linux-kernel - [PATCH net-next v1 1/1] net: usb: lan78xx: annotate checksum assignment to silence sparse warnings

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Message-Id: <20250620084618.1857662-1-o.rempel@pengutronix.de>
Date: Fri, 20 Jun 2025 10:46:18 +0200
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>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	Russell King <rmk+kernel@...linux.org.uk>,
	Thangaraj Samynathan <Thangaraj.S@...rochip.com>,
	Rengarajan Sundararajan <Rengarajan.S@...rochip.com>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>,
	kernel@...gutronix.de,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	UNGLinuxDriver@...rochip.com,
	Phil Elwell <phil@...pberrypi.org>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	Simon Horman <horms@...nel.org>
Subject: [PATCH net-next v1 1/1] net: usb: lan78xx: annotate checksum assignment to silence sparse warnings

sparse warns about suspicious type casts in checksum assignment:

drivers/net/usb/lan78xx.c:3865:29: warning: cast to restricted __be16
drivers/net/usb/lan78xx.c:3865:27: warning: incorrect type in assignment
    (different base types) expected restricted __wsum [usertype] csum
got unsigned short [usertype]

Use __force to annotate the casts from u16 to __be16 to __wsum.
This makes the type conversion explicit and silences the warnings.
The code is otherwise correct; this change only clarifies intent.

Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
 drivers/net/usb/lan78xx.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index f00284c9ad34..565b9847e2ab 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -3819,7 +3819,10 @@ static void lan78xx_rx_csum_offload(struct lan78xx_net *dev,
 	     !(dev->net->features & NETIF_F_HW_VLAN_CTAG_RX))) {
 		skb->ip_summed = CHECKSUM_NONE;
 	} else {
-		skb->csum = ntohs((u16)(rx_cmd_b >> RX_CMD_B_CSUM_SHIFT_));
+		__be16 csum_raw;
+
+		csum_raw = (__force __be16)(rx_cmd_b >> RX_CMD_B_CSUM_SHIFT_);
+		skb->csum = (__force __wsum)ntohs(csum_raw);
 		skb->ip_summed = CHECKSUM_COMPLETE;
 	}
 }
-- 
2.39.5