[AVR32] Introduce at32_reserve_pin()

at32_reserve_pin() can be used for reserving portmux pins without
altering their configuration. Useful for e.g. SDRAM pins where we
really don't want to change the bootloader-provided configuration.
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>

arch/avr32/mach-at32ap/pio.c

@@ -135,7 +135,28 @@ void __init at32_select_gpio(unsigned int pin, unsigned long flags)
 	dump_stack();
 }
 
-/*--------------------------------------------------------------------------*/
+/* Reserve a pin, preventing anyone else from changing its configuration. */
+void __init at32_reserve_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);
+		goto fail;
+	}
+
+	if (unlikely(test_and_set_bit(pin_index, &pio->pinmux_mask))) {
+		printk("%s: pin %u is busy\n", pio->name, pin_index);
+		goto fail;
+	}
+
+	return;
+
+fail:
+	dump_stack();
+}
 
 /*--------------------------------------------------------------------------*/
 

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

@@ -23,5 +23,6 @@
 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_reserve_pin(unsigned int pin);
 
 #endif /* __ASM_ARCH_PORTMUX_H__ */