On Mon, May 14, 2018 at 04:10:58AM +0800, Icenowy Zheng wrote: > > > 于 2018年5月14日 GMT+08:00 上午4:05:29, Andrew Lunn <andrew@xxxxxxx> 写到: > >> > Hi Chen-Yu > >> > > >> > Are these delays the MAC applies? Not the PHY. It would be good to > >> > make it clear here these are MAC imposed delays. > >> > >> Yes these are applied on the MAC side. Being described in the device > >> tree bindings for the MAC, I thought this was implied to be the case? > >> Are there known exceptions? > > > >There is frequent confusion with this. Most of the time, the PHY does > >the delay, not the MAC, based on the phy-mode. So the MAC doing it is > >an exception in itself. > > > >Do you actually need these delays for the board you adding support > >for? Does the PHY not support adding the needed delays? If you don't > >need the delays, i would not even implement them. > > They are needed if the rx/tx have not equal length. > > For several boards if the delay is not present, the network > is unusable. (I have at least met this on Banana Pi M3, an > Allwinner A83T SBC w/ RTL8211E) The RTL8211E does not appear to support adding delays, via registers. You can do it with strapping resistors. The RTL8211F does support delays via a register. So for the Banana Pi M3 it is justified. However, in general, i would recommend letting the PHY do it, if it can. Andrew -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
