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> > > > > > + phy-mode = "rgmii"; /* Delays implemented by the IO ring of the Agilex5 SOCFPGA. */ > > > > > > > Please could you explain in more details what this means. > > > > > > > The normal meaning for 'rgmii' is that the PCB implements the > > > delay. I > > > > > just want to fully understand what this IO ring is, and if it is part > > > > > of the PCB. > > > > > The IO ring is the logic in the Agilex5 that controls the pins on > > > the chip. > > > > It is this logic that sits between the MAC IP in the Agilex5 and the pins > > > > connected to the PCB that is inserting the necessary delays. Technically the > > > > PCB is not implementing the delays, but the "wires" between the MAC and the > > > > external pins of the Agilex5 are implementing the delay. It seems to me that > > > > "rgmii" is a more accurate description of the hardware than "rgmii-id" in > > > > this case. > > > > > > Is this delay hard coded, physically impossible to be disabled? A > > > syntheses option? Can it be changed at run time? Is the IO ring under > > > the control of a pinctrl driver? Can i use the standard 'skew-delay' > > > DT property to control this delay? > > > The delay is not hard coded. It is a synthesis option that can be disabled. > > Is there a register you can read which tells you if it is > enabled/disabled? There are a collection of registers that could be examined to determine if delay has been inserted by IO ring. > > > The delay in the IO ring can be disabled, but implementing the delay in the > > IO ring allows for RGMII phys that don't implement the delay. > > All RGMII PHYs which Linux support have the ability to do delays. And > we recommend the PHY does the delay, just to keep all systems the > same. There are a few exceptions, mostly because the MAC has hard > coded delays which cannot be disabled, but i guess 90% of systems have > the PHY doing the 2ns delays. > > So, phy-mode should be set to 'rgmii-id', since the PCB does not add > the delays. Understood. The PCB is not adding delays; so I'll change the phy-mode to be rgmii-id. > > Ideally, you want to read from the IO ring if it is synthesised to do > the 2ns delays. Assuming it is enabled, you then mask the phy-mode > before connecting to the PHY, so avoiding double delays. > > Andrew > Currently, the registers in question are considered secure and only accessible by Arm Trusted Firmware (ATF). I will investigate implementing this delay detecting logic in a future patchset. Thanks for the feedback, Matthew Gerlach