Re: [PATCH 0/3] ASoC: cs35l41/cs35l45/cs4265: sort the reg_defaults tables

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

On 05/08/2026 11:40, Pierre-Louis Bossart wrote:
> 
>> reg_defaults must be sorted by ascending register address as
>> regcache_lookup_reg() locates the entries in it with bsearch(), see commit
>> fd80df352ba1 ("regcache: Add support for sorting defaults arrays").
>>
>> These three tables have entries which are out of order, so the binary search
>> does not find part of them.  For those registers regcache_reg_needs_sync()
>> cannot compare the cached value against the default and reports that a sync
>> is needed, so they are written to the device on every regcache_sync() even
>> when they were never touched.
>>
>> The patches only reorder the existing entries, the text of every entry is
>> kept verbatim and no default value is changed.  Each table was verified by
>> evaluating the register addresses and replaying lib/bsearch.c on them.
>>
>> Entries not reachable by the binary search, per table:
>>
>>   cs35l41_reg           2 (of 47)
>>   cs35l45_defaults     36 (of 73)
>>   cs4265_reg_defaults   3 (of 16)
>>
>> For cs35l45 this is nearly half of the table: the DSP1_RX*_RATE and
>> DSP1_TX*_RATE registers sit in the middle of it while their addresses are
>> far above everything else, which cuts the search off from the whole
>> 0x4c40 - 0xf010 range.
>>
>> Found by an audit of all reg_defaults tables under sound/, the SoundWire
>> codec drivers are fixed by a separate series.
> 
> Wow. Would it make sense to have a regmap helper to double-check the
> addresses are indeed in-order in those reg_default tables?
> I am not sure how this requirement can be enforced by just inspection, a
> warning would help detect this sort of issues on more platforms.


I had this first:
diff --git a/drivers/base/regmap/regcache.c b/drivers/base/regmap/regcache.c
index be167ee6f57c..7d2f74494645 100644
--- a/drivers/base/regmap/regcache.c
+++ b/drivers/base/regmap/regcache.c
@@ -187,6 +187,9 @@ int regcache_init(struct regmap *map, const struct
regmap_config *config)
 		if (!tmp_buf)
 			return -ENOMEM;
 		map->reg_defaults = tmp_buf;
+
+		/* regcache_lookup_reg() bsearch()es this array */
+		regcache_sort_defaults(tmp_buf, map->num_reg_defaults);
 	} else if (map->num_reg_defaults_raw) {
 		count = regcache_count_cacheable_registers(map);
 		if (!count)


But it would run for all regmap on boot and I think that would be a big
hit on boot time.
I guess, a debug kernel option could enable ordering check for defaults
in regmap and warn if it finds such?

-- 
Péter