netdev - [PATCH net v4 5/5] net: macb: avoid double endianness swap in macb_set

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Message-Id: <20250820-macb-fixes-v4-5-23c399429164@bootlin.com>
Date: Wed, 20 Aug 2025 16:55:09 +0200
From: Théo Lebrun <theo.lebrun@...tlin.com>
To: Andrew Lunn <andrew+netdev@...n.ch>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, 
 Nicolas Ferre <nicolas.ferre@...rochip.com>, 
 Claudiu Beznea <claudiu.beznea@...on.dev>, 
 Geert Uytterhoeven <geert@...ux-m68k.org>, 
 Harini Katakam <harini.katakam@...inx.com>, 
 Richard Cochran <richardcochran@...il.com>, 
 Russell King <linux@...linux.org.uk>
Cc: netdev@...r.kernel.org, devicetree@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 Tawfik Bayouk <tawfik.bayouk@...ileye.com>, 
 Théo Lebrun <theo.lebrun@...tlin.com>, 
 Sean Anderson <sean.anderson@...ux.dev>
Subject: [PATCH net v4 5/5] net: macb: avoid double endianness swap in
 macb_set_hwaddr()

writel() does a CPU->LE conversion. Drop manual cpu_to_le*() calls.

On little-endian system:
 - cpu_to_le32() is a no-op (LE->LE),
 - writel() is a no-op (LE->LE),
 - dev_addr will therefore not be swapped and written as-is.

On big-endian system:
 - cpu_to_le32() is a swap (BE->LE),
 - writel() is a swap (BE->LE),
 - dev_addr will therefore be swapped twice and written as a BE value.

This was found using sparse:
   ⟩ make C=2 drivers/net/ethernet/cadence/macb_main.o
   warning: incorrect type in assignment (different base types)
      expected unsigned int [usertype] bottom
      got restricted __le32 [usertype]
   warning: incorrect type in assignment (different base types)
      expected unsigned short [usertype] top
      got restricted __le16 [usertype]
   ...

Fixes: 89e5785fc8a6 ("[PATCH] Atmel MACB ethernet driver")
Reviewed-by: Sean Anderson <sean.anderson@...ux.dev>
Signed-off-by: Théo Lebrun <theo.lebrun@...tlin.com>
---
 drivers/net/ethernet/cadence/macb_main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index 7f31f264a6d342ea01e2f61944b12c9b9a3fe66e..fe319d77f2a8f6b1f3b698e0d11781936345ea8f 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -274,9 +274,9 @@ static void macb_set_hwaddr(struct macb *bp)
 	u32 bottom;
 	u16 top;

-	bottom = cpu_to_le32(*((u32 *)bp->dev->dev_addr));
+	bottom = *((u32 *)bp->dev->dev_addr);
 	macb_or_gem_writel(bp, SA1B, bottom);
-	top = cpu_to_le16(*((u16 *)(bp->dev->dev_addr + 4)));
+	top = *((u16 *)(bp->dev->dev_addr + 4));
 	macb_or_gem_writel(bp, SA1T, top);

 	if (gem_has_ptp(bp)) {

-- 
2.50.1