[PATCH] regcache: Sort the local copy of an unsorted reg_defaults array

[Peter Ujfalusi <peter.ujfalusi@linux.intel.com>]

regcache_lookup_reg() bsearch()es the reg_defaults array, which requires
it to be sorted by ascending register address.  Entries following a
descending step are never found, so regcache_reg_needs_sync() reports
that they need a sync and they are written to the device on every
regcache_sync() even when they were never touched.

Detect the misordering while reg_defaults is validated against the
register stride and sort the local copy.  The check needs no new loop
and sort() only runs for the affected drivers, which are also warned
about.

Note that sort() is not stable, so for arrays with duplicated register
addresses it remains unspecified which entry is found.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
---
Hi,

Fixes for affected in-tree codec drivers have been posted separately, so this
is meant as a safety net for out-of-tree and future drivers rather than a
replacement for fixing them, as discussed on the Cirrus codec patches.

I'm not sure about the print level: dev_warn() makes the problem visible to
whoever boots the affected machine, but the person who can act on it is the
driver author.  Should this be dev_dbg()?

Regards,
Peter

 drivers/base/regmap/regcache.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/base/regmap/regcache.c b/drivers/base/regmap/regcache.c
index be167ee6f57c..aa7f6c30f232 100644
--- a/drivers/base/regmap/regcache.c
+++ b/drivers/base/regmap/regcache.c
@@ -123,6 +123,8 @@ static void regcache_hw_exit(struct regmap *map)
 
 int regcache_init(struct regmap *map, const struct regmap_config *config)
 {
+	bool sort_defaults = false;
+	unsigned int reg_prev = 0;
 	int count = 0;
 	int ret;
 	int i;
@@ -149,10 +151,16 @@ int regcache_init(struct regmap *map, const struct regmap_config *config)
 		return -EINVAL;
 	}
 
-	for (i = 0; i < config->num_reg_defaults; i++)
+	for (i = 0; i < config->num_reg_defaults; i++) {
 		if (config->reg_defaults[i].reg % map->reg_stride)
 			return -EINVAL;
 
+		if (reg_prev > config->reg_defaults[i].reg)
+			sort_defaults = true;
+
+		reg_prev = config->reg_defaults[i].reg;
+	}
+
 	for (i = 0; i < ARRAY_SIZE(cache_types); i++)
 		if (cache_types[i]->type == map->cache_type)
 			break;
@@ -186,6 +194,13 @@ int regcache_init(struct regmap *map, const struct regmap_config *config)
 					sizeof(*map->reg_defaults), GFP_KERNEL);
 		if (!tmp_buf)
 			return -ENOMEM;
+
+		/* regcache_lookup_reg() bsearch()es this array */
+		if (sort_defaults) {
+			dev_warn(map->dev,
+				 "Driver needs fixing: Unsorted reg_defaults, sorting the copy\n");
+			regcache_sort_defaults(tmp_buf, map->num_reg_defaults);
+		}
 		map->reg_defaults = tmp_buf;
 	} else if (map->num_reg_defaults_raw) {
 		count = regcache_count_cacheable_registers(map);
-- 
2.55.0