linux-kernel - [PATCH] driver core: Call pm_runtime_put_sync() only after device

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Message-Id: <20230511073428.10264-1-u.kleine-koenig@pengutronix.de>
Date:   Thu, 11 May 2023 09:34:28 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     linux-kernel@...r.kernel.org, kernel@...gutronix.de
Subject: [PATCH] driver core: Call pm_runtime_put_sync() only after device_remove()

Many drivers that use runtime PM call pm_runtime_get_sync() or one of
its variants in their remove callback. So calling pm_runtime_put_sync()
directly before calling the remove callback results (under some
conditions) in the driver's suspend routine being called just to resume
it again afterwards.

So delay the pm_runtime_put_sync() call until after device_remove().

Confirmed on a stm32mp157a that doing

	echo 4400e000.can > /sys/bus/platform/drivers/m_can_platform/unbind

(starting with a runtime-pm suspended 4400e000.can) results in one call
less of m_can_runtime_resume() and m_can_runtime_suspend() each after
this change was applied.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
---
Hello,

side note: To test I added a dev_info() to m_can_runtime_resume() and
m_can_runtime_suspend(). I was surprised that directly after boot I had:

	# dmesg | grep -E '4400e000.can: m_can_runtime_(resume|suspend)' | wc -l
	15

I didn't go down that rabbit hole to debug this.

Best regards
Uwe

 drivers/base/dd.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 9c09ca5c4ab6..d97f6b1486d1 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -1267,10 +1267,10 @@ static void __device_release_driver(struct device *dev, struct device *parent)

 		bus_notify(dev, BUS_NOTIFY_UNBIND_DRIVER);

-		pm_runtime_put_sync(dev);
-
 		device_remove(dev);

+		pm_runtime_put_sync(dev);
+
 		if (dev->bus && dev->bus->dma_cleanup)
 			dev->bus->dma_cleanup(dev);

-- 
2.39.2