drm/selftests: add drm buddy alloc limit testcase

add a test to check the maximum allocation limit

v2(Matthew Auld):
- added err = -EINVAL in block NULL check
- removed unnecessary test succeeded print

Signed-off-by: Arunpravin <[e-mail]>
Reviewed-by: Matthew Auld <[e-mail]>
Acked-by: Christian König <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Signed-off-by: Christian König <[e-mail]>

drivers/gpu/drm/selftests/drm_buddy_selftests.h

···
  * Tests are executed in order by igt/drm_buddy
  */
 selftest(sanitycheck, igt_sanitycheck) /* keep first (selfcheck for igt) */
+selftest(buddy_alloc_limit, igt_buddy_alloc_limit)

drivers/gpu/drm/selftests/test-drm_buddy.c

···
 
 static unsigned int random_seed;
 
+static int igt_buddy_alloc_limit(void *arg)
+{
+	u64 end, size = U64_MAX, start = 0;
+	struct drm_buddy_block *block;
+	unsigned long flags = 0;
+	LIST_HEAD(allocated);
+	struct drm_buddy mm;
+	int err;
+
+	size = end = round_down(size, 4096);
+	err = drm_buddy_init(&mm, size, PAGE_SIZE);
+	if (err)
+		return err;
+
+	if (mm.max_order != DRM_BUDDY_MAX_ORDER) {
+		pr_err("mm.max_order(%d) != %d\n",
+		       mm.max_order, DRM_BUDDY_MAX_ORDER);
+		err = -EINVAL;
+		goto out_fini;
+	}
+
+	err = drm_buddy_alloc_blocks(&mm, start, end, size,
+				     PAGE_SIZE, &allocated, flags);
+
+	if (unlikely(err))
+		goto out_free;
+
+	block = list_first_entry_or_null(&allocated,
+					 struct drm_buddy_block,
+					 link);
+
+	if (!block) {
+		err = -EINVAL;
+		goto out_fini;
+	}
+
+	if (drm_buddy_block_order(block) != mm.max_order) {
+		pr_err("block order(%d) != %d\n",
+		       drm_buddy_block_order(block), mm.max_order);
+		err = -EINVAL;
+		goto out_free;
+	}
+
+	if (drm_buddy_block_size(&mm, block) !=
+	    BIT_ULL(mm.max_order) * PAGE_SIZE) {
+		pr_err("block size(%llu) != %llu\n",
+		       drm_buddy_block_size(&mm, block),
+		       BIT_ULL(mm.max_order) * PAGE_SIZE);
+		err = -EINVAL;
+		goto out_free;
+	}
+
+out_free:
+	drm_buddy_free_list(&mm, &allocated);
+out_fini:
+	drm_buddy_fini(&mm);
+	return err;
+}
+
 static int igt_sanitycheck(void *ignored)
 {
 	pr_info("%s - ok!\n", __func__);