coresight: etm: retrieve and handle atclk

As can be seen from the datasheet of the CoreSight
Components, DDI0401C A.1.1 the ETM 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-etm.h

@@ -140,6 +140,7 @@
  * struct etm_drvdata - specifics associated to an ETM 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 ETM.
  * @csdev:	component vitals needed by the framework.
  * @spinlock:	only one at a time pls.
  * @cpu:	the cpu this component is affined to.
@@ -191,6 +192,7 @@
 struct etm_drvdata {
 	void __iomem			*base;
 	struct device			*dev;
+	struct clk			*atclk;
 	struct coresight_device		*csdev;
 	spinlock_t			spinlock;
 	int				cpu;

drivers/hwtracing/coresight/coresight-etm3x.c

@@ -30,6 +30,7 @@
 #include <linux/amba/bus.h>
 #include <linux/seq_file.h>
 #include <linux/uaccess.h>
+#include <linux/clk.h>
 #include <asm/sections.h>
 
 #include "coresight-etm.h"
@@ -1315,7 +1316,6 @@ static ssize_t seq_curr_state_show(struct device *dev,
 	}
 
 	pm_runtime_get_sync(drvdata->dev);
-
 	spin_lock_irqsave(&drvdata->spinlock, flags);
 
 	CS_UNLOCK(drvdata->base);
@@ -1796,6 +1796,13 @@ static int etm_probe(struct amba_device *adev, const struct amba_id *id)
 
 	spin_lock_init(&drvdata->spinlock);
 
+	drvdata->atclk = devm_clk_get(&adev->dev, "atclk"); /* optional */
+	if (!IS_ERR(drvdata->atclk)) {
+		ret = clk_prepare_enable(drvdata->atclk);
+		if (ret)
+			return ret;
+	}
+
 	drvdata->cpu = pdata ? pdata->cpu : 0;
 
 	get_online_cpus();
@@ -1858,6 +1865,32 @@ static int etm_remove(struct amba_device *adev)
 	return 0;
 }
 
+#ifdef CONFIG_PM
+static int etm_runtime_suspend(struct device *dev)
+{
+	struct etm_drvdata *drvdata = dev_get_drvdata(dev);
+
+	if (drvdata && !IS_ERR(drvdata->atclk))
+		clk_disable_unprepare(drvdata->atclk);
+
+	return 0;
+}
+
+static int etm_runtime_resume(struct device *dev)
+{
+	struct etm_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 etm_dev_pm_ops = {
+	SET_RUNTIME_PM_OPS(etm_runtime_suspend, etm_runtime_resume, NULL)
+};
+
 static struct amba_id etm_ids[] = {
 	{	/* ETM 3.3 */
 		.id	= 0x0003b921,
@@ -1886,6 +1919,7 @@ static struct amba_driver etm_driver = {
 	.drv = {
 		.name	= "coresight-etm3x",
 		.owner	= THIS_MODULE,
+		.pm	= &etm_dev_pm_ops,
 	},
 	.probe		= etm_probe,
 	.remove		= etm_remove,