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

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Message-ID: <20240912143740.GD24460@google.com>
Date: Thu, 12 Sep 2024 15:37:40 +0100
From: Lee Jones <lee@...nel.org>
To: Herve Codina <herve.codina@...tlin.com>, Arnd Bergmann <arnd@...db.de>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	Simon Horman <horms@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Derek Kiernan <derek.kiernan@....com>,
	Dragan Cvetic <dragan.cvetic@....com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Lars Povlsen <lars.povlsen@...rochip.com>,
	Steen Hegelund <Steen.Hegelund@...rochip.com>,
	Daniel Machon <daniel.machon@...rochip.com>,
	UNGLinuxDriver@...rochip.com, Rob Herring <robh@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Horatiu Vultur <horatiu.vultur@...rochip.com>,
	Andrew Lunn <andrew@...n.ch>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	Allan Nielsen <allan.nielsen@...rochip.com>,
	Luca Ceresoli <luca.ceresoli@...tlin.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	Clément Léger <clement.leger@...tlin.com>
Subject: Re: [PATCH v5 3/8] mfd: syscon: Add reference counting and device
 managed support

On Mon, 09 Sep 2024, Herve Codina wrote:

> Hi Lee, Arnd,
> 
> On Tue, 3 Sep 2024 18:01:16 +0200
> Herve Codina <herve.codina@...tlin.com> wrote:
> 
> > Hi Lee,
> > 
> > On Tue, 3 Sep 2024 16:38:39 +0100
> > Lee Jones <lee@...nel.org> wrote:
> > 
> > > On Thu, 08 Aug 2024, Herve Codina wrote:
> > >   
> > > > From: Clément Léger <clement.leger@...tlin.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@...tlin.com>
> > > > Signed-off-by: Herve Codina <herve.codina@...tlin.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
> 
> 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 ?

Arnd usually takes care of Syscon reviews.

Perhaps he's out on vacation.

Let's wait a little longer, since it's too late for this cycle anyway.

-- 
Lee Jones [李琼斯]