Re: [PATCH net v2 2/2] net: usb: asix: ax88772: Increase phy_name size

[Russell King (Oracle)]

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?

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