Re: [net-next PATCH v7 2/4] net: phy: extend PHY package API to support multiple global address

["Russell King (Oracle)" <linux@armlinux.org.uk>]

On Thu, Dec 14, 2023 at 01:10:24PM +0100, Christian Marangi wrote:
> @@ -1998,46 +1999,54 @@ int __phy_hwtstamp_set(struct phy_device *phydev,
>  		       struct kernel_hwtstamp_config *config,
>  		       struct netlink_ext_ack *extack);
>  
> -static inline int phy_package_read(struct phy_device *phydev, u32 regnum)
> +static inline int phy_package_read(struct phy_device *phydev,
> +				   unsigned int addr_offset, u32 regnum)
>  {
>  	struct phy_package_shared *shared = phydev->shared;
> +	u8 addr = shared->base_addr + addr_offset;
>  
> -	if (!shared)
> +	if (addr >= PHY_MAX_ADDR)
>  		return -EIO;

I did notice that you're using u8 in patch 1 as well - and while it's
fine in patch 1 (because we validate the range of the value we will
assign to that variable) that is not the case here.

Yes, shared->base_addr is a u8, but addr_offset is an unsigned int,
and this is implicitly cast-down to a u8 in the calculation of addr,
chopping off the bits above bit 7.

How about this approach:

static int phy_package_address(struct phy_device *phydev,
			       unsigned int addr_offset)
{
	struct phy_package_shared *shared = phydev->shared;
	unsigned int addr = shared->addr + addr_offset;

	/* detect wrap */
	if (addr < addr_offset)
		return -EIO;

	/* detect invalid address */
	if (addr >= PHY_ADDR_MAX)
		return -EIO;

	/* we know that addr will be in the range 0..31 and thus the
	 * implicit cast to a signed int is not a problem.
	 */
	return addr;
}

and then these functions all become:

	int addr = phy_package_address(phydev, addr_offset);

	if (addr < 0)
		return addr;

I'll give you that this is belt and braces, but it avoids problems
should a negative errno value be passed in as addr_offset (which will
be cast to a very large positive integer.)

Andrew, any opinions on how far this should be taken?

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