On 06/24/2016 04:06 PM, Russell King - ARM Linux wrote: > On Fri, Jun 24, 2016 at 03:58:39PM -0700, Florian Fainelli wrote: >> 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)? > > I would expect an IDA to be suitable, because the IDA would track which > indexes (==addresses) are currently in-use.
OK, thanks! > > If you want to go further, using an IDR would allow fixed_mdio_read() to > find the right fixed_phy struct without needing to loop over fmb->phys. Since I am targetting this as a bugfix, the switch to IDA seems more appropriate to be backported, but yes, that's a good idea though. > Whether that's worth it or not depends if you have a large number of > fixed phys. I suspect we're talking about small quantities here though. > Yes, at the moment we are limited to 32 PHYs maximum, just like a real MDIO bus, which in some systems could actually be not enough, but then you run into other problems, like the need to register more than a single fixed MDIO bus driver to get a larger address space... -- Florian
