linux-kernel - Re: [PATCH net v2 2/2] net: usb: asix: ax88772: Increase phy

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Message-ID: <Z9sOmllizdg79UvL@surfacebook.localdomain>
Date: Wed, 19 Mar 2025 20:36:10 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	linux-usb@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, 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>,
	Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [PATCH net v2 2/2] net: usb: asix: ax88772: Increase phy_name
 size

Wed, Mar 19, 2025 at 05:13:52PM +0000, Russell King (Oracle) kirjoitti:
> On Wed, Mar 19, 2025 at 06:22:54PM +0200, Andy Shevchenko wrote:
> > On Wed, Mar 19, 2025 at 02:43:40PM +0000, Russell King (Oracle) wrote:
> > > On Wed, Mar 19, 2025 at 12:54:34PM +0200, Andy Shevchenko wrote:
> > > > -	char phy_name[20];
> > > > +	char phy_name[MII_BUS_ID_SIZE + 3];
> > > 
> > > MII_BUS_ID_SIZE is sized to 61, and is what is used in struct
> > > mii_bus::id. Why there a +3 here, which seems like a random constant to
> > > make it 64-bit aligned in size. If we have need to increase
> > > MII_BUS_ID_SIZE in the future, this kind of alignment then goes
> > > wrong...
> > > 
> > > If the intention is to align it to 64-bit then there's surely a better
> > > and future-proof ways to do that.
> > 
> > Nope, intention is to cover the rest after %s.
> 
> Oops, I had missed that MII_BUS_ID_SIZE is the size of the "%s" part.
> I think linux/phy.h should declare:
> 
> #define PHY_ID_SIZE (MII_BUS_ID_SIZE + 3)
> 
> to cater for the ":XX" that PHY_ID_FMT adds.
> 
> So the above would become:
> 
> 	char phy_name[PHY_ID_SIZE];
> 
> I wonder whether keeping PHY_ID_FMT as-is, but casting the argument
> to a u8 would solve the issue?
> 
> Maybe something like:
> 
> static inline void
> phy_format_id(char *dst, size_t n, const char *mii_bus_id, u8 phy_dev_id)
> {
> 	BUILD_BUG_ON_MSG(n < PHY_ID_SIZE, "PHY ID destination too small");
> 	snprintf(dat, n, PHY_ID_FMT, mii_bus_id, phy_dev_id);
> }
> 
> would solve it?

Would you like to send a formal patch? I will base my fix on top of it and test
that in my case.

-- 
With Best Regards,
Andy Shevchenko