Re: [PATCH net-next v2 13/18] net: macb: avoid double endianness swap in macb_set_hwaddr()

From: Sean Anderson <sean.anderson@linux.dev>
To: "Théo Lebrun" <theo.lebrun@bootlin.com>,
	"Andrew Lunn" <andrew+netdev@lunn.ch>,
	"David S. Miller" <davem@davemloft.net>,
	"Eric Dumazet" <edumazet@google.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Paolo Abeni" <pabeni@redhat.com>,
	"Rob Herring" <robh@kernel.org>,
	"Krzysztof Kozlowski" <krzk+dt@kernel.org>,
	"Conor Dooley" <conor+dt@kernel.org>,
	"Nicolas Ferre" <nicolas.ferre@microchip.com>,
	"Claudiu Beznea" <claudiu.beznea@tuxon.dev>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Alexandre Ghiti" <alex@ghiti.fr>,
	"Samuel Holland" <samuel.holland@sifive.com>,
	"Richard Cochran" <richardcochran@gmail.com>,
	"Russell King" <linux@armlinux.org.uk>,
	"Thomas Bogendoerfer" <tsbogend@alpha.franken.de>,
	"Vladimir Kondratiev" <vladimir.kondratiev@mobileye.com>,
	"Gregory CLEMENT" <gregory.clement@bootlin.com>,
	"Cyrille Pitchen" <cyrille.pitchen@atmel.com>,
	"Harini Katakam" <harini.katakam@xilinx.com>,
	"Rafal Ozieblo" <rafalo@cadence.com>,
	"Haavard Skinnemoen" <hskinnemoen@atmel.com>,
	"Jeff Garzik" <jeff@garzik.org>
Cc: netdev@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
	linux-mips@vger.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Tawfik Bayouk <tawfik.bayouk@mobileye.com>
Subject: Re: [PATCH net-next v2 13/18] net: macb: avoid double endianness swap in macb_set_hwaddr()
Date: Tue, 1 Jul 2025 12:44:55 -0400	[thread overview]
Message-ID: <34647b2e-3d9d-42db-9851-34ad8621af02@linux.dev> (raw)
In-Reply-To: <20250627-macb-v2-13-ff8207d0bb77@bootlin.com>

On 6/27/25 05:08, Théo Lebrun wrote:
> 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")
> Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.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 578e72c7727d4f578478ff2b3d0a6316327271b1..34223dad2d01ae4bcefc0823c868a67f59435638 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -265,9 +265,9 @@ 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)) {
> 

Reviewed-by: Sean Anderson <sean.anderson@linux.dev>