[PATCH v3] 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, there
are other tests which should have similar verification that we actually
changed something.

While we're at it refactor the test to use three changed values rather
than attempting to use one of them twice, that just complicates checking
that our new values are actually new.

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 v3:
- Use 3 separate test values rather than attempting to reuse one of them
  for raw and regular writes.
- Link to v2: https://lore.kernel.org/r/20240209-regmap-kunit-random-change-v2-1-be0a447c2891@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 | 54 +++++++++++++++++++++++++++-----------
 1 file changed, 38 insertions(+), 16 deletions(-)

diff --git a/drivers/base/regmap/regmap-kunit.c b/drivers/base/regmap/regmap-kunit.c
index 026bdcb45127..3da34ed1412a 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,
@@ -1251,7 +1268,7 @@ static void raw_sync(struct kunit *test)
 	struct regmap *map;
 	struct regmap_config config;
 	struct regmap_ram_data *data;
-	u16 val[2];
+	u16 val[3];
 	u16 *hw_buf;
 	unsigned int rval;
 	int i;
@@ -1265,17 +1282,13 @@ static void raw_sync(struct kunit *test)
 
 	hw_buf = (u16 *)data->vals;
 
-	get_random_bytes(&val, sizeof(val));
+	get_changed_bytes(&hw_buf[2], &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,
-						      be16_to_cpu(val[0])));
-	else
-		KUNIT_EXPECT_EQ(test, 0, regmap_write(map, 6,
-						      le16_to_cpu(val[0])));
+	KUNIT_EXPECT_EQ(test, 0, regmap_raw_write(map, 2, val,
+						  sizeof(u16) * 2));
+	KUNIT_EXPECT_EQ(test, 0, regmap_write(map, 4, val[2]));
 
 	/* We should read back the new values, and defaults for the rest */
 	for (i = 0; i < config.max_register + 1; i++) {
@@ -1284,24 +1297,34 @@ static void raw_sync(struct kunit *test)
 		switch (i) {
 		case 2:
 		case 3:
-		case 6:
 			if (config.val_format_endian == REGMAP_ENDIAN_BIG) {
 				KUNIT_EXPECT_EQ(test, rval,
-						be16_to_cpu(val[i % 2]));
+						be16_to_cpu(val[i - 2]));
 			} else {
 				KUNIT_EXPECT_EQ(test, rval,
-						le16_to_cpu(val[i % 2]));
+						le16_to_cpu(val[i - 2]));
 			}
 			break;
+		case 4:
+			KUNIT_EXPECT_EQ(test, rval, val[i - 2]);
+			break;
 		default:
 			KUNIT_EXPECT_EQ(test, config.reg_defaults[i].def, rval);
 			break;
 		}
 	}
+
+	/*
+	 * The value written via _write() was translated by the core,
+	 * translate the original copy for comparison purposes.
+	 */
+	if (config.val_format_endian == REGMAP_ENDIAN_BIG)
+		val[2] = cpu_to_be16(val[2]);
+	else
+		val[2] = cpu_to_le16(val[2]);
 	
 	/* 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[2], &val[0], sizeof(val));
 
 	for (i = 0; i < config.max_register + 1; i++)
 		data->written[i] = false;
@@ -1312,8 +1335,7 @@ static void raw_sync(struct kunit *test)
 	KUNIT_EXPECT_EQ(test, 0, regcache_sync(map));
 
 	/* 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[2], &val[0], sizeof(val));
 
 	regmap_exit(map);
 }

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

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