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, 5 insertions, 4 deletions

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 55cdb4d30a1..984a0c5fbf5 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -464,7 +464,7 @@ init_pipe_control(struct intel_ring_buffer *ring)
 		goto err_unref;
 
 	pc->gtt_offset = obj->gtt_offset;
-	pc->cpu_page =  kmap(obj->pages[0]);
+	pc->cpu_page =  kmap(sg_page(obj->pages->sgl));
 	if (pc->cpu_page == NULL)
 		goto err_unpin;
 
@@ -491,7 +491,8 @@ cleanup_pipe_control(struct intel_ring_buffer *ring)
 		return;
 
 	obj = pc->obj;
-	kunmap(obj->pages[0]);
+
+	kunmap(sg_page(obj->pages->sgl));
 	i915_gem_object_unpin(obj);
 	drm_gem_object_unreference(&obj->base);
 
@@ -1026,7 +1027,7 @@ static void cleanup_status_page(struct intel_ring_buffer *ring)
 	if (obj == NULL)
 		return;
 
-	kunmap(obj->pages[0]);
+	kunmap(sg_page(obj->pages->sgl));
 	i915_gem_object_unpin(obj);
 	drm_gem_object_unreference(&obj->base);
 	ring->status_page.obj = NULL;
@@ -1053,7 +1054,7 @@ static int init_status_page(struct intel_ring_buffer *ring)
 	}
 
 	ring->status_page.gfx_addr = obj->gtt_offset;
-	ring->status_page.page_addr = kmap(obj->pages[0]);
+	ring->status_page.page_addr = kmap(sg_page(obj->pages->sgl));
 	if (ring->status_page.page_addr == NULL) {
 		ret = -ENOMEM;
 		goto err_unpin;