Re: [PATCH v4 01/11] firmware: raspberrypi: Keep count of all consumers

From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Florian Fainelli" <f.fainelli@gmail.com>,
	"Ray Jui" <rjui@broadcom.com>,
	"Scott Branden" <sbranden@broadcom.com>,
	bcm-kernel-feedback-list <bcm-kernel-feedback-list@broadcom.com>,
	linux-pwm@vger.kernel.org,
	"linux-arm Mailing List" <linux-arm-kernel@lists.infradead.org>,
	devicetree <devicetree@vger.kernel.org>,
	"Stefan Wahren" <wahrenst@gmx.net>,
	linux-input <linux-input@vger.kernel.org>,
	"Dmitry Torokhov" <dmitry.torokhov@gmail.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"open list:STAGING SUBSYSTEM" <devel@driverdev.osuosl.org>,
	"Philipp Zabel" <p.zabel@pengutronix.de>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	linux-clk <linux-clk@vger.kernel.org>,
	"Stephen Boyd" <sboyd@kernel.org>,
	linux-rpi-kernel <linux-rpi-kernel@lists.infradead.org>,
	"Bartosz Golaszewski" <bgolaszewski@baylibre.com>
Subject: Re: [PATCH v4 01/11] firmware: raspberrypi: Keep count of all consumers
Date: Thu, 12 Nov 2020 19:52:14 +0200	[thread overview]
Message-ID: <CAHp75Vf9E7UWVDMs=eRjLjoSN6SVOWw9thNdnR8ruCL6GmY7JQ@mail.gmail.com> (raw)
In-Reply-To: <20201112163630.17177-2-nsaenzjulienne@suse.de>

On Thu, Nov 12, 2020 at 6:40 PM Nicolas Saenz Julienne
<nsaenzjulienne@suse.de> wrote:
>
> When unbinding the firmware device we need to make sure it has no
> consumers left. Otherwise we'd leave them with a firmware handle
> pointing at freed memory.
>
> Keep a reference count of all consumers and introduce rpi_firmware_put()
> which will permit automatically decrease the reference count upon
> unbinding consumer drivers.

...

>  /**
> - * rpi_firmware_get - Get pointer to rpi_firmware structure.
>   * @firmware_node:    Pointer to the firmware Device Tree node.
>   *
> + * The reference to rpi_firmware has to be released with rpi_firmware_put().
> + *
>   * Returns NULL is the firmware device is not ready.
>   */
>  struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node)
>  {
>         struct platform_device *pdev = of_find_device_by_node(firmware_node);
> +       struct rpi_firmware *fw;
>
>         if (!pdev)
>                 return NULL;
>
> -       return platform_get_drvdata(pdev);
> +       fw = platform_get_drvdata(pdev);
> +       if (!fw)
> +               return NULL;
> +
> +       if (!kref_get_unless_zero(&fw->consumers))
> +               return NULL;

Don't we have a more traditional way of doing this, i.e.
try_module_get() coupled with get_device() ?

> +       return fw;
>  }

-- 
With Best Regards,
Andy Shevchenko