coresight: etb: retrieve and handle atclk

As can be seen from the datasheet of the CoreSight
Components, DDI0314 table A-8 the ETB has a clock signal
apart from the AHB interconnect ("amba_pclk", that we're
already handling) called ATCLK, ARM Trace Clock, that SoC
implementers may provide from an entirely different clock
source. So to model this correctly create an optional
path for handling ATCLK alongside the PCLK so we don't
break old platforms that only define PCLK ("amba_pclk") but
still makes it possible for SoCs that have both clock signals
(such as the DB8500) to fetch and prepare/enable/disable/
unprepare both clocks.

The ATCLK is enabled and disabled using the runtime PM
callbacks.

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight-etb10.c

@@ -26,6 +26,7 @@
 #include <linux/seq_file.h>
 #include <linux/coresight.h>
 #include <linux/amba/bus.h>
+#include <linux/clk.h>
 
 #include "coresight-priv.h"
 
@@ -66,6 +67,7 @@
  * struct etb_drvdata - specifics associated to an ETB component
  * @base:	memory mapped base address for this component.
  * @dev:	the device entity associated to this component.
+ * @atclk:	optional clock for the core parts of the ETB.
  * @csdev:	component vitals needed by the framework.
  * @miscdev:	specifics to handle "/dev/xyz.etb" entry.
  * @spinlock:	only one at a time pls.
@@ -78,6 +80,7 @@
 struct etb_drvdata {
 	void __iomem		*base;
 	struct device		*dev;
+	struct clk		*atclk;
 	struct coresight_device	*csdev;
 	struct miscdevice	miscdev;
 	spinlock_t		spinlock;
@@ -426,6 +429,12 @@ static int etb_probe(struct amba_device *adev, const struct amba_id *id)
 		return -ENOMEM;
 
 	drvdata->dev = &adev->dev;
+	drvdata->atclk = devm_clk_get(&adev->dev, "atclk"); /* optional */
+	if (!IS_ERR(drvdata->atclk)) {
+		ret = clk_prepare_enable(drvdata->atclk);
+		if (ret)
+			return ret;
+	}
 	dev_set_drvdata(dev, drvdata);
 
 	/* validity for the resource is already checked by the AMBA core */
@@ -489,6 +498,32 @@ static int etb_remove(struct amba_device *adev)
 	return 0;
 }
 
+#ifdef CONFIG_PM
+static int etb_runtime_suspend(struct device *dev)
+{
+	struct etb_drvdata *drvdata = dev_get_drvdata(dev);
+
+	if (drvdata && !IS_ERR(drvdata->atclk))
+		clk_disable_unprepare(drvdata->atclk);
+
+	return 0;
+}
+
+static int etb_runtime_resume(struct device *dev)
+{
+	struct etb_drvdata *drvdata = dev_get_drvdata(dev);
+
+	if (drvdata && !IS_ERR(drvdata->atclk))
+		clk_prepare_enable(drvdata->atclk);
+
+	return 0;
+}
+#endif
+
+static const struct dev_pm_ops etb_dev_pm_ops = {
+	SET_RUNTIME_PM_OPS(etb_runtime_suspend, etb_runtime_resume, NULL)
+};
+
 static struct amba_id etb_ids[] = {
 	{
 		.id	= 0x0003b907,
@@ -501,6 +536,8 @@ static struct amba_driver etb_driver = {
 	.drv = {
 		.name	= "coresight-etb10",
 		.owner	= THIS_MODULE,
+		.pm	= &etb_dev_pm_ops,
+
 	},
 	.probe		= etb_probe,
 	.remove		= etb_remove,