netdev - Re: [PATCH net] net: phy: Decrement phy_fixed

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Message-ID: <576DBB1F.1030208@gmail.com>
Date:	Fri, 24 Jun 2016 15:58:39 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	Russell King - ARM Linux <linux@...linux.org.uk>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, andrew@...n.ch,
	thomas.petazzoni@...e-electrons.com
Subject: 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:
>> 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