netdev - Re: [linux-sunxi] Re: [PATCH] net: phy: realtek: omit setting PHY-side delay when "rgmii" specified

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Date:   Sun, 25 Oct 2020 22:27:05 +0800
From:   Icenowy Zheng <icenowy@...c.io>
To:     andrew@...n.ch, Andrew Lunn <andrew@...n.ch>
CC:     Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Willy Liu <willy.liu@...ltek.com>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Rob Herring <robh+dt@...nel.org>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [linux-sunxi] Re: [PATCH] net: phy: realtek: omit setting PHY-side delay when "rgmii" specified



于 2020年10月25日 GMT+08:00 下午10:18:25, Andrew Lunn <andrew@...n.ch> 写到:
>On Sun, Oct 25, 2020 at 04:55:56PM +0800, Icenowy Zheng wrote:
>> Currently there are many boards that just set "rgmii" as phy-mode in
>the
>> device tree, and leave the hardware [TR]XDLY pins to set PHY delay
>mode.
>> 
>> In order to keep old device tree working, omit setting delay for just
>> "RGMII" without any internal delay suffix, otherwise many devices are
>> broken.
>
>Hi Icenowy
>
>We have been here before with the Atheros PHY. It did not correctly
>implement one of the delay modes, until somebody really did need that
>mode. So the driver was fixed. And we then found a number of device
>trees were also buggy. It was painful for a while, but all the device
>trees got fixed.

1. As the PHY chip has hardware configuration for configuring delays,
we should at least have a mode that respects what's set on the hardware.
2. As I know, at least Fedora ships a device tree with their bootloader, and
the DT will not be updated with kernel. This enforces compatibility
with old DTs even if they're broken.

Personally I think if someone wants a mode that explicitly disable delays
in the PHY, a new mode may be created now, maybe called "rgmii-noid".

>
>We should do the same here. Please submit patches for the device tree
>files.
>
>   Andrew