regmap: Add debugfs file for forcing field writes

`_regmap_update_bits()` checks if the current register value differs
from the new value, and only writes to the register if they differ. When
testing hardware drivers, it might be desirable to always force a
register write, for example when writing to a `regmap_field`. This
enables and simplifies testing and verification of the hardware
interaction. For example, when using a hardware mock/simulation model,
one can then more easily verify that the driver makes the correct
expected register writes during certain events.

Add a bool variable `force_write_field` and a corresponding debugfs
entry to enable this. Since this feature could interfere with driver
operation, guard it with a macro.
Signed-off-by: Waqar Hameed <waqar.hameed@axis.com>
Link: https://lore.kernel.org/r/pnd1qifa7sj.fsf@axis.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/base/regmap/internal.h

@@ -125,6 +125,9 @@ struct regmap {
 	int reg_stride;
 	int reg_stride_order;
 
+	/* If set, will always write field to HW. */
+	bool force_write_field;
+
 	/* regcache specific members */
 	const struct regcache_ops *cache_ops;
 	enum regcache_type cache_type;

drivers/base/regmap/regmap-debugfs.c

@@ -636,6 +636,17 @@ void regmap_debugfs_init(struct regmap *map)
 				    &regmap_cache_bypass_fops);
 	}
 
+	/*
+	 * This could interfere with driver operation. Therefore, don't provide
+	 * any real compile time configuration option for this feature. One will
+	 * have to modify the source code directly in order to use it.
+	 */
+#undef REGMAP_ALLOW_FORCE_WRITE_FIELD_DEBUGFS
+#ifdef REGMAP_ALLOW_FORCE_WRITE_FIELD_DEBUGFS
+	debugfs_create_bool("force_write_field", 0600, map->debugfs,
+			    &map->force_write_field);
+#endif
+
 	next = rb_first(&map->range_tree);
 	while (next) {
 		range_node = rb_entry(next, struct regmap_range_node, node);

drivers/base/regmap/regmap.c

@@ -3279,7 +3279,7 @@ static int _regmap_update_bits(struct regmap *map, unsigned int reg,
 		tmp = orig & ~mask;
 		tmp |= val & mask;
 
-		if (force_write || (tmp != orig)) {
+		if (force_write || (tmp != orig) || map->force_write_field) {
 			ret = _regmap_write(map, reg, tmp);
 			if (ret == 0 && change)
 				*change = true;