On Tue, Apr 15, 2025 at 12:18:01PM +0200, Matthias Schiffer wrote: > As discussed [1], the comments for the different rgmii(-*id) modes do not > accurately describe what these values mean. > > As the Device Tree is primarily supposed to describe the hardware and not > its configuration, the different modes need to distinguish board designs If the Ethernet-Controller (MAC) is integrated in an SoC (as is the case with CPSW Ethernet Switch), and, given that "phy-mode" is a property added within the device-tree node of the MAC, I fail to understand how the device-tree can continue "describing" hardware for different board designs using the same SoC (unchanged MAC HW). How do we handle situations where a given MAC supports various "phy-modes" in HW? Shouldn't "phy-modes" then be a "list" to technically descibe the HW? Even if we set aside the "rgmii" variants that this series is attempting to address, the CPSW MAC supports "sgmii", "qsgmii" and "usxgmii/xfi" as well. > (if a delay is built into the PCB using different trace lengths); whether > a delay is added on the MAC or the PHY side when needed should not matter. > > Unfortunately, implementation in MAC drivers is somewhat inconsistent > where a delay is fixed or configurable on the MAC side. As a first step > towards sorting this out, improve the documentation. > > Link: https://lore.kernel.org/lkml/d25b1447-c28b-4998-b238-92672434dc28@xxxxxxx/ [1] > Signed-off-by: Matthias Schiffer <matthias.schiffer@xxxxxxxxxxxxxxx> > --- > .../bindings/net/ethernet-controller.yaml | 16 +++++++++------- > 1 file changed, 9 insertions(+), 7 deletions(-) > > diff --git a/Documentation/devicetree/bindings/net/ethernet-controller.yaml b/Documentation/devicetree/bindings/net/ethernet-controller.yaml > index 45819b2358002..2ddc1ce2439a6 100644 > --- a/Documentation/devicetree/bindings/net/ethernet-controller.yaml > +++ b/Documentation/devicetree/bindings/net/ethernet-controller.yaml > @@ -74,19 +74,21 @@ properties: > - rev-rmii > - moca > > - # RX and TX delays are added by the MAC when required > + # RX and TX delays are part of the board design (through PCB traces). MAC > + # and PHY must not add delays. > - rgmii > > - # RGMII with internal RX and TX delays provided by the PHY, > - # the MAC should not add the RX or TX delays in this case > + # RGMII with internal RX and TX delays provided by the MAC or PHY. No > + # delays are included in the board design; this is the most common case > + # in modern designs. > - rgmii-id > > - # RGMII with internal RX delay provided by the PHY, the MAC > - # should not add an RX delay in this case > + # RGMII with internal RX delay provided by the MAC or PHY. TX delay is > + # part of the board design. > - rgmii-rxid > > - # RGMII with internal TX delay provided by the PHY, the MAC > - # should not add an TX delay in this case > + # RGMII with internal TX delay provided by the MAC or PHY. RX delay is > + # part of the board design. Since all of the above is documented in "ethernet-controller.yaml" and not "ethernet-phy.yaml", describing what the "MAC" should or shouldn't do seems accurate, and modifying it to describe what the "PHY" should or shouldn't do seems wrong. > - rgmii-txid > - rtbi > - smii Regards, Siddharth.
