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

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Date:   Fri, 26 Nov 2021 03:56:28 +0000
From:   Wells Lu 呂芳騰 <wells.lu@...plus.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     Wells Lu <wellslutw@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        Vincent Shih 施錕鴻 <vincent.shih@...plus.com>
Subject: 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@...n.ch>
> Sent: Thursday, November 25, 2021 11:21 PM
> To: Wells Lu 呂芳騰 <wells.lu@...plus.com>
> Cc: Wells Lu <wellslutw@...il.com>; davem@...emloft.net; kuba@...nel.org;
> robh+dt@...nel.org; netdev@...r.kernel.org; devicetree@...r.kernel.org;
> linux-kernel@...r.kernel.org; p.zabel@...gutronix.de; Vincent Shih 施錕鴻
> <vincent.shih@...plus.com>
> Subject: Re: [PATCH v2 2/2] net: ethernet: Add driver for Sunplus SP7021
> 
> > 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