coresight: tpiu: retrieve and handle atclk

As can be seen from the datasheet of the CoreSight
Components, DDI0314H page A-19 the TPIU 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 in conjunction.

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-tpiu.c

@@ -20,6 +20,7 @@
 #include <linux/pm_runtime.h>
 #include <linux/coresight.h>
 #include <linux/amba/bus.h>
+#include <linux/clk.h>
 
 #include "coresight-priv.h"
 
@@ -50,11 +51,13 @@
 /**
  * @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 TPIU.
  * @csdev:	component vitals needed by the framework.
  */
 struct tpiu_drvdata {
 	void __iomem		*base;
 	struct device		*dev;
+	struct clk		*atclk;
 	struct coresight_device	*csdev;
 };
 
@@ -111,6 +114,7 @@ static const struct coresight_ops tpiu_cs_ops = {
 
 static int tpiu_probe(struct amba_device *adev, const struct amba_id *id)
 {
+	int ret;
 	void __iomem *base;
 	struct device *dev = &adev->dev;
 	struct coresight_platform_data *pdata = NULL;
@@ -131,6 +135,12 @@ static int tpiu_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 */
@@ -170,6 +180,32 @@ static int tpiu_remove(struct amba_device *adev)
 	return 0;
 }
 
+#ifdef CONFIG_PM
+static int tpiu_runtime_suspend(struct device *dev)
+{
+	struct tpiu_drvdata *drvdata = dev_get_drvdata(dev);
+
+	if (drvdata && !IS_ERR(drvdata->atclk))
+		clk_disable_unprepare(drvdata->atclk);
+
+	return 0;
+}
+
+static int tpiu_runtime_resume(struct device *dev)
+{
+	struct tpiu_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 tpiu_dev_pm_ops = {
+	SET_RUNTIME_PM_OPS(tpiu_runtime_suspend, tpiu_runtime_resume, NULL)
+};
+
 static struct amba_id tpiu_ids[] = {
 	{
 		.id	= 0x0003b912,
@@ -186,6 +222,7 @@ static struct amba_driver tpiu_driver = {
 	.drv = {
 		.name	= "coresight-tpiu",
 		.owner	= THIS_MODULE,
+		.pm	= &tpiu_dev_pm_ops,
 	},
 	.probe		= tpiu_probe,
 	.remove		= tpiu_remove,