linux-kernel - Re: [PATCH 01/17] mfd: syscon: Add reference counting and device managed support

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Date: Tue, 30 Apr 2024 21:34:43 +0100
From: Simon Horman <horms@...nel.org>
To: Herve Codina <herve.codina@...tlin.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Lee Jones <lee@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Horatiu Vultur <horatiu.vultur@...rochip.com>,
	UNGLinuxDriver@...rochip.com, Andrew Lunn <andrew@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Saravana Kannan <saravanak@...gle.com>,
	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>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	netdev@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.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 01/17] mfd: syscon: Add reference counting and device
 managed support

On Tue, Apr 30, 2024 at 10:37:10AM +0200, 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 retrieve 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>

..

> diff --git a/include/linux/mfd/syscon.h b/include/linux/mfd/syscon.h
> index c315903f6dab..164b9bcb49c3 100644
> --- a/include/linux/mfd/syscon.h
> +++ b/include/linux/mfd/syscon.h
> @@ -15,6 +15,7 @@
>  #include <linux/errno.h>
>  
>  struct device_node;
> +struct device;
>  
>  #ifdef CONFIG_MFD_SYSCON
>  struct regmap *device_node_to_regmap(struct device_node *np);
> @@ -28,6 +29,11 @@ struct regmap *syscon_regmap_lookup_by_phandle_args(struct device_node *np,
>  						    unsigned int *out_args);
>  struct regmap *syscon_regmap_lookup_by_phandle_optional(struct device_node *np,
>  							const char *property);
> +void syscon_put_regmap(struct regmap *regmap);
> +
> +struct regmap *devm_syscon_regmap_lookup_by_phandle(struct device *dev,
> +						    struct device_node *np,
> +						    const char *property);
>  #else
>  static inline struct regmap *device_node_to_regmap(struct device_node *np)
>  {
> @@ -67,6 +73,18 @@ static inline struct regmap *syscon_regmap_lookup_by_phandle_optional(
>  	return NULL;
>  }
>  
> +static intline void syscon_put_regmap(struct regmap *regmap)

intline -> inline

> +{
> +}

..