RE: [PATCH v2 2/2] net: ethernet: Add driver for Sunplus SP7021

Hi Andrew,

I set phy-id registers to 30 and 31 and found the read-back
values of mdio read commands from CPU are all 0x0000.

I consulted with an ASIC engineer. She confirmed that if
phy-id of a mdio command from CPU does not match any 
phy-id registers, the mdio command will not be sent out.

She explained if phy-id of a mdio command does not match 
any phy-id registers (represent addresses of external PHYs),
why MAC needs to send a command to non-existing PHY?


Best regards,

Wells Lu
呂芳騰

智能運算專案/Smart Computing Program
家庭平台事業群/Home Entertainment Business Unit
凌陽科技/Sunplus Technology Co., Ltd.
地址：300新竹科學園區創新一路19號
19, Innovation 1st Road,
Science-based Industrial Park
Hsin-Chu, Taiwan 300
TEL：886-3-5786005 ext. 2580

-----Original Message-----
From: Andrew Lunn <andrew@lunn.ch>
Sent: Thursday, November 25, 2021 11:21 PM
To: Wells Lu 呂芳騰 <redacted>
Cc: Wells Lu <wellslutw@gmail.com>; davem@davemloft.net; kuba@kernel.org;
robh+dt@kernel.org; netdev@vger.kernel.org; devicetree@vger.kernel.org;
linux-kernel@vger.kernel.org; p.zabel@pengutronix.de; Vincent Shih 施錕鴻
[off-list ref]
Subject: Re: [PATCH v2 2/2] net: ethernet: Add driver for Sunplus SP7021

quoted

Due to hardware design, we still need to set PHY address, because MDIO
controller of SP7021 only sends out MDIO commands with the same
address listed in PHY address registers. The function below needs to
be kept.

I suggest you actually set it to some other address. One of the good/bad things about MDIO
is you have no idea if the device is there. A read to a device which does not exist just
returns 0xffff, not an error. So i would set the address of 0x1f. I've never seen a PHY
actually use that address.

    Andrew