Hi Lee,

On Tue, 3 Sep 2024 16:38:39 +0100
Lee Jones [off-list ref] wrote:

On Thu, 08 Aug 2024, Herve Codina wrote:

quoted

From: Clément Léger <clement.leger@bootlin.com>

Syscon releasing is not supported.
Without release function, unbinding a driver that uses syscon whether
explicitly or due to a module removal left the used syscon in a in-use
state.

For instance a syscon_node_to_regmap() call from a consumer retrieves a
syscon regmap instance. Internally, syscon_node_to_regmap() can create
syscon instance and add it to the existing syscon list. No API is
available to release this syscon instance, remove it from the list and
free it when it is not used anymore.

Introduce reference counting in syscon in order to keep track of syscon
usage using syscon_{get,put}() and add a device managed version of
syscon_regmap_lookup_by_phandle(), to automatically release the syscon
instance on the consumer removal.

Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
---
 drivers/mfd/syscon.c       | 138 ++++++++++++++++++++++++++++++++++---
 include/linux/mfd/syscon.h |  16 +++++
 2 files changed, 144 insertions(+), 10 deletions(-)  

This doesn't look very popular.

What are the potential ramifications for existing users?

Existing user don't use devm_syscon_regmap_lookup_by_phandle() nor
syscon_put_regmap().

So refcount is incremented but never decremented. syscon is never
released. Exactly the same as current implementation.
Nothing change for existing users.

Best regards,
Hervé