Subject: Re: [PATCH v5 3/8] mfd: syscon: Add reference counting and device managed support

From: Herve Codina <[email-masked]>
Date: Tue, 3 Sep 2024 18:01:16 +0200

Hi Lee,

On Tue, 3 Sep 2024 16:38:39 +0100
Lee Jones <[email-masked]> wrote:

> On Thu, 08 Aug 2024, Herve Codina wrote:
> 
> > From: Clément Léger <[email-masked]>
> > 
> > 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 <[email-masked]>
> > Signed-off-by: Herve Codina <[email-masked]>
> > ---
> >  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