On Mon, Feb 19, 2024 at 02:29:36PM +0100, Köry Maincent wrote: > On Fri, 16 Feb 2024 10:09:36 -0800 > Rahul Rameshbabu <rrameshbabu@xxxxxxxxxx> wrote: > > > On Fri, 16 Feb, 2024 16:52:22 +0100 Kory Maincent <kory.maincent@xxxxxxxxxxx> > > wrote: > > > Change the API to select MAC default time stamping instead of the PHY. > > > Indeed the PHY is closer to the wire therefore theoretically it has less > > > delay than the MAC timestamping but the reality is different. Due to lower > > > time stamping clock frequency, latency in the MDIO bus and no PHC hardware > > > synchronization between different PHY, the PHY PTP is often less precise > > > than the MAC. The exception is for PHY designed specially for PTP case but > > > these devices are not very widespread. For not breaking the compatibility > > > default_timestamp flag has been introduced in phy_device that is set by > > > the phy driver to know we are using the old API behavior. > > > > > > Signed-off-by: Kory Maincent <kory.maincent@xxxxxxxxxxx> > > > --- > > > > Overall, I agree with the motivation and reasoning behind the patch. It > > takes dedicated effort to build a good phy timestamping mechanism, so > > this approach is good. I do have a question though. In this patch if we > > set the phy as the default timestamp mechanism, does that mean for even > > non-PTP applications, the phy will be used for timestamping when > > hardware timestamping is enabled? If so, I think this might need some > > thought because there are timing applications in general when a > > timestamp closest to the MAC layer would be best. > > This patch comes from a request from Russell due to incompatibility between MAC > and PHY timestamping when both were supported. > https://lore.kernel.org/netdev/Y%2F4DZIDm1d74MuFJ@xxxxxxxxxxxxxxxxxxxxx/ > > His point was adding PTP support to a PHY driver would select timestamp from it > by default even if we had a better timestamp with the MAC which is often the > case. This is an unwanted behavior. > https://lore.kernel.org/netdev/Y%2F6Cxf6EAAg22GOL@xxxxxxxxxxxxxxxxxxxxx/ > > In fact, with the new support of NDOs hwtstamp and the > dev_get/set_hwtstamp_phylib functions, alongside this series which make > timestamp selectable, changing the default timestamp may be not necessary > anymore. > > Russell any thought about it? My position remains: in the case of Marvell PP2 network driver with a Marvell PHY, when we add PTP support for the Marvell PHYs (I have patches for it for years) then we must _not_ regress the existing setup where the PP2 timestamps are the default. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
