drm/i915: Replace the array of pages with a scatterlist

Rather than have multiple data structures for describing our page layout
in conjunction with the array of pages, we can migrate all users over to
a scatterlist.

One major advantage, other than unifying the page tracking structures,
this offers is that we replace the vmalloc'ed array (which can be up to
a megabyte in size) with a chain of individual pages which helps reduce
memory pressure.

The disadvantage is that we then do not have a simple array to iterate,
or to access randomly. The common case for this is in the relocation
processing, which will typically fit within a single scatterlist page
and so be almost the same cost as the simple array. For iterating over
the array, the extra function call could be optimised away, but in
reality is an insignificant cost of either binding the pages, or
performing the pwrite/pread.

v2: Fix drm_clflush_sg() to not invoke wbinvd as well! And fix the
trivial compile error from rebasing.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 11 insertions, 7 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 12a075747dc..1d7502faebd 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1006,16 +1006,11 @@ struct drm_i915_gem_object {
 
 	unsigned int has_aliasing_ppgtt_mapping:1;
 	unsigned int has_global_gtt_mapping:1;
+	unsigned int has_dma_mapping:1;
 
-	struct page **pages;
+	struct sg_table *pages;
 	int pages_pin_count;
 
-	/**
-	 * DMAR support
-	 */
-	struct scatterlist *sg_list;
-	int num_sg;
-
 	/* prime dma-buf support */
 	struct sg_table *sg_table;
 	void *dma_buf_vmapping;
@@ -1342,6 +1337,15 @@ void i915_gem_release_mmap(struct drm_i915_gem_object *obj);
 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;
+	while (n >= SG_MAX_SINGLE_ALLOC) {
+		sg = sg_chain_ptr(sg + SG_MAX_SINGLE_ALLOC - 1);
+		n -= SG_MAX_SINGLE_ALLOC - 1;
+	}
+	return sg_page(sg+n);
+}
 static inline void i915_gem_object_pin_pages(struct drm_i915_gem_object *obj)
 {
 	BUG_ON(obj->pages == NULL);