regmap: Add test that writes to write only registers are prevented

We should have error checking that verifies that writes to write only
registers are suppressed, verify that this happens as it should.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230613-regmap-kunit-read-write-v1-1-2db337c52827@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: broonie

drivers/base/regmap/regmap-kunit.c

@@ -92,6 +92,11 @@ static struct regmap *gen_regmap(struct regmap_config *config,
 	return ret;
 }
 
+static bool reg_5_false(struct device *context, unsigned int reg)
+{
+	return reg != 5;
+}
+
 static void basic_read_write(struct kunit *test)
 {
 	struct regcache_types *t = (struct regcache_types *)test->param_value;
@@ -191,6 +196,41 @@ static void bulk_read(struct kunit *test)
 	regmap_exit(map);
 }
 
+static void write_readonly(struct kunit *test)
+{
+	struct regcache_types *t = (struct regcache_types *)test->param_value;
+	struct regmap *map;
+	struct regmap_config config;
+	struct regmap_ram_data *data;
+	unsigned int val;
+	int i;
+
+	config = test_regmap_config;
+	config.cache_type = t->type;
+	config.num_reg_defaults = BLOCK_TEST_SIZE;
+	config.writeable_reg = reg_5_false;
+
+	map = gen_regmap(&config, &data);
+	KUNIT_ASSERT_FALSE(test, IS_ERR(map));
+	if (IS_ERR(map))
+		return;
+
+	get_random_bytes(&val, sizeof(val));
+
+	for (i = 0; i < BLOCK_TEST_SIZE; i++)
+		data->written[i] = false;
+
+	/* Change the value of all registers, readonly should fail */
+	for (i = 0; i < BLOCK_TEST_SIZE; i++)
+		KUNIT_EXPECT_EQ(test, i != 5, regmap_write(map, i, val) == 0);
+
+	/* Did that match what we see on the device? */
+	for (i = 0; i < BLOCK_TEST_SIZE; i++)
+		KUNIT_EXPECT_EQ(test, i != 5, data->written[i]);
+
+	regmap_exit(map);
+}
+
 static void reg_defaults(struct kunit *test)
 {
 	struct regcache_types *t = (struct regcache_types *)test->param_value;
@@ -1037,6 +1077,7 @@ static struct kunit_case regmap_test_cases[] = {
 	KUNIT_CASE_PARAM(basic_read_write, regcache_types_gen_params),
 	KUNIT_CASE_PARAM(bulk_write, regcache_types_gen_params),
 	KUNIT_CASE_PARAM(bulk_read, regcache_types_gen_params),
+	KUNIT_CASE_PARAM(write_readonly, regcache_types_gen_params),
 	KUNIT_CASE_PARAM(reg_defaults, regcache_types_gen_params),
 	KUNIT_CASE_PARAM(reg_defaults_read_dev, regcache_types_gen_params),
 	KUNIT_CASE_PARAM(register_patch, regcache_types_gen_params),