netdev - [PATCH net v1 1/1] net: lan78xx: fix runtime PM count underflow on link stop

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Message-Id: <20240228124517.1702476-1-o.rempel@pengutronix.de>
Date: Wed, 28 Feb 2024 13:45:17 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Woojung Huh <woojung.huh@...rochip.com>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>,
	kernel@...gutronix.de,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	UNGLinuxDriver@...rochip.com
Subject: [PATCH net v1 1/1] net: lan78xx: fix runtime PM count underflow on link stop

Current driver has some asymmetry in the runtime PM calls. On lan78xx_open()
it will call usb_autopm_get() and unconditionally usb_autopm_put(). And
on lan78xx_stop() it will call only usb_autopm_put(). So far, it was
working only because this driver do not activate autosuspend by default,
so it was visible only by warning "Runtime PM usage count underflow!".

Since, with current driver, we can't use runtime PM with active link,
execute lan78xx_open()->usb_autopm_put() only in error case. Otherwise,
keep ref counting high as long as interface is open.

Fixes: 55d7de9de6c3 ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 Ethernet device driver")
Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
 drivers/net/usb/lan78xx.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index 3ff430198512..80ee4fcdfb36 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -3135,7 +3135,8 @@ static int lan78xx_open(struct net_device *net)
 done:
 	mutex_unlock(&dev->dev_mutex);

-	usb_autopm_put_interface(dev->intf);
+	if (ret < 0)
+		usb_autopm_put_interface(dev->intf);

 	return ret;
 }
-- 
2.39.2