gpio: mvebu: Add clk support to prevent lockup

The kirkwood SoC GPIO cores use the runit clock. Add code to
clk_prepare_enable() runit, otherwise there is a danger of locking up
the SoC by accessing the GPIO registers when runit clock is not
ticking.
Reported-by: NSimon Baatz <gmbnomis@gmail.com>
Signed-off-by: NAndrew Lunn <andrew@lunn.ch>
Tested-by: NSimon Baatz <gmbnomis@gmail.com>
Acked-by: NLinus Walleij <linus.walleij@linaro.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: NJason Cooper <jason@lakedaemon.net>

arch/arm/boot/dts/kirkwood.dtsi

@@ -38,6 +38,7 @@
 			interrupt-controller;
 			#interrupt-cells = <2>;
 			interrupts = <35>, <36>, <37>, <38>;
+			clocks = <&gate_clk 7>;
 		};
 
 		gpio1: gpio@10140 {
@@ -49,6 +50,7 @@
 			interrupt-controller;
 			#interrupt-cells = <2>;
 			interrupts = <39>, <40>, <41>;
+			clocks = <&gate_clk 7>;
 		};
 
 		serial@12000 {

drivers/gpio/gpio-mvebu.c

@@ -42,6 +42,7 @@
 #include <linux/io.h>
 #include <linux/of_irq.h>
 #include <linux/of_device.h>
+#include <linux/clk.h>
 #include <linux/pinctrl/consumer.h>
 
 /*
@@ -496,6 +497,7 @@ static int mvebu_gpio_probe(struct platform_device *pdev)
 	struct resource *res;
 	struct irq_chip_generic *gc;
 	struct irq_chip_type *ct;
+	struct clk *clk;
 	unsigned int ngpios;
 	int soc_variant;
 	int i, cpu, id;
@@ -529,6 +531,11 @@ static int mvebu_gpio_probe(struct platform_device *pdev)
 		return id;
 	}
 
+	clk = devm_clk_get(&pdev->dev, NULL);
+	/* Not all SoCs require a clock.*/
+	if (!IS_ERR(clk))
+		clk_prepare_enable(clk);
+
 	mvchip->soc_variant = soc_variant;
 	mvchip->chip.label = dev_name(&pdev->dev);
 	mvchip->chip.dev = &pdev->dev;