linux-kernel - Re: [PATCH v2 1/3] net: phy: at803x: add QCA8084 ethernet phy support

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Message-ID: <20231110101841.27aba547@fedora>
Date:   Fri, 10 Nov 2023 10:18:41 +0100
From:   Maxime Chevallier <maxime.chevallier@...tlin.com>
To:     Jie Luo <quic_luoj@...cinc.com>
Cc:     <andrew@...n.ch>, <hkallweit1@...il.com>, <linux@...linux.org.uk>,
        <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] net: phy: at803x: add QCA8084 ethernet phy
 support

On Fri, 10 Nov 2023 16:53:39 +0800
Jie Luo <quic_luoj@...cinc.com> wrote:

> On 11/9/2023 5:16 PM, Maxime Chevallier wrote:
> > Hello,
> > 
> > On Thu, 9 Nov 2023 16:32:36 +0800
> > Jie Luo <quic_luoj@...cinc.com> wrote:
> > 
> > [...]
> >   
> >>> What I understand from this is that this PHY can be used either as a
> >>> switch, in which case port 4 would be connected to the host interface
> >>> at up to 2.5G, or as a quad-phy, but since it uses QUSGMII the link
> >>> speed would be limited to 1G per-port, is that correct ?  
> >>
> >> When the PHY works on the interface mode QUSGMII for quad-phy, all 4
> >> PHYs can support to the max link speed 2.5G, actually the PHY can
> >> support to max link speed 2.5G for all supported interface modes
> >> including qusgmii and sgmii.  
> > 
> > I'm a bit confused then, as the USGMII spec says that Quad USGMII really
> > is for quad 10/100/1000 speeds, using 10b/8b encoding.
> > 
> > Aren't you using the USXGMII mode instead, which can convey 4 x 2.5Gbps
> >   with 66b/64b encoding ?
> > 
> > Thanks,
> > 
> > Maxime  
> 
> Hi Maxime,
> Yes, for quad PHY mode, it is using 66b/64 encoding.
> 
> it seems that PHY_INTERFACE_MODE_USXGMII is for single port,
> so i take the interface name PHY_INTERFACE_MODE_QUSGMII for
> quad PHYs here.

I see, when I added the QUSGMII mode I wrongly stated that it came from
the USXGMII spec where it really comes from USGMII, my bad.

> can we apply PHY_INTERFACE_MODE_USXGMII to quad PHYs in this
> case(qca8084 quad PHY mode)?

From what I can see, the USXGMII mode in the kernel is used as the
single-port 10G mode of usxgmii. You might need to create a new mode
for quad usxgmii at 10G, the spec calls it 10G-QXGMII I think, but as
the spec defines quite a lot of modes, should we define all of them or
rely on some other parameters to select the actual mode ?

Andrew, Heiner, Russell, what do you think ?

Maxime

> Thanks,
> Jie.