linux-kernel - Re: [PATCH net-next v1] lan78xx: lan7801 MAC support with lan8841

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Message-ID: <2aa4fba0-c5bd-47e9-97a7-3f73048282cb@lunn.ch>
Date: Fri, 28 Jun 2024 15:03:27 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Rengarajan.S@...rochip.com
Cc: linux-usb@...r.kernel.org, davem@...emloft.net,
	Woojung.Huh@...rochip.com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, pabeni@...hat.com,
	UNGLinuxDriver@...rochip.com, edumazet@...gle.com, kuba@...nel.org
Subject: Re: [PATCH net-next v1] lan78xx: lan7801 MAC support with lan8841

> Although, there is no specific errata available for adding fixup
> specific to lan78xx USB dongle, we have added the fixup for handing
> specific configurations to ensure the PHY operates correctly with the
> MAC. In this case while transmitting from MAC to PHY the device does
> not add the delay locally at its TX input pins. It expects the TXC
> delay to be provided by on-chip MAC. Since the delay calculated in this
> case is specific to the lan78xx USB dongle it is not possible to use
> this fixup for interfacing with generic MAC.

Have you tried PHY_INTERFACE_MODE_RGMII_TXID when connecting to the
PHY? The four PHY_INTERFACE_MODE_RGMII_* values are the official way
to ask the PHY to insert delays, or not. If that is all you are doing,
i don't think you need these fixups at all.

> > Please give me a details explanation why this fixup will not be
> > applied to other instances of this PHY in the system.
> 
> As stated above, the TXC delay calculated for the PHY is specific to
> the lan78xx on-chip MAC. This delay ensures that both the phy and MAC
> clock delay timing is met. Any other MACs connected will need a
> different delay values to be synchronized with MAC and hence these
> instances will get failed.

You did not answer my question. Show me the code path which prevents
this being applied to other PHYs. Is there a comparison to netdev
somewhere when applying the fixup? Give me the file:line number.

	  Andrew