages->sgl, sg, obj->pages->nents, i) {
-		struct page *page;
-
-		if (i < offset >> PAGE_SHIFT)
-			continue;
+	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents,
+			 offset >> PAGE_SHIFT) {
+		struct page *page = sg_iter.page;
 
 		if (remain <= 0)
 			break;
@@ -460,7 +457,6 @@ i915_gem_shmem_pread(struct drm_device *dev,
 		if ((shmem_page_offset + page_length) > PAGE_SIZE)
 			page_length = PAGE_SIZE - shmem_page_offset;
 
-		page = sg_page(sg);
 		page_do_bit17_swizzling = obj_do_bit17_swizzling &&
 			(page_to_phys(page) & (1 << 17)) != 0;
 
@@ -732,8 +728,7 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
 	int hit_slowpath = 0;
 	int needs_clflush_after = 0;
 	int needs_clflush_before = 0;
-	int i;
-	struct scatterlist *sg;
+	struct sg_page_iter sg_iter;
 
 	user_data = to_user_ptr(args->data_ptr);
 	remain = args->size;
@@ -768,13 +763,11 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
 	offset = args->offset;
 	obj->dirty = 1;
 
-	for_each_sg(obj->pages->sgl, sg, obj->pages->nents, i) {
-		struct page *page;
+	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents,
+			 offset >> PAGE_SHIFT) {
+		struct page *page = sg_iter.page;
 		int partial_cacheline_write;
 
-		if (i < offset >> PAGE_SHIFT)
-			continue;
-
 		if (remain <= 0)
 			break;
 
@@ -796,7 +789,6 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
 			((shmem_page_offset | page_length)
 				& (boot_cpu_data.x86_clflush_size - 1));
 
-		page = sg_page(sg);
 		page_do_bit17_swizzling = obj_do_bit17_swizzling &&
 			(page_to_phys(page) & (1 << 17)) != 0;
 

drivers/gpu/drm/i915/i915_gem_dmabuf.c

@@ -62,7 +62,7 @@ static struct sg_table *i915_gem_map_dma_buf(struct dma_buf_attachment *attachme
 	src = obj->pages->sgl;
 	dst = st->sgl;
 	for (i = 0; i < obj->pages->nents; i++) {
-		sg_set_page(dst, sg_page(src), PAGE_SIZE, 0);
+		sg_set_page(dst, sg_page(src), src->length, 0);
 		dst = sg_next(dst);
 		src = sg_next(src);
 	}
@@ -105,7 +105,7 @@ static void *i915_gem_dmabuf_vmap(struct dma_buf *dma_buf)
 {
 	struct drm_i915_gem_object *obj = dma_buf->priv;
 	struct drm_device *dev = obj->base.dev;
-	struct scatterlist *sg;
+	struct sg_page_iter sg_iter;
 	struct page **pages;
 	int ret, i;
 
@@ -124,14 +124,15 @@ static void *i915_gem_dmabuf_vmap(struct dma_buf *dma_buf)
 
 	ret = -ENOMEM;
 
-	pages = drm_malloc_ab(obj->pages->nents, sizeof(struct page *));
+	pages = drm_malloc_ab(obj->base.size >> PAGE_SHIFT, sizeof(*pages));
 	if (pages == NULL)
 		goto error;
 
-	for_each_sg(obj->pages->sgl, sg, obj->pages->nents, i)
-		pages[i] = sg_page(sg);
+	i = 0;
+	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents, 0);
+		pages[i++] = sg_iter.page;
 
-	obj->dma_buf_vmapping = vmap(pages, obj->pages->nents, 0, PAGE_KERNEL);
+	obj->dma_buf_vmapping = vmap(pages, i, 0, PAGE_KERNEL);
 	drm_free_large(pages);
 
 	if (!obj->dma_buf_vmapping)

drivers/gpu/drm/i915/i915_gem_tiling.c

@@ -473,28 +473,29 @@ i915_gem_swizzle_page(struct page *page)
 void
 i915_gem_object_do_bit_17_swizzle(struct drm_i915_gem_object *obj)
 {
-	struct scatterlist *sg;
-	int page_count = obj->base.size >> PAGE_SHIFT;
+	struct sg_page_iter sg_iter;
 	int i;
 
 	if (obj->bit_17 == NULL)
 		return;
 
-	for_each_sg(obj->pages->sgl, sg, page_count, i) {
-		struct page *page = sg_page(sg);
+	i = 0;
+	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents, 0) {
+		struct page *page = sg_iter.page;
 		char new_bit_17 = page_to_phys(page) >> 17;
 		if ((new_bit_17 & 0x1) !=
 		    (test_bit(i, obj->bit_17) != 0)) {
 			i915_gem_swizzle_page(page);
 			set_page_dirty(page);
 		}
+		i++;
 	}
 }
 
 void
 i915_gem_object_save_bit_17_swizzle(struct drm_i915_gem_object *obj)
 {
-	struct scatterlist *sg;
+	struct sg_page_iter sg_iter;
 	int page_count = obj->base.size >> PAGE_SHIFT;
 	int i;
 
@@ -508,11 +509,12 @@ i915_gem_object_save_bit_17_swizzle(struct drm_i915_gem_object *obj)
 		}
 	}
 
-	for_each_sg(obj->pages->sgl, sg, page_count, i) {
-		struct page *page = sg_page(sg);
-		if (page_to_phys(page) & (1 << 17))
+	i = 0;
+	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents, 0) {
+		if (page_to_phys(sg_iter.page) & (1 << 17))
 			__set_bit(i, obj->bit_17);
 		else
 			__clear_bit(i, obj->bit_17);
+		i++;
 	}
 }