linux-kernel - Re: [PATCH 5/8] net: ethernet: ti: am65-cpsw: Add support for fixed-link configuration

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Date:   Thu, 15 Sep 2022 14:58:52 +0530
From:   Siddharth Vadapalli <s-vadapalli@...com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
CC:     <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski@...aro.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <vladimir.oltean@....com>,
        <grygorii.strashko@...com>, <vigneshr@...com>, <nsekhar@...com>,
        <netdev@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <kishon@...com>,
        <s-vadapalli@...com>
Subject: Re: [PATCH 5/8] net: ethernet: ti: am65-cpsw: Add support for
 fixed-link configuration

Hello Russell,

On 14/09/22 21:39, Russell King (Oracle) wrote:
> On Wed, Sep 14, 2022 at 03:20:50PM +0530, Siddharth Vadapalli wrote:
>> Check for fixed-link in am65_cpsw_nuss_mac_config() using struct
>> am65_cpsw_slave_data's phy_node property to obtain fwnode. Since
>> am65_cpsw_nuss_mac_link_up() is not invoked in fixed-link mode, perform
>> the relevant operations in am65_cpsw_nuss_mac_config() itself.
> 
> Further to my other comments, you also fail to explain that, when in
> fixed-link SGMII mode, you _emulate_ being a PHY - which I deduce
> since you are sending the duplex setting and speed settings via the
> SGMII control word. Also, as SGMII was invented for a PHY to be able
> to communicate the media negotiation resolution to the MAC, SGMII
> defines that the PHY fills in the speed and duplex information in
> the control word to pass it to the MAC, and the MAC acknowledges this
> information. There is no need (and SGMII doesn't permit) the MAC to
> advertise what it's doing.
> 
> Maybe this needs to be explained in the commit message?

I had tested SGMII fixed-link mode using a bootstrapped ethernet layer-1
PHY. Based on your clarification in the previous mails that there is an
issue with the fixed-link mode which I need to debug, I assume that what
you are referring to here also happens to be a consequence of that.
Please let me know if I have misunderstood what you meant to convey.

Regards,
Siddharth.