Hello, 2016-04-29 20:18 GMT+02:00 Trent Piepho <tpiepho@xxxxxxxxxxxxxx>: > On Fri, 2016-04-29 at 13:00 +0200, Guillermo Rodriguez Garcia wrote: >> 2016-04-28 23:09 GMT+02:00 Trent Piepho <tpiepho@xxxxxxxxxxxxxx>: >> > >> > 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? [1] http://git.pengutronix.de/?p=barebox.git;a=commit;h=ac48b10467ffb1c45e67e5efe36413ede140a498 -- Guillermo Rodriguez Garcia guille.rodriguez@xxxxxxxxx _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
