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, 25 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c
index 3dbc7f17eb11..4a4274b348b6 100644
--- a/drivers/gpu/drm/drm_cache.c
+++ b/drivers/gpu/drm/drm_cache.c
@@ -101,6 +101,31 @@ drm_clflush_pages(struct page *pages[], unsigned long num_pages)
 EXPORT_SYMBOL(drm_clflush_pages);
 
 void
+drm_clflush_sg(struct sg_table *st)
+{
+#if defined(CONFIG_X86)
+	if (cpu_has_clflush) {
+		struct scatterlist *sg;
+		int i;
+
+		mb();
+		for_each_sg(st->sgl, sg, st->nents, i)
+			drm_clflush_page(sg_page(sg));
+		mb();
+
+		return;
+	}
+
+	if (on_each_cpu(drm_clflush_ipi_handler, NULL, 1) != 0)
+		printk(KERN_ERR "Timed out waiting for cache flush.\n");
+#else
+	printk(KERN_ERR "Architecture has no drm_cache.c support\n");
+	WARN_ON_ONCE(1);
+#endif
+}
+EXPORT_SYMBOL(drm_clflush_sg);
+
+void
 drm_clflush_virt_range(char *addr, unsigned long length)
 {
 #if defined(CONFIG_X86)