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Date: Thu, 14 Dec 2023 23:54:26 +0000
From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Christian Marangi <ansuelsmth@gmail.com>
Cc: Florian Fainelli <florian.fainelli@broadcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@broadcom.com>,
	Andrew Lunn <andrew@lunn.ch>,
	Heiner Kallweit <hkallweit1@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Vladimir Oltean <olteanv@gmail.com>,
	David Epping <david.epping@missinglinkelectronics.com>,
	Harini Katakam <harini.katakam@amd.com>, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [net-next PATCH v7 2/4] net: phy: extend PHY package API to
 support multiple global address
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Sender: Russell King (Oracle) <linux@armlinux.org.uk>

On Thu, Dec 14, 2023 at 05:54:51PM +0100, Christian Marangi wrote:
> What I don't like is the wrap check.
> 
> But I wonder... Isn't it easier to have 
> 
> unsigned int addr = shared->base_addr + addr_offset;
> 
> and check if >= PHY_MAC_ADDR?
> 
> Everything is unsigned (so no negative case) and wrap is not possible as
> nothing is downcasted.

I'm afraid that I LOL'd at "wrap is not possible" ! Of course it's
possible. Here's an example:

	shared->base_addr is 20
	addr_offset is ~0 (or -1 casted to an unsigned int)
	addr becomes 19

How about:

	if (addr_offset >= PHY_MAX_ADDR)
		return -EIO;

	addr = shared->base_addr + addr_offset;
	if (addr >= PHY_MAX_ADDR)
		return -EIO;

and then we could keep 'addr' as u8.

Honestly, I have wondered why the mdio bus address is a signed int, but
never decided to do anything about it.

-- 
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