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

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Date:   Thu, 12 Nov 2020 19:52:14 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        linux-pwm@...r.kernel.org,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        Stefan Wahren <wahrenst@....net>,
        linux-input <linux-input@...r.kernel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:STAGING SUBSYSTEM" <devel@...verdev.osuosl.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        linux-rpi-kernel <linux-rpi-kernel@...ts.infradead.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH v4 01/11] firmware: raspberrypi: Keep count of all consumers

On Thu, Nov 12, 2020 at 6:40 PM Nicolas Saenz Julienne
<nsaenzjulienne@...e.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