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

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Date: Fri, 10 Nov 2023 16:53:39 +0800
From: Jie Luo <quic_luoj@...cinc.com>
To: Maxime Chevallier <maxime.chevallier@...tlin.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 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.

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

Thanks,
Jie.