> I'm hoping that Andrew will read my email form yesterday and reconsider > because to me this is a backwards step I will get back to that in a minute. > > On Linux, there currently isn't a way for the MAC driver to query from the PHY > > whether it could include the delays itself. My assumption is that most PHYs > > either don't have internal delays, or the delays are configurable. > > motorcomm, dp83tg720, icplus, marvell, dp 838678, adin, micrel, tja11xx, > vitesse, dp83822, mscc, at803x, microchip_t1, broadcom, dp83869, > intel-xway, realtek all do handle internal delays. I haven't checked > whether there are PHYs that don't - that's harder because we don't know > whether PHYs that don't mention RGMII in the driver actually support > RGMII or not. I did look through this once. There are no PHYs with Linux drivers which support any of the RGMII without supporting all 4 RGMII modes. So we should just assume all RGMII PHYs can add the delays. If i remember the history correctly, Renesas built an RDK with a PHY which did not support RGMII delays. So they where forced to do the delays in the MAC. But it seems like mainline support for that PHY never happened. > > > If this is > > the case, having the MAC add them in internal-delay modes and not adding them on > > the PHY side would be the best default (also for PHY-less/fixed-link setups, > > which should be handled like a PHY without internal delay capabilities.) > > See my "advanced" use case above. We do have drivers doing that. I agree with Russell here, it is the worse default, not the best default. It makes it different to nearly every other MAC driver. It needs extra work in the MAC, which most MAC drivers get wrong. They also tend not to call out they have done it different to every other MAC driver in Linux, and so it does not get the needed extra review, and so is broken. I also think there is some 'vendor SDK' mentality here. Our MAC can do this, our SDK allows it, the Linux driver must have it and use it. Pretty much all hardware has features which never get used, but vendors sometimes have issues with just leaving it unused. Andrew
