[PATCH v2 2/2] coresight: tnoc: Fix clock refcount imbalance on platform remove

[Jie Gan <jie.gan@oss.qualcomm.com>]

coresight_get_enable_clocks() enables the programming clock through
devm_clk_get_optional_enabled(), which also registers a devm action to
call clk_disable_unprepare() when the driver detaches.

After probe, pm_runtime_put() allows the device to suspend and the
runtime suspend callback disables the clock. During remove the device is
left runtime suspended, so pm_runtime_disable() freezes it with the
clock already disabled. The devm cleanup that runs afterwards calls
clk_disable_unprepare() a second time, underflowing the clock enable
refcount.

Resume the device with pm_runtime_get_sync() before tearing it down so
the clock is enabled again and balances the devm-managed disable. Then
pm_runtime_set_suspended() and pm_runtime_put_noidle() leave the device
in a coherent runtime PM state (suspended, usage count balanced) once
the devm action has disabled the clock.

Fixes: 1abc1b212eff ("coresight: Appropriately disable programming clocks")
Signed-off-by: Jie Gan <jie.gan@oss.qualcomm.com>
---
 drivers/hwtracing/coresight/coresight-tnoc.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/hwtracing/coresight/coresight-tnoc.c b/drivers/hwtracing/coresight/coresight-tnoc.c
index 9e8de4323d28..eddfdcbaa3ec 100644
--- a/drivers/hwtracing/coresight/coresight-tnoc.c
+++ b/drivers/hwtracing/coresight/coresight-tnoc.c
@@ -282,42 +282,50 @@ static int itnoc_probe(struct platform_device *pdev)
 {
 	struct resource *res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	int ret;
 
 	pm_runtime_get_noresume(&pdev->dev);
 	pm_runtime_set_active(&pdev->dev);
 	pm_runtime_enable(&pdev->dev);
 
 	ret = _tnoc_probe(&pdev->dev, res);
 	pm_runtime_put(&pdev->dev);
 	if (ret)
 		pm_runtime_disable(&pdev->dev);
 
 	return ret;
 }
 
 static void itnoc_remove(struct platform_device *pdev)
 {
 	struct trace_noc_drvdata *drvdata = platform_get_drvdata(pdev);
 
+	/*
+	 * Resume the device so its clocks are enabled again, balancing the
+	 * clk_disable_unprepare() that devm runs when the driver detaches.
+	 * Then mark it suspended and drop the usage count taken here.
+	 */
+	pm_runtime_get_sync(&pdev->dev);
 	coresight_unregister(drvdata->csdev);
 	pm_runtime_disable(&pdev->dev);
+	pm_runtime_set_suspended(&pdev->dev);
+	pm_runtime_put_noidle(&pdev->dev);
 }
 
 #ifdef CONFIG_PM
 static int itnoc_runtime_suspend(struct device *dev)
 {
 	struct trace_noc_drvdata *drvdata = dev_get_drvdata(dev);
 
 	clk_disable_unprepare(drvdata->pclk);
 
 	return 0;
 }
 
 static int itnoc_runtime_resume(struct device *dev)
 {
 	struct trace_noc_drvdata *drvdata = dev_get_drvdata(dev);
 
 	return clk_prepare_enable(drvdata->pclk);
 }
 #endif
 

-- 
2.34.1