avr32: Provide a way to deselect pins in the portmux

Currently, setting up the portmux is completely one-shot: Once a pin is
muxed, the portmux driver will complain loudly and refuse to do anything
if you try to set up the same pin again.

Sometimes, it may be necessary to change the configuration of a pin
after it has been set up initially. This patch adds a way to undo the
previous configuration, allowing the pin to be reconfigured.
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>

arch/avr32/mach-at32ap/include/mach/portmux.h

@@ -24,6 +24,7 @@
 void at32_select_periph(unsigned int pin, unsigned int periph,
 			unsigned long flags);
 void at32_select_gpio(unsigned int pin, unsigned long flags);
+void at32_deselect_pin(unsigned int pin);
 void at32_reserve_pin(unsigned int pin);
 
 #endif /* __ASM_ARCH_PORTMUX_H__ */

arch/avr32/mach-at32ap/pio.c

@@ -134,6 +134,25 @@ void __init at32_select_gpio(unsigned int pin, unsigned long flags)
 	dump_stack();
 }
 
+/*
+ * Undo a previous pin reservation. Will not affect the hardware
+ * configuration.
+ */
+void at32_deselect_pin(unsigned int pin)
+{
+	struct pio_device *pio;
+	unsigned int pin_index = pin & 0x1f;
+
+	pio = gpio_to_pio(pin);
+	if (unlikely(!pio)) {
+		printk("pio: invalid pin %u\n", pin);
+		dump_stack();
+		return;
+	}
+
+	clear_bit(pin_index, &pio->pinmux_mask);
+}
+
 /* Reserve a pin, preventing anyone else from changing its configuration. */
 void __init at32_reserve_pin(unsigned int pin)
 {