On Feb 10, 2010, at 1:20 PM, Grant Likely wrote: > On Wed, Feb 10, 2010 at 11:40 AM, Fleming Andy-AFLEMING > <[email protected]> wrote: >> >> >> On Feb 10, 2010, at 12:15, "Grant Likely" <[email protected]> wrote: >> >>> On Wed, Feb 10, 2010 at 9:52 AM, John Linn <[email protected]> wrote: >>>>> >>>>> -----Original Message----- >>>>> From: [email protected] [mailto:[email protected]] On Behalf Of >>>>> Grant Likely >>>>> Sent: Wednesday, February 10, 2010 9:44 AM >>>>> To: John Linn; devicetree-discuss; netdev >>>>> Subject: Re: phy address in the device tree, vs auto probing >>>>> >>>>> (cc'ing devicetree-discuss and netdev mailing lists) >>>>> >>>>> On Tue, Feb 9, 2010 at 4:23 PM, John Linn <[email protected]> wrote: >>>>>> >>>>>> Hi Grant, >>>>>> >>>>>> I notice that the OF driver for the mdio bus is not doing auto probing. >>>>>> >>>>>> As we start putting in the phy layer in the emac drivers, the device >>>>>> trees tend to have the phy address in them, but we're not sure we >>>>>> really >>>>>> like that. >>>>>> >>>>>> We really think that being able to let the kernel find the phy address >>>>>> is a big benefit, otherwise this is one other piece of info the user >>>>>> has >>>>>> to know and get right. >>>>>> >>>>>> Am I missing something here? >>>>> >>>>> No, you're not really missing something, but there is an inherent >>>>> complexity in what you're wanting to do. Like i2c, MDIO is one of >>>>> those busses that is hard to probe reliable. Some PHYs respond on >>>>> more than one address, and there is no way to determine which MAC a >>>>> PHY is wired up to. Many PHYs can live on a single MDIO bus. MACs >>>>> with their own MDIO busses may still get wired to a PHY on a different >>>>> bus. >>>>> >>>>> In the simple case where there is a one:one:one relationship between >>>>> MAC, MDIO bus and PHY, then it should be okay to probe the PHY, >>>>> correct? The question then must be asked; how does the kernel >>>>> determine that it can use the simple case? Nobody has yet defined a >>>>> way to describe that in the device tree; mostly because nobody has >>>>> needed to yet. >>>>> >>>>> So, it is possible to do what you want, but you need a way to >>>>> *explicitly* ask for that behaviour. ie, some way to indicate in a >>>>> MAC node which MDIO bus the phy is on, and that the phy needs to be >>>>> probed for. I think this should only be an option when the MDIO bus >>>>> has only one PHY. Come up with a proposal and post it to the >>>>> devicetree-discuss mailing list. >>>> >>>> Here's a couple ideas. See what everyone thinks as I'm not stuck on >>>> either. >>>> >>>> Thanks, >>>> John >>>> >>>> 1. What if we just don't specific a phy address with a reg property which >>>> would specify to auto probe it and find the phy as illustrated below? >>>> >>>> >>>> Ethernet_MAC: ether...@81000000 { >>>> #address-cells = <1>; >>>> #size-cells = <1>; >>>> phy-handle = <&phy0>; >>>> mdio { >>>> #address-cells = <1>; >>>> #size-cells = <0>; >>>> phy0: p...@7 { >>>> } ; >>>> } ; >>>> >>>> 2. Or a special value (-1 or something not 0 - 31) in the phy address >>>> that specifies to auto probe as illustrated below. >>>> phy0: p...@7 { >>>> reg = <-1>; >>>> } ; >>> >>> I don't like abusing the reg property in this way. I wonder if a new >>> empty property would be a better way to indicate this. Maybe >>> "phy-probe-address;"? It would also be important to specify in the >>> binding that only one phy node is allowed when phy-probe-address is >>> used. >> >> I don't think it's necessary that only one phy node is there. I don't think >> the of mdio layer should set policy, here. Some drivers hard code their >> addresses. Some drivers assume (foolishly, I think) that the PHYs are in >> order. Many assume there's only one PHY. I think the mdio driver should >> set policy, so of_mdio should just allow for PHYs to be probed. I'm >> actually not sure that requires any changes. Quite possibly this just means >> that of_mdio is not appropriate for such a driver. The standard PHY code >> supports this sort of thing. > > That still doesn't solve the problem of matching PHYs to MACs. > > Consider this example: 2 MACs, 2 PHYs. mac_a--> phy_a and mac_b --> > phy_b. Both phys on the same mdio bus, described thus: > > eth_a: ether...@81000000 { > #address-cells = <1>; > #size-cells = <1>; > phy-handle = <&phy_a>; > mdio { > #address-cells = <1>; > #size-cells = <0>; > phy_a: phy_a { > } ; > phy_b: phy_b { > } ; > } ; > } ; > eth_b: ether...@82000000 { > #address-cells = <1>; > #size-cells = <1>; > phy-handle = <&phy_b>; > } ; > > In this example, the kernel knows it has two phys, and probing > confirms this (say at phy addresses 3 and 7). How does the kernel > know which address phy_a responds to?
There's no way to know. That's what I'm saying. We shouldn't modify the of_mdio code to say which PHY is which. Instead, we have the MDIO/ethernet code do that. And maybe this means that they can't use of_mdio. Or maybe we need to devise a scheme so you can specify those PHYs, but delay associating them with an address until later. Andy _______________________________________________ devicetree-discuss mailing list [email protected] https://lists.ozlabs.org/listinfo/devicetree-discuss
