Fwd: Micrel KSZ9031RN PHY problem

Guillermo Rodriguez Garcia guille.rodriguez at gmail.com
Wed May 4 03:39:49 PDT 2016

2016-05-04 9:43 GMT+02:00 Sascha Hauer <s.hauer at pengutronix.de>:
> On Tue, May 03, 2016 at 04:40:02PM +0200, Guillermo Rodriguez Garcia wrote:
>> Hello,
>> 2016-04-29 20:18 GMT+02:00 Trent Piepho <tpiepho at kymetacorp.com>:
>> > On Fri, 2016-04-29 at 13:00 +0200, Guillermo Rodriguez Garcia wrote:
>> >> 2016-04-28 23:09 GMT+02:00 Trent Piepho <tpiepho at kymetacorp.com>:
>> >> >
>> >> > The first anreg start call will also un-powerdown the PHY if BMCR_PDOWN
>> >> > was set.  I wonder if that is happening?
>> >>
>> >> That was a very good hint and it looks like this is exactly what is happening.
>> >>
>> >> genphy_restart_aneg() clears the BMCR_PDOWN bit and would get the phy
>> >> out of powerdown mode. I have added a trace right at the beginning of
>> >> genphy_restart_aneg and verified that BMCR_PDOWN bit was set before
>> >> genphy_restart_aneg clears it.
>> >>
>> >> Then, the datasheet for the ksz9031 [1], page 44, says:
>> >>
>> >> After this bit is changed from '1' to '0', an internal global reset is
>> >> automatically generated. Wait a minimum of 1ms before read/write
>> >> access to the PHY registers.
>> >
>> > Mystery solved!
>> Indeed. Although it's strange that the problem can only be reproduced
>> with certain routers. I can reproduce it everytime when the board is
>> connected with a ComTrend VG-8050, but not with other routers..
>> >
>> >> So this seems to be what is causing the problem. At least on the
>> >> ksz9031 (don't know about others), a delay of 1ms is required when
>> >> coming out of powerdown mode.
>> >
>> > The kernel will take the phy in/out of powerdown mode as part of the PM
>> > suspend/resume calls, which is supported on all micrel phys since 2013.
>> > I don't see a delay in the kernel code and wonder why this hasn't been a
>> > problem?
>> Perhaps this is due to the fact that it does not happen with every router.
>> >  Might be worth asking on net-dev if this is a known issue with
>> > some phys and how it is solved?  Maybe it's an undiscovered cause of
>> > network flakiness after a resume.
>> Would you be willing to help here? (i.e. report/ask about this on net-dev)
>> >
>> >> What is the best way to fix this? We can add a 1ms delay in
>> >> genphy_restart_aneg (this is probably the easiest, and the delay is
>> >> small enough that it shouldn't make a difference for other phys that
>> >> might not need it). Or if this is not acceptable, perhaps add a custom
>> >> restart_aneg function for the ksz9031.
>> >
>> > Could add a custom init function that un-powerdowns the phy and does the
>> > wait.
>> >
>> > Or have restart_aneg check if the powerdown bit was set before it clears
>> > it, and only delay in that case.
>> This would be easy, would solve the problem at hand, and would only
>> introduce a (perhaps unnecessary) 1ms delay for phys that don't need
>> this.
>> >
>> > Having the un-powerdown in the restart_aneg isn't really the right place
>> > for it.  If there is no reason the restart aneg, then the phy will not
>> > be powered up.
>> Yes but I would say that that's a different issue. I must say I don't feel
>> confident enough to move this code to somewhere else myself. Perhaps
>> Sascha (as the original author of this change [1]) could comment.
>> I would suggest so separate these two issues: 1) Adding the missing
>> 1ms delay as described in the Micrel datasheet, 2) Consider whether
>> the code should be refactored / reorganized.
>> Does this make sense?
> Yes, makes sense.
> Currently I don't know a better place for clearing the BMCR_PDOWN bit.
> genphy_config_init would be a candidate, but it's not called for phys
> which have a custom .config_init hook.
> If I'm lucky I can find the ethernet adapter which motivated me to
> create ac48b10467ffb, it would be interesting to see which phy type the
> adapter has.

For what it's worth, the Micrel ksz9031 in my SAMA5D3 Xplained board
also seems to come up with the BMCR_PDOWN bit set (or at least, the
bit is set when genphy_restart_aneg() is called -- I am assuming that
Barebox is not setting this bit itself during init)

Guillermo Rodriguez Garcia
guille.rodriguez at gmail.com

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