linux-kernel - Re: [PATCH 1/2] drivers: create a pin control subsystem v7

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Date:	Tue, 27 Sep 2011 11:30:08 +0200
From:	Stijn Devriendt <highguy@...il.com>
To:	Linus Walleij <linus.walleij@...ricsson.com>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Grant Likely <grant.likely@...retlab.ca>,
	Stephen Warren <swarren@...dia.com>,
	Barry Song <21cnbao@...il.com>,
	Lee Jones <lee.jones@...aro.org>,
	Joe Perches <joe@...ches.com>,
	Russell King <linux@....linux.org.uk>,
	Linaro Dev <linaro-dev@...ts.linaro.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	David Brown <davidb@...eaurora.org>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH 1/2] drivers: create a pin control subsystem v7

> +static int pin_request(struct pinctrl_dev *pctldev,
> +                      int pin, const char *function, bool gpio,
> +                      struct pinctrl_gpio_range *gpio_range)
> +{
> +       struct pin_desc *desc;
> +       const struct pinmux_ops *ops = pctldev->desc->pmxops;
> +       int status = -EINVAL;
> +
> +       dev_dbg(&pctldev->dev, "request pin %d for %s\n", pin, function);
> +
> +       if (!pin_is_valid(pctldev, pin)) {
> +               dev_err(&pctldev->dev, "pin is invalid\n");
> +               return -EINVAL;
> +       }
> +
> +       if (!function) {
> +               dev_err(&pctldev->dev, "no function name given\n");
> +               return -EINVAL;
> +       }
> +
> +       desc = pin_desc_get(pctldev, pin);
> +       if (desc == NULL) {
> +               dev_err(&pctldev->dev,
> +                       "pin is not registered so it cannot be requested\n");
> +               goto out;
> +       }
> +
> +       spin_lock(&desc->lock);
> +       if (desc->mux_requested) {
> +               spin_unlock(&desc->lock);
> +               dev_err(&pctldev->dev,
> +                       "pin already requested\n");
> +               goto out;
> +       }
> +       spin_unlock(&desc->lock);

Now this is racing with...

> +
> +       /* Let each pin increase references to this module */
> +       if (!try_module_get(pctldev->owner)) {
> +               dev_err(&pctldev->dev,
> +                       "could not increase module refcount for pin %d\n",
> +                       pin);
> +               status = -EINVAL;
> +               goto out;
> +       }
> +
> +       /*
> +        * If there is no kind of request function for the pin we just assume
> +        * we got it by default and proceed.
> +        */
> +       if (gpio && ops->gpio_request_enable)
> +               /* This requests and enables a single GPIO pin */
> +               status = ops->gpio_request_enable(pctldev, gpio_range, pin);
> +       else if (ops->request)
> +               status = ops->request(pctldev, pin);
> +       else
> +               status = 0;
> +
> +       if (status) {
> +               dev_err(&pctldev->dev, "->request on device %s failed "
> +                      "for pin %d\n",
> +                      pctldev->desc->name, pin);
> +               goto out;
> +       }
> +

... this:

> +       spin_lock(&desc->lock);
> +       desc->mux_requested = true;
> +       strncpy(desc->mux_function, function, sizeof(desc->mux_function));
> +       spin_unlock(&desc->lock);
> +

2 threads can pass through when mux_requested is false and they might
both acquire
the pin, depending on specific driver implementation.

Regards,
Stijn
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