[PATCH v2] regmap: kunit: Ensure that changed bytes are actually different

[Mark Brown <broonie@kernel.org>]

During the cache sync test we verify that values we expect to have been
written only to the cache do not appear in the hardware. This works most
of the time but since we randomly generate both the original and new values
there is a low probability that these values may actually be the same.
Wrap get_random_bytes() to ensure that the values are different, it is
likely we will want a similar pattern for other tests in the future.

We use random generation to try to avoid data dependencies in the tests.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
Changes in v2:
- Check the whole change in.
- Link to v1: https://lore.kernel.org/r/20240209-regmap-kunit-random-change-v1-1-ad2d76757583@kernel.org
---
 drivers/base/regmap/regmap-kunit.c | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/drivers/base/regmap/regmap-kunit.c b/drivers/base/regmap/regmap-kunit.c
index 026bdcb45127..e149b12d0d4a 100644
--- a/drivers/base/regmap/regmap-kunit.c
+++ b/drivers/base/regmap/regmap-kunit.c
@@ -9,6 +9,23 @@
 
 #define BLOCK_TEST_SIZE 12
 
+static void get_changed_bytes(void *orig, void *new, size_t size)
+{
+	char *o = orig;
+	char *n = new;
+	int i;
+
+	get_random_bytes(new, size);
+
+	/*
+	 * This could be nicer and more efficient but we shouldn't
+	 * super care.
+	 */
+	for (i = 0; i < size; i++)
+		while (n[i] == o[i])
+			get_random_bytes(&n[i], 1);
+}
+
 static const struct regmap_config test_regmap_config = {
 	.max_register = BLOCK_TEST_SIZE,
 	.reg_stride = 1,
@@ -1265,16 +1282,16 @@ static void raw_sync(struct kunit *test)
 
 	hw_buf = (u16 *)data->vals;
 
-	get_random_bytes(&val, sizeof(val));
+	get_changed_bytes(&hw_buf[6], &val[0], sizeof(val));
 
 	/* Do a regular write and a raw write in cache only mode */
 	regcache_cache_only(map, true);
 	KUNIT_EXPECT_EQ(test, 0, regmap_raw_write(map, 2, val, sizeof(val)));
 	if (config.val_format_endian == REGMAP_ENDIAN_BIG)
-		KUNIT_EXPECT_EQ(test, 0, regmap_write(map, 6,
+		KUNIT_EXPECT_EQ(test, 0, regmap_write(map, 4,
 						      be16_to_cpu(val[0])));
 	else
-		KUNIT_EXPECT_EQ(test, 0, regmap_write(map, 6,
+		KUNIT_EXPECT_EQ(test, 0, regmap_write(map, 4,
 						      le16_to_cpu(val[0])));
 
 	/* We should read back the new values, and defaults for the rest */
@@ -1284,7 +1301,7 @@ static void raw_sync(struct kunit *test)
 		switch (i) {
 		case 2:
 		case 3:
-		case 6:
+		case 4:
 			if (config.val_format_endian == REGMAP_ENDIAN_BIG) {
 				KUNIT_EXPECT_EQ(test, rval,
 						be16_to_cpu(val[i % 2]));
@@ -1301,7 +1318,7 @@ static void raw_sync(struct kunit *test)
 	
 	/* The values should not appear in the "hardware" */
 	KUNIT_EXPECT_MEMNEQ(test, &hw_buf[2], val, sizeof(val));
-	KUNIT_EXPECT_MEMNEQ(test, &hw_buf[6], val, sizeof(u16));
+	KUNIT_EXPECT_MEMNEQ(test, &hw_buf[4], val, sizeof(u16));
 
 	for (i = 0; i < config.max_register + 1; i++)
 		data->written[i] = false;
@@ -1313,7 +1330,7 @@ static void raw_sync(struct kunit *test)
 
 	/* The values should now appear in the "hardware" */
 	KUNIT_EXPECT_MEMEQ(test, &hw_buf[2], val, sizeof(val));
-	KUNIT_EXPECT_MEMEQ(test, &hw_buf[6], val, sizeof(u16));
+	KUNIT_EXPECT_MEMEQ(test, &hw_buf[4], val, sizeof(u16));
 
 	regmap_exit(map);
 }

---
base-commit: 3b201c9af7c0cad2e8311d96c0c1b399606c70fa
change-id: 20240209-regmap-kunit-random-change-178bd19b91b5

Best regards,
-- 
Mark Brown <broonie@kernel.org>