drivers/rtc/rtc-snvs: add clock support

Add clock enable and disable support for the SNVS peripheral, which is
required for using the RTC within the SNVS block.

The clock is not strictly enforced, as this would break the i.MX devices.
The clocking for the i.MX devices seems to be enabled elsewhere and
enabling RTC SNVS for Vybrid results in a crash.  This patch adds the
clock support but also makes it optional so Vybrid platform can use the
clock if defined while making sure not to break i.MX.

Signed-off-by: Sanchayan Maity <maitysanchayan@gmail.com>
Cc: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Stefan Agner <stefan@agner.ch>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-snvs.c

@@ -17,6 +17,7 @@
 #include <linux/of_device.h>
 #include <linux/platform_device.h>
 #include <linux/rtc.h>
+#include <linux/clk.h>
 
 /* These register offsets are relative to LP (Low Power) range */
 #define SNVS_LPCR		0x04
@@ -39,6 +40,7 @@ struct snvs_rtc_data {
 	void __iomem *ioaddr;
 	int irq;
 	spinlock_t lock;
+	struct clk *clk;
 };
 
 static u32 rtc_read_lp_counter(void __iomem *ioaddr)
@@ -260,6 +262,18 @@ static int snvs_rtc_probe(struct platform_device *pdev)
 	if (data->irq < 0)
 		return data->irq;
 
+	data->clk = devm_clk_get(&pdev->dev, "snvs-rtc");
+	if (IS_ERR(data->clk)) {
+		data->clk = NULL;
+	} else {
+		ret = clk_prepare_enable(data->clk);
+		if (ret) {
+			dev_err(&pdev->dev,
+				"Could not prepare or enable the snvs clock\n");
+			return ret;
+		}
+	}
+
 	platform_set_drvdata(pdev, data);
 
 	spin_lock_init(&data->lock);
@@ -280,7 +294,7 @@ static int snvs_rtc_probe(struct platform_device *pdev)
 	if (ret) {
 		dev_err(&pdev->dev, "failed to request irq %d: %d\n",
 			data->irq, ret);
-		return ret;
+		goto error_rtc_device_register;
 	}
 
 	data->rtc = devm_rtc_device_register(&pdev->dev, pdev->name,
@@ -288,10 +302,16 @@ static int snvs_rtc_probe(struct platform_device *pdev)
 	if (IS_ERR(data->rtc)) {
 		ret = PTR_ERR(data->rtc);
 		dev_err(&pdev->dev, "failed to register rtc: %d\n", ret);
-		return ret;
+		goto error_rtc_device_register;
 	}
 
 	return 0;
+
+error_rtc_device_register:
+	if (data->clk)
+		clk_disable_unprepare(data->clk);
+
+	return ret;
 }
 
 #ifdef CONFIG_PM_SLEEP
@@ -302,16 +322,26 @@ static int snvs_rtc_suspend(struct device *dev)
 	if (device_may_wakeup(dev))
 		enable_irq_wake(data->irq);
 
+	if (data->clk)
+		clk_disable_unprepare(data->clk);
+
 	return 0;
 }
 
 static int snvs_rtc_resume(struct device *dev)
 {
 	struct snvs_rtc_data *data = dev_get_drvdata(dev);
+	int ret;
 
 	if (device_may_wakeup(dev))
 		disable_irq_wake(data->irq);
 
+	if (data->clk) {
+		ret = clk_prepare_enable(data->clk);
+		if (ret)
+			return ret;
+	}
+
 	return 0;
 }
 #endif