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

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Message-ID: <46d61a29-96bf-868b-22b9-a31e48576803@quicinc.com>
Date:   Fri, 10 Nov 2023 17:17:58 +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 11/10/2023 4:53 PM, Jie Luo 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.
> 
> can we apply PHY_INTERFACE_MODE_USXGMII to quad PHYs in this
> case(qca8084 quad PHY mode)?
> 
> Thanks,
> Jie.

one more thing, if we use the PHY_INTERFACE_MODE_USXGMII for
the quad PHY here, the MAC serdes can't distinguish the actual
mode PHY_INTERFACE_MODE_USXGMII and 10G-QXGMII(qca8084 quad phy mode),
the MAC serdes has the different configurations for usxgmii(10g single 
port) and qxsgmii(quad PHY).