linux-kernel - Re: [PATCH v4 3/8] mfd: syscon: Add reference counting and device managed support

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Message-ID: <CAHp75VfKXEyHF25xRq8EDp5SeBdyPHLgzw=4s1xkjer=sNu7aw@mail.gmail.com>
Date: Mon, 5 Aug 2024 22:20:56 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Herve Codina <herve.codina@...tlin.com>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>, Simon Horman <horms@...nel.org>, Lee Jones <lee@...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 v4 3/8] mfd: syscon: Add reference counting and device
 managed support

On Mon, Aug 5, 2024 at 12:19 PM Herve Codina <herve.codina@...tlin.com> 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

retrieves?

> 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.

...

> -       if (!syscon)
> +       if (!syscon) {
>                 syscon = of_syscon_register(np, check_res);
> +               if (IS_ERR(syscon))
> +                       return ERR_CAST(syscon);
> +       } else {
> +               syscon_get(syscon);
> +       }

  if (syscon)
    return syscon_get();

?

> +       return syscon;

...

> +static struct regmap *__devm_syscon_get(struct device *dev,
> +                                       struct syscon *syscon)
> +{
> +       struct syscon **ptr;
> +
> +       if (IS_ERR(syscon))
> +               return ERR_CAST(syscon);
> +
> +       ptr = devres_alloc(devm_syscon_release, sizeof(struct syscon *), GFP_KERNEL);
> +       if (!ptr) {
> +               syscon_put(syscon);
> +               return ERR_PTR(-ENOMEM);
> +       }
> +
> +       *ptr = syscon;
> +       devres_add(dev, ptr);
> +
> +       return syscon->regmap;

Can't the devm_add_action_or_reset() be used in this case? If so,
perhaps a comment to explain why?

> +}

-- 
With Best Regards,
Andy Shevchenko