Re: [PATCH net] net: phy: Decrement phy_fixed_addr during unregister

On 06/24/2016 03:55 PM, Russell King - ARM Linux wrote:

On Fri, Jun 24, 2016 at 03:44:11PM -0700, Florian Fainelli wrote:

quoted

If we have a system which uses fixed PHY devices and calls
fixed_phy_register() then fixed_phy_unregister() we can exhaust the
number of fixed PHYs available after a while, since we keep incrementing
the variable phy_fixed_addr, but we never decrement it.

This patch fixes that by decrementing phy_fixed_addr during
fixed_phy_del(), and in order to do that, we need to move the
phy_fixed_addr integer and its spinlock above that function.

Is this really a good idea?

In the sense that it is symetrical to the register code, probably.

What if we have two fixed phys register, and the first one is
unregistered and a new one subsequently registered?

First phy registered, gets address 0, phy_fixed_addr becomes 1.
Second phy registered, gets address 1, phy_fixed_addr becomes 2.
First phy is unregistered, phy_fixed_addr becomes 1.
Third phy registered, gets address 1, conflicts with the second phy.

Obviously not a good outcome.

What would you suggest we do instead? Would switching to IDA/IDR give us
better results for instance (I have not looked too closely yet)?
-- 
Florian