Since 0 can look a lot like a NULL pointer when used in a cache some clever
data structures might potentially introduce bugs specific to handling it.
Add some explicit testing of storing 0 as a value in a sparse cache, at the
minute there are no issues and this will stop any appearing in the future.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 drivers/base/regmap/regmap-kunit.c | 43 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/drivers/base/regmap/regmap-kunit.c b/drivers/base/regmap/regmap-kunit.c
index d790c7df5cac..64df047d9d53 100644
--- a/drivers/base/regmap/regmap-kunit.c
+++ b/drivers/base/regmap/regmap-kunit.c
@@ -1486,6 +1486,48 @@ static void cache_present(struct kunit *test)
 		KUNIT_ASSERT_TRUE(test, regcache_reg_cached(map, param->from_reg + i));
 }
 
+static void cache_write_zero(struct kunit *test)
+{
+	const struct regmap_test_param *param = test->param_value;
+	struct regmap *map;
+	struct regmap_config config;
+	struct regmap_ram_data *data;
+	unsigned int val;
+	int i;
+
+	config = test_regmap_config;
+
+	map = gen_regmap(test, &config, &data);
+	KUNIT_ASSERT_FALSE(test, IS_ERR(map));
+	if (IS_ERR(map))
+		return;
+
+	for (i = 0; i < BLOCK_TEST_SIZE; i++)
+		data->read[param->from_reg + i] = false;
+
+	/* No defaults so no registers cached. */
+	for (i = 0; i < BLOCK_TEST_SIZE; i++)
+		KUNIT_ASSERT_FALSE(test, regcache_reg_cached(map, param->from_reg + i));
+
+	/* We didn't trigger any reads */
+	for (i = 0; i < BLOCK_TEST_SIZE; i++)
+		KUNIT_ASSERT_FALSE(test, data->read[param->from_reg + i]);
+
+	/* Write a zero value */
+	KUNIT_EXPECT_EQ(test, 0, regmap_write(map, 1, 0));
+
+	/* Read that zero value back */
+	KUNIT_EXPECT_EQ(test, 0, regmap_read(map, 1, &val));
+	KUNIT_EXPECT_EQ(test, 0, val);
+
+	/* From the cache? */
+	KUNIT_ASSERT_TRUE(test, regcache_reg_cached(map, 1));
+
+	/* Try to throw it away */
+	KUNIT_EXPECT_EQ(test, 0, regcache_drop_region(map, 1, 1));
+	KUNIT_ASSERT_FALSE(test, regcache_reg_cached(map, 1));
+}
+
 /* Check that caching the window register works with sync */
 static void cache_range_window_reg(struct kunit *test)
 {
@@ -1999,6 +2041,7 @@ static struct kunit_case regmap_test_cases[] = {
 	KUNIT_CASE_PARAM(cache_drop_all_and_sync_no_defaults, sparse_cache_types_gen_params),
 	KUNIT_CASE_PARAM(cache_drop_all_and_sync_has_defaults, sparse_cache_types_gen_params),
 	KUNIT_CASE_PARAM(cache_present, sparse_cache_types_gen_params),
+	KUNIT_CASE_PARAM(cache_write_zero, sparse_cache_types_gen_params),
 	KUNIT_CASE_PARAM(cache_range_window_reg, real_cache_types_only_gen_params),
 
 	KUNIT_CASE_PARAM(raw_read_defaults_single, raw_test_types_gen_params),

---
base-commit: 98f7e32f20d28ec452afb208f9cffc08448a2652
change-id: 20240923-regcache-zero-value-d95494d1f70e

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

On Tue, 24 Sep 2024 12:08:53 +0200, Mark Brown wrote:
> Since 0 can look a lot like a NULL pointer when used in a cache some clever
> data structures might potentially introduce bugs specific to handling it.
> Add some explicit testing of storing 0 as a value in a sparse cache, at the
> minute there are no issues and this will stop any appearing in the future.
> 
> 

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regmap.git for-next

Thanks!

[1/1] regmap: Specifically test writing 0 as a value to sparse caches
      commit: 42afe80caff040525252af6e9601287777d144fe

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark