[U-Boot] [PATCH v4 3/3] cmd: mdio: Add new parameter to access MMD PHY registers

[Joe Hershberger]

On Mon, Feb 4, 2019 at 5:39 PM Vladimir Oltean <vladimir.oltean at nxp.com> wrote:
>
> On 2/5/19 1:28 AM, Joe Hershberger wrote:
> > On Fri, Jan 25, 2019 at 7:12 AM Vladimir Oltean <vladimir.oltean at nxp.com> wrote:
> >>
> >> On 25.01.2019 12:12, Carlo Caione wrote:
> >>> On 24/01/2019 20:48, Vladimir Oltean wrote:
> >>>> On 1/24/19 10:19 PM, Carlo Caione wrote:
> >>>>> On 24/01/2019 20:12, Vladimir Oltean wrote:
> >>>>>>
> >>>>
> >>>> I can't completely answer that, TBH I don't even know who is supposed to
> >>>> make that distinction.
> >>>
> >>> In the kernel that distinction is made by the driver itself, hence my
> >>> question. See [0].
> >>>
> >>>> For Freescale parts that is a call for the MDIO bus driver to make, for
> >>>> good or bad (see drivers/net/fm/memac_phy.c where dev_addr is compared
> >>>> to MDIO_DEVAD_NONE).
> >>>
> >>>> And in your patch, phy_write_mmd is only a wrapper over bus->write in
> >>>> the end, with some more logic to handle C22 indirection.
> >>>> So my question of unifying "mdio rmmd" with "mdio read" translates into:
> >>>
> >>>> Does it make sense to also handle the check with MDIO_DEVAD_NONE in
> >>>> phy_write_mmd, instead of jumping straight ahead to perform indirection?
> >>>
> >>> Honestly I'm not quite sure of all the possible implications here IMO
> >>> the safest bet here is just to follow what's done by the kernel. Maybe
> >>> Joe can step in about this.
> >>>
> >>> In general we have 3 possible cases:
> >>>
> >>> 1) your driver is doing something non-standard when accessing the MMDs
> >>> and we deal with that using the PHY driver hooks
> >>> 2) your PHY is C22 and you have to use the indirect method
> >>> 3) your PHY is C45 and you can use the direct register reading (mangling
> >>> a bit the address apparently)
> >>>
> >>> The kernel is dealing with all the cases, U-Boot is only dealing with
> >>> C22 PHYs (cases 1 and 2) because AFAICT there isn't yet a generic way to
> >>> detect if the PHY is C22 or C45.
> >>>
> >>> I'm not sure if the indirect method works also for C45 PHYs.
> >>>
> >>>> The goal would then be to just call phy_write_mmd from cmd/mdio.c
> >>>> regardless of the target PHY's clause.
> >>>
> >>> Again I wrote that patch only assuming that we were going to deal with
> >>> C22 PHYs. At this point I wonder if the C22 indirect method works also
> >>> for C45 PHYs. If that's the case than the phy_write_mmd should already
> >>> work regardless of the target PHY clause.
> >>>
> >>> Cheers.
> >>>
> >>> [0]
> >>> https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Felixir.bootlin.com%2Flinux%2Flatest%2Fsource%2Fdrivers%2Fnet%2Fphy%2Fphy-core.c%23L296&data=02%7C01%7Cvladimir.oltean%40nxp.com%7C826fd741578446f6f36908d68af87b27%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C636849197162094704&sdata=r9AlGZbzGtLC2z7u2HgKKZt17Cl1OcHncjeY00xlVWE%3D&reserved=0
> >>>
> >>
> >> I'm not suggesting to use C22 indirection if the PHY already supports
> >> native C45 addressing. Even if that worked, it would be a pointless
> >> exercise in all but a few cases (like the MDIO controller does not
> >> support C22, but the PHY does support both C22 and C45).
> >> I was just wondering out loud whether the introduction of the "mdio
> >> rmmd" command is justified or not. I now understand that using e.g.
> >> "mdio read 1.3" will confuse the command for clause 45 PHY's because it
> >> won't know whether it should access the PHY via native C45 or via
> >> indirect C22 (obviously it shouldn't do the latter). So in lack of a
> >> clear distinction mechanism, I now think that a new command truly is
> >> necessary for performing indirect C45 access on C22.
> >> What I am still not convinced of, however, is whether those commands
> >> should be called "rmmd" and "wmmd". It is not immediately obvious from
> >> the command description that this is what they are for, and a user may
> >> attempt to use them for C45 PHY's as well, which will probably not yield
> >> the intended result.
> >
> > I agree. The MMD in the register name is simply "MDIO Manageable
> > Devices"... i.e. the phys.
> >
> > I think the commands should be "iread" and "iwrite" to denote the
> > indirect access in use.
> >
>
> Which brings me to my next point.
> If we can't properly make the distinction between an indirect C22 MMD
> access and a proper C45 MMD access, and hence not keeping proper API
> compatibility with Linux kernel, aren't we better off going back to
> square 1 and using phy_read_mmd_indirect and phy_write_mmd_indirect?

I think we can and should make the new wrapper functions remain named
phy_*_mmd_indirect and the names of the override functions in the phy
driver ops should be *_mmd_indirect. The override is still for an
indirect access of c45 registers, just an apparently non-standard one.
It is this way in Linux as well.

-Joe


> -Vladimir
> _______________________________________________
> U-Boot mailing list
> U-Boot at lists.denx.de
> https://lists.denx.de/listinfo/u-boot