Subject: Re: [RFC PATCH 5/8] dt-bindings: net: pcs: add bindings for MediaTek USXGMII PCS

From: "Russell King (Oracle)" <[email-masked]>
Date: Mon, 27 Nov 2023 15:47:42 +0000

On Thu, Nov 09, 2023 at 09:51:47PM +0000, Daniel Golle wrote:
> MediaTek's USXGMII can be found in the MT7988 SoC. We need to access
> it in order to configure and monitor the Ethernet SerDes link in
> USXGMII, 10GBase-R and 5GBase-R mode. By including a wrapped
> legacy 1000Base-X/2500Base-X/Cisco SGMII LynxI PCS as well, those
> interface modes are also available.

I think this binding is based on the implementation than on hardware.

What I believe you have is this setup:

        .---- LynxI PCS ----.
MAC ---+                     +--- PEXTP --- world
        `--- USXGMII PCS ---'

You are representing the PEXTP as a separate entity in DT, but then
you're representing the LynxI PCS and the USXGMII PCS as a single
block, which seems to be how you've decided to implement it.

Given that the LynxI PCS is already in use elsewhere in the Mediatek
range, I suggest that the LynxI PCS is one block of IP, and the USXGMII
PCS is a separate block of IP.

1) Would it not be better to model the two PCS seperately?

2) The addition of the SGMII reset needs more information - is this
   controlling a reset for the LynxI block? If so, it should be part
   of a LynxI PCS binding.

3) The PEXTP is presumably a separate block which can be shared between
   several devices - for example, the LynxI, USXGMII, and probably SATA
   and PCIe as well. From the 802.3's network model, the PEXTP is the
   PMA/PMD.

   From the point of view of 802.3's model, a network interface has
   various layers such as the MAC, PCS and PMA/PMD, and sitting above
   these layers is the management of the system. Rather than chasing
   the data flow (which in a network device can be complex) wouldn't
   it be better to continue with the 802.3 model as we are doing with
   other devices, rather than trying to go with a new approach here?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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