On Wed, 17 Jun 2020 at 13:56, Russell King - ARM Linux admin <li...@armlinux.org.uk> wrote: > > On Tue, Jun 16, 2020 at 09:49:56AM +0200, Helmut Grohne wrote: > > The macb driver does not support configuring rgmii delays. At least for > > the Zynq GEM, delays are not supported by the hardware at all. However, > > the driver happily accepts and ignores any such delays. > > > > When operating in a mac to phy connection, the delay setting applies to > > the phy. Since the MAC does not support delays, the phy must provide > > them and the only supported mode is rgmii-id. However, in a fixed mac > > to mac connection, the delay applies to the mac itself. Therefore the > > only supported rgmii mode is rgmii. > > This seems incorrect - see the phy documentation in > Documentation/networking/phy.rst: > > * PHY_INTERFACE_MODE_RGMII: the PHY is not responsible for inserting any > internal delay by itself, it assumes that either the Ethernet MAC (if > capable > or the PCB traces) insert the correct 1.5-2ns delay > > * PHY_INTERFACE_MODE_RGMII_TXID: the PHY should insert an internal delay > for the transmit data lines (TXD[3:0]) processed by the PHY device > > * PHY_INTERFACE_MODE_RGMII_RXID: the PHY should insert an internal delay > for the receive data lines (RXD[3:0]) processed by the PHY device > > * PHY_INTERFACE_MODE_RGMII_ID: the PHY should insert internal delays for > both transmit AND receive data lines from/to the PHY device > > Note that PHY_INTERFACE_MODE_RGMII, the delay can be added by _either_ > the MAC or by PCB trace routing. >
What does it mean "can" be added? Is it or is it not added? As a MAC driver, what do you do? > The individual RGMII delay modes are more about what the PHY itself is > asked to do with respect to inserting delays, so I don't think your > patch makes sense. > We all read the phy-mode documentation, but we aren't really any smarter. That document completely fails to address the existence of PCB traces. Helmut's link points to some more discussion around this topic. > -- > RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ > FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
