gpio: gpio-dwapb: add optional reset

Some platforms require reset to be released to allow register
access.

Signed-off-by: Alan Tull <atull@kernel.org>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
[Added DT bindings oneliner for standard reset binding]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/gpio/snps-dwapb-gpio.txt

@@ -29,6 +29,7 @@ controller.
 - interrupts : The interrupt to the parent controller raised when GPIOs
   generate the interrupts.
 - snps,nr-gpios : The number of pins in the port, a single cell.
+- resets : Reset line for the controller.
 
 Example:
 

drivers/gpio/gpio-dwapb.c

@@ -25,6 +25,7 @@
 #include <linux/of_irq.h>
 #include <linux/platform_device.h>
 #include <linux/property.h>
+#include <linux/reset.h>
 #include <linux/spinlock.h>
 #include <linux/platform_data/gpio-dwapb.h>
 #include <linux/slab.h>
@@ -98,6 +99,7 @@ struct dwapb_gpio {
 	unsigned int		nr_ports;
 	struct irq_domain	*domain;
 	unsigned int		flags;
+	struct reset_control	*rst;
 };
 
 static inline u32 gpio_reg_v2_convert(unsigned int offset)
@@ -629,6 +631,12 @@ static int dwapb_gpio_probe(struct platform_device *pdev)
 	gpio->dev = &pdev->dev;
 	gpio->nr_ports = pdata->nports;
 
+	gpio->rst = devm_reset_control_get_optional_shared(dev, NULL);
+	if (IS_ERR(gpio->rst))
+		return PTR_ERR(gpio->rst);
+
+	reset_control_deassert(gpio->rst);
+
 	gpio->ports = devm_kcalloc(&pdev->dev, gpio->nr_ports,
 				   sizeof(*gpio->ports), GFP_KERNEL);
 	if (!gpio->ports)
@@ -680,6 +688,7 @@ static int dwapb_gpio_remove(struct platform_device *pdev)
 
 	dwapb_gpio_unregister(gpio);
 	dwapb_irq_teardown(gpio);
+	reset_control_assert(gpio->rst);
 
 	return 0;
 }