On Thu, Jan 14, 2021 at 01:22:17PM +0000, Russell King - ARM Linux admin wrote: > On Thu, Jan 14, 2021 at 04:55:06AM -0800, Richard Cochran wrote: > > On Sun, Jan 10, 2021 at 11:13:44AM +0000, Russell King wrote: > > > This allows network drivers such as mvpp2 to use their more accurate > > > timestamping implementation than using a less accurate implementation > > > in the PHY. Network drivers can opt to defer to phylib by returning > > > -EOPNOTSUPP. > > > > My expectation is that PHY time stamping is more accurate than MAC > > time stamping. > > PHY time stamping may be a "more accurate" location to get timestamps, > in terms of the hardware, but when you consider the entire setup, that > is not necessarily the case. > > > > This change will be needed if the Marvell PHY drivers add support for > > > PTP. > > > > Huh? The mvpp2 appears to be a MAC. If this device has integrated > > PHYs then I don't see the issue. If your board has the nvpp2 device > > with the dp83640 PHYTER, then don't you want to actually use the > > PHYTER? > > You seem to be adding more information way beyond what I'm saying. > > No, there aren't integrated PHYs. There's an external PHY - a Marvell > 88e151x which has what I would call rudimentary stamping abilities, > whereas the mvpp2 has advanced stamping abilities. > > You implemented the Marvell timestamping in DSA, so you know what the > Marvell offering there looks like and what it is capable of. That same > hardware appears in some Marvell PHYs. > > The mvpp2 hardware (which has support already merged after you acked > the TAI part, and failed to provide comments on the mvpp2 part - so > davem gave up waiting) is capable of: > - stamping every received packet irrespective of its type > - stamping any transmitted packet or only those we wish to stamp > - inserting a timestamp into the packet (aka one-step, although that > isn't implemented that yet) > - correcting the hardware time counter tick rate > > There is considerable noise in reading the hardware timestamp counter > from the PHYs - caused by latency over the MDIO bus, which makes the > achievable accuracy lower. That noise is very much reduced when reading > the hardware timestamp counter from mvpp2 - where we can implement > mvpp22_tai_gettimex64(). Therefore, the achieved accuracy from mvpp2 is > higher than from a PHY. > > We had already discussed this patch last year, and you agreed with it > then. What has changed?
See the discussion in this sub-thread: https://lore.kernel.org/netdev/20200729105807.gz1...@shell.armlinux.org.uk/ -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
