linux-kernel - Re: [PATCH v3] net: phy: add driver for Motorcomm yt8511 phy

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Date:   Fri, 14 May 2021 16:52:26 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Peter Geis <pgwipeout@...il.com>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>
Subject: Re: [PATCH v3] net: phy: add driver for Motorcomm yt8511 phy

> > I also wonder about bits 15:12 of PHY EXT ODH: Delay and driver
> > strength CFG register.
> 
> The default value *works*, and from an emi perspective we want the
> lowest strength single that is reliable.

I was not meaning signal strength, but Txc_delay_sel_fe,

  selecte tx_clk_rgmii delay in chip which is used to latch txd_rgmii
  in 100BT/10BTe mode. 150ps step. Default value 15 means about 2ns
  clock delay compared to txd_rgmii in typical cornor.

[Typos courtesy of the datasheet, not me!]

This sounds like more RGMII delays. It seems like PHY EXT 0CH is about
1G mode, and PHY EXT 0DH is about 10/100 mode. I think you probably
need to set this bits as well. Have you tested against a link peer at
10 Half? 100 Full?

   Andrew