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