linux-kernel - [PATCH v2] regmap: Add debugfs file for forcing field writes

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Message-ID: <pnd1qifa7sj.fsf@axis.com>
Date:   Tue, 13 Jun 2023 13:42:27 +0200
From:   Waqar Hameed <waqar.hameed@...s.com>
To:     Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
CC:     <kernel@...s.com>, <linux-kernel@...r.kernel.org>
Subject: [PATCH v2] 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@...s.com>
---
Changes in v2:
* Add macro to guard the debugfs entry.
* Fix `Signed-off-by` in commit message to match actual email address.
* Link to v1: https://lore.kernel.org/all/pndttvcu3ut.fsf@axis.com/

 drivers/base/regmap/internal.h       |  3 +++
 drivers/base/regmap/regmap-debugfs.c | 11 +++++++++++
 drivers/base/regmap/regmap.c         |  2 +-
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/base/regmap/internal.h b/drivers/base/regmap/internal.h
index 9bd0dfd1e259..6472b3222b82 100644
--- a/drivers/base/regmap/internal.h
+++ b/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;
diff --git a/drivers/base/regmap/regmap-debugfs.c b/drivers/base/regmap/regmap-debugfs.c
index c491fabe3617..f36027591e1a 100644
--- a/drivers/base/regmap/regmap-debugfs.c
+++ b/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);
diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index fa2d3fba6ac9..89b701ceb43f 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -3273,7 +3273,7 @@ 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;

base-commit: 858fd168a95c5b9669aac8db6c14a9aeab446375
-- 
2.30.2