drm/i915/selftests: mix huge pages

Try to mix sg page sizes for 4K, 64K and 2M pages.

v2: s/BIT(x) >> 12/BIT(x) >> PAGE_SHIFT/

Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171006145041.21673-19-matthew.auld@intel.com
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171006221833.32439-18-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/selftests/scatterlist.c

@@ -189,6 +189,20 @@ static unsigned int random(unsigned long n,
 	return 1 + (prandom_u32_state(rnd) % 1024);
 }
 
+static unsigned int random_page_size_pages(unsigned long n,
+					   unsigned long count,
+					   struct rnd_state *rnd)
+{
+	/* 4K, 64K, 2M */
+	static unsigned int page_count[] = {
+		BIT(12) >> PAGE_SHIFT,
+		BIT(16) >> PAGE_SHIFT,
+		BIT(21) >> PAGE_SHIFT,
+	};
+
+	return page_count[(prandom_u32_state(rnd) % 3)];
+}
+
 static inline bool page_contiguous(struct page *first,
 				   struct page *last,
 				   unsigned long npages)
@@ -252,6 +266,7 @@ static const npages_fn_t npages_funcs[] = {
 	grow,
 	shrink,
 	random,
+	random_page_size_pages,
 	NULL,
 };