regmap: add flat cache with sparse validity

The flat regcache will always assume the data in the cache is valid.
Since the cache is preferred over hardware access, this may shadow the
actual state of the device.

Add a new containing cache structure with the flat data table and a
bitmap indicating cache validity. REGCACHE_FLAT will still behave as
before, as the validity is ignored.

Define new cache type REGCACHE_FLAT_S: a flat cache with sparse
validity. The sparse validity is used to determine if a hardware access
should occur to initialize the cache on the fly, vs. at regmap init for
REGCACHE_FLAT. Contrary to REGCACHE_FLAT, this allows us to implement
regcache_ops.drop.

Signed-off-by: Sander Vanheule <sander@svanheule.net>
Link: https://patch.msgid.link/20251029081248.52607-2-sander@svanheule.net
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 91 insertions, 11 deletions

diff --git a/drivers/base/regmap/regcache-flat.c b/drivers/base/regmap/regcache-flat.c
index f36d3618b67c..86f7679175b1 100644
--- a/drivers/base/regmap/regcache-flat.c
+++ b/drivers/base/regmap/regcache-flat.c
@@ -6,7 +6,11 @@
 //
 // Author: Mark Brown <broonie@opensource.wolfsonmicro.com>
 
+#include <linux/bitmap.h>
+#include <linux/bitops.h>
 #include <linux/device.h>
+#include <linux/limits.h>
+#include <linux/overflow.h>
 #include <linux/seq_file.h>
 #include <linux/slab.h>
 
@@ -18,34 +22,62 @@ static inline unsigned int regcache_flat_get_index(const struct regmap *map,
 	return regcache_get_index_by_order(map, reg);
 }
 
+struct regcache_flat_data {
+	unsigned long *valid;
+	unsigned int data[];
+};
+
 static int regcache_flat_init(struct regmap *map)
 {
 	int i;
-	unsigned int *cache;
+	size_t cache_data_size;
+	unsigned int cache_size;
+	struct regcache_flat_data *cache;
 
 	if (!map || map->reg_stride_order < 0 || !map->max_register_is_set)
 		return -EINVAL;
 
-	map->cache = kcalloc(regcache_flat_get_index(map, map->max_register)
-			     + 1, sizeof(unsigned int), map->alloc_flags);
-	if (!map->cache)
+	cache_size = regcache_flat_get_index(map, map->max_register) + 1;
+	cache_data_size = struct_size(cache, data, cache_size);
+
+	if (cache_data_size == SIZE_MAX) {
+		dev_err(map->dev, "cannot allocate regmap cache");
 		return -ENOMEM;
+	}
 
-	cache = map->cache;
+	cache = kzalloc(cache_data_size, map->alloc_flags);
+	if (!cache)
+		return -ENOMEM;
+
+	cache->valid = bitmap_zalloc(cache_size, map->alloc_flags);
+	if (!cache->valid)
+		goto err_free;
+
+	map->cache = cache;
 
 	for (i = 0; i < map->num_reg_defaults; i++) {
 		unsigned int reg = map->reg_defaults[i].reg;
 		unsigned int index = regcache_flat_get_index(map, reg);
 
-		cache[index] = map->reg_defaults[i].def;
+		cache->data[index] = map->reg_defaults[i].def;
+		__set_bit(index, cache->valid);
 	}
 
 	return 0;
+
+err_free:
+	kfree(cache);
+	return -ENOMEM;
 }
 
 static int regcache_flat_exit(struct regmap *map)
 {
-	kfree(map->cache);
+	struct regcache_flat_data *cache = map->cache;
+
+	if (cache)
+		bitmap_free(cache->valid);
+
+	kfree(cache);
 	map->cache = NULL;
 
 	return 0;
@@ -54,10 +86,24 @@ static int regcache_flat_exit(struct regmap *map)
 static int regcache_flat_read(struct regmap *map,
 			      unsigned int reg, unsigned int *value)
 {
-	unsigned int *cache = map->cache;
+	struct regcache_flat_data *cache = map->cache;
 	unsigned int index = regcache_flat_get_index(map, reg);
 
-	*value = cache[index];
+	*value = cache->data[index];
+
+	return 0;
+}
+
+static int regcache_flat_sparse_read(struct regmap *map,
+				     unsigned int reg, unsigned int *value)
+{
+	struct regcache_flat_data *cache = map->cache;
+	unsigned int index = regcache_flat_get_index(map, reg);
+
+	if (unlikely(!test_bit(index, cache->valid)))
+		return -ENOENT;
+
+	*value = cache->data[index];
 
 	return 0;
 }
@@ -65,10 +111,34 @@ static int regcache_flat_read(struct regmap *map,
 static int regcache_flat_write(struct regmap *map, unsigned int reg,
 			       unsigned int value)
 {
-	unsigned int *cache = map->cache;
+	struct regcache_flat_data *cache = map->cache;
 	unsigned int index = regcache_flat_get_index(map, reg);
 
-	cache[index] = value;
+	cache->data[index] = value;
+
+	return 0;
+}
+
+static int regcache_flat_sparse_write(struct regmap *map, unsigned int reg,
+				      unsigned int value)
+{
+	struct regcache_flat_data *cache = map->cache;
+	unsigned int index = regcache_flat_get_index(map, reg);
+
+	cache->data[index] = value;
+	__set_bit(index, cache->valid);
+
+	return 0;
+}
+
+static int regcache_flat_drop(struct regmap *map, unsigned int min,
+			      unsigned int max)
+{
+	struct regcache_flat_data *cache = map->cache;
+	unsigned int bitmap_min = regcache_flat_get_index(map, min);
+	unsigned int bitmap_max = regcache_flat_get_index(map, max);
+
+	bitmap_clear(cache->valid, bitmap_min, bitmap_max + 1 - bitmap_min);
 
 	return 0;
 }
@@ -81,3 +151,13 @@ struct regcache_ops regcache_flat_ops = {
 	.read = regcache_flat_read,
 	.write = regcache_flat_write,
 };
+
+struct regcache_ops regcache_flat_sparse_ops = {
+	.type = REGCACHE_FLAT_S,
+	.name = "flat-sparse",
+	.init = regcache_flat_init,
+	.exit = regcache_flat_exit,
+	.read = regcache_flat_sparse_read,
+	.write = regcache_flat_sparse_write,
+	.drop = regcache_flat_drop,
+};