regmap: maple: Implement block sync for the maple tree cache

For register maps where we can write multiple values in a single bus
operation it is generally much faster to do so. Improve the performance of
maple tree cache syncs on such devices by identifying blocks of adjacent
registers that need to be written out and combining them into a single
operation.

Combining writes does mean that we need to allocate a scratch buffer and
format the data into it but it is expected that for most cases where caches
are in use the cost of I/O will be much greater than the cost of doing the
allocation and format.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230609-regcache-maple-sync-raw-v1-1-8ddeb4e2b9ab@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: broonie

drivers/base/regmap/internal.h

@@ -257,6 +257,8 @@ int regcache_sync_block(struct regmap *map, void *block,
 			unsigned long *cache_present,
 			unsigned int block_base, unsigned int start,
 			unsigned int end);
+bool regcache_reg_needs_sync(struct regmap *map, unsigned int reg,
+			     unsigned int val);
 
 static inline const void *regcache_get_val_addr(struct regmap *map,
 						const void *base,

drivers/base/regmap/regcache-maple.c

@@ -186,6 +186,55 @@ static int regcache_maple_drop(struct regmap *map, unsigned int min,
 	return ret;
 }
 
+static int regcache_maple_sync_block(struct regmap *map, unsigned long *entry,
+				     struct ma_state *mas,
+				     unsigned int min, unsigned int max)
+{
+	void *buf;
+	unsigned long r;
+	size_t val_bytes = map->format.val_bytes;
+	int ret = 0;
+
+	mas_pause(mas);
+	rcu_read_unlock();
+
+	/*
+	 * Use a raw write if writing more than one register to a
+	 * device that supports raw writes to reduce transaction
+	 * overheads.
+	 */
+	if (max - min > 1 && regmap_can_raw_write(map)) {
+		buf = kmalloc(val_bytes * (max - min), map->alloc_flags);
+		if (!buf) {
+			ret = -ENOMEM;
+			goto out;
+		}
+
+		/* Render the data for a raw write */
+		for (r = min; r < max; r++) {
+			regcache_set_val(map, buf, r - min,
+					 entry[r - mas->index]);
+		}
+
+		ret = _regmap_raw_write(map, min, buf, (max - min) * val_bytes,
+					false);
+
+		kfree(buf);
+	} else {
+		for (r = min; r < max; r++) {
+			ret = _regmap_write(map, r,
+					    entry[r - mas->index]);
+			if (ret != 0)
+				goto out;
+		}
+	}
+
+out:
+	rcu_read_lock();
+
+	return ret;
+}
+
 static int regcache_maple_sync(struct regmap *map, unsigned int min,
 			       unsigned int max)
 {
@@ -194,27 +243,48 @@ static int regcache_maple_sync(struct regmap *map, unsigned int min,
 	MA_STATE(mas, mt, min, max);
 	unsigned long lmin = min;
 	unsigned long lmax = max;
-	unsigned int r;
+	unsigned int r, v, sync_start;
 	int ret;
+	bool sync_needed = false;
 
 	map->cache_bypass = true;
 
 	rcu_read_lock();
 
 	mas_for_each(&mas, entry, max) {
 		for (r = max(mas.index, lmin); r <= min(mas.last, lmax); r++) {
-			mas_pause(&mas);
-			rcu_read_unlock();
-			ret = regcache_sync_val(map, r, entry[r - mas.index]);
+			v = entry[r - mas.index];
+
+			if (regcache_reg_needs_sync(map, r, v)) {
+				if (!sync_needed) {
+					sync_start = r;
+					sync_needed = true;
+				}
+				continue;
+			}
+
+			if (!sync_needed)
+				continue;
+
+			ret = regcache_maple_sync_block(map, entry, &mas,
+							sync_start, r);
 			if (ret != 0)
 				goto out;
-			rcu_read_lock();
+			sync_needed = false;
+		}
+
+		if (sync_needed) {
+			ret = regcache_maple_sync_block(map, entry, &mas,
+							sync_start, r);
+			if (ret != 0)
+				goto out;
+			sync_needed = false;
 		}
 	}
 
+out:
 	rcu_read_unlock();
 
-out:
 	map->cache_bypass = false;
 
 	return ret;

drivers/base/regmap/regcache.c

@@ -279,8 +279,8 @@ int regcache_write(struct regmap *map,
 	return 0;
 }
 
-static bool regcache_reg_needs_sync(struct regmap *map, unsigned int reg,
-				    unsigned int val)
+bool regcache_reg_needs_sync(struct regmap *map, unsigned int reg,
+			     unsigned int val)
 {
 	int ret;