gpio: mxc: add clock operation

Some i.MX SoCs have GPIO clock gates in CCM CCGR, such as
i.MX6SLL, need to enable clocks before accessing GPIO
registers, add optional clock operation for GPIO driver.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-mxc.c

@@ -20,6 +20,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  */
 
+#include <linux/clk.h>
 #include <linux/err.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
@@ -60,6 +61,7 @@ struct mxc_gpio_hwdata {
 struct mxc_gpio_port {
 	struct list_head node;
 	void __iomem *base;
+	struct clk *clk;
 	int irq;
 	int irq_high;
 	struct irq_domain *domain;
@@ -434,6 +436,17 @@ static int mxc_gpio_probe(struct platform_device *pdev)
 	if (port->irq < 0)
 		return port->irq;
 
+	/* the controller clock is optional */
+	port->clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(port->clk))
+		port->clk = NULL;
+
+	err = clk_prepare_enable(port->clk);
+	if (err) {
+		dev_err(&pdev->dev, "Unable to enable clock.\n");
+		return err;
+	}
+
 	/* disable the interrupt and clear the status */
 	writel(0, port->base + GPIO_IMR);
 	writel(~0, port->base + GPIO_ISR);
@@ -502,6 +515,7 @@ static int mxc_gpio_probe(struct platform_device *pdev)
 out_irqdomain_remove:
 	irq_domain_remove(port->domain);
 out_bgio:
+	clk_disable_unprepare(port->clk);
 	dev_info(&pdev->dev, "%s failed with errno %d\n", __func__, err);
 	return err;
 }