lib/debugfs: Add igt_assert_crc_equal

Because of hash collisions tests should only ever compare crc
checksums for equality. Checking for inequality can result in random
failures.

To ensure this only expose and igt_assert function and use that.
Follow-up patches will rework the code for tests which don't follow
this requirement and try to compare for CRC inequality.

v2: Rebase on top of Matt's kms_plane changes.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

lib/igt_debugfs.c

@@ -63,7 +63,7 @@
  * another either for equality or difference. Otherwise CRCs must be treated as
  * completely opaque values. Note that not even CRCs from different pipes or tap
  * points on the same platform can be compared. Hence only use igt_crc_is_null()
- * and igt_crc_equal() to inspect CRC values captured by the same
+ * and igt_assert_crc_equal() to inspect CRC values captured by the same
  * #igt_pipe_crc_t object.
  *
  * # Other debugfs interface wrappers
@@ -234,6 +234,25 @@ bool igt_crc_equal(igt_crc_t *a, igt_crc_t *b)
 	return true;
 }
 
+/**
+ * igt_assert_crc_equal:
+ * @a: first pipe CRC value
+ * @b: second pipe CRC value
+ *
+ * Compares two CRC values and fails the testcase if they don't match with
+ * igt_fail(). Note that due to CRC collisions CRC based testcase can only
+ * assert that CRCs match, never that they are different. Otherwise there might
+ * be random testcase failures when different screen contents end up with the
+ * same CRC by chance.
+ */
+void igt_assert_crc_equal(igt_crc_t *a, igt_crc_t *b)
+{
+	int i;
+
+	for (i = 0; i < a->n_words; i++)
+		igt_assert_eq_u32(a->crc[i], b->crc[i]);
+}
+
 /**
  * igt_crc_to_string:
  * @crc: pipe CRC value to print

lib/igt_debugfs.h

@@ -87,6 +87,7 @@ enum intel_pipe_crc_source {
 
 bool igt_crc_is_null(igt_crc_t *crc);
 bool igt_crc_equal(igt_crc_t *a, igt_crc_t *b);
+void igt_assert_crc_equal(igt_crc_t *a, igt_crc_t *b);
 char *igt_crc_to_string(igt_crc_t *crc);
 
 void igt_require_pipe_crc(void);