pinctrl: allow exlusive GPIO/mux pin allocation

Disallow simultaneous use of the the GPIO and peripheral mux
functions by setting a flag "strict" in struct pinctrl_desc.

The blackfin pinmux and gpio controller doesn't allow user to
set up a pin for both GPIO and peripheral function. So, add flag
strict in struct pinctrl_desc to check both gpio_owner and
mux_owner before approving the pin request.

v2-changes:
- if strict flag is set, check gpio_owner and mux_onwer in if and
  else clause

v3-changes:
- add kerneldoc for this struct
- augment Documentation/pinctrl.txt

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/pinctrl/pinctrl.h

@@ -114,6 +114,8 @@ struct pinctrl_ops {
  *	of the pins field above
  * @pctlops: pin control operation vtable, to support global concepts like
  *	grouping of pins, this is optional.
+ * @strict: check both gpio_owner and mux_owner strictly before approving
+	the pin request
  * @pmxops: pinmux operations vtable, if you support pinmuxing in your driver
  * @confops: pin config operations vtable, if you support pin configuration in
  *	your driver
@@ -132,6 +134,7 @@ struct pinctrl_desc {
 	const struct pinctrl_ops *pctlops;
 	const struct pinmux_ops *pmxops;
 	const struct pinconf_ops *confops;
+	bool strict;
 	struct module *owner;
 #ifdef CONFIG_GENERIC_PINCONF
 	unsigned int num_custom_params;