[PATCH] regmap: do not call regmap_debugfs_init() from regmap_attach_dev()

From: Matthias Schiffer
Date: Mon Jul 26 2021 - 03:37:32 EST

regmap_debugfs_init() should never be called twice for the same regmap,
as it initializes various fields of the regmap struct, including list
heads and mutices. A visible symptom are messages like:

debugfs: Directory 'dummy-iomuxc-gpr@20e4000' with parent 'regmap'
already present!

This happened whenever regmap_attach_dev() was called for an existing
regmap. Remove the call from regmap_attach_dev() and change
__regmap_init() so that regmap_debugfs_init() is called exactly once.

Signed-off-by: Matthias Schiffer <matthias.schiffer@xxxxxxxxxxxxxxx>
Fixes: 9b947a13e7f6 ("regmap: use debugfs even when no device")
drivers/base/regmap/regmap.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

As mentioned in my previous mail [1], I believe that the duplicate call to
regmap_debugfs_init() is not the only issue with regmap_attach_dev().

Every single user of regmap_attach_dev() outside of __regmap_init() is
using it to attach a device to a syscon regmap obtained using one of the
syscon_*() functions. AIUI, syscon regmaps do not belong to a single
device, so calling regmap_attach_dev() seems wrong to me. My (possibly
lacking) understanding of the semantics aside, the fact that
regmap_attach_dev() is setting fields on the shared regmap without any
kind of locking is at least suspicious.

Maybe regmap_attach_dev() shouldn't be exported from the regmap code at
all, removing all calls to the functions from drivers?

[1] https://lkml.org/lkml/2021/7/19/500

diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index fe3e38dd5324..27625a1330ac 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -630,8 +630,6 @@ int regmap_attach_dev(struct device *dev, struct regmap *map,
if (ret)
return ret;

- regmap_debugfs_init(map);
/* Add a devres resource for dev_get_regmap() */
m = devres_alloc(dev_get_regmap_release, sizeof(*m), GFP_KERNEL);
if (!m) {
@@ -1192,10 +1190,10 @@ struct regmap *__regmap_init(struct device *dev,
ret = regmap_attach_dev(dev, map, config);
if (ret != 0)
goto err_regcache;
- } else {
- regmap_debugfs_init(map);

+ regmap_debugfs_init(map);
return map;