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

From: Herve Codina <[email-masked]>
Date: Mon, 9 Sep 2024 09:52:03 +0200

Hi Lee, Arnd,

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

> 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

I hope I answered to Lee's question related to possible impacts on
existing drivers.

Is there anything else that blocks this patch from being applied ?

Best regards,
Hervé