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

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Date:   Fri, 10 Nov 2023 17:56:09 +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 5:33 PM, Maxime Chevallier wrote:
> On Fri, 10 Nov 2023 17:17:58 +0800
> Jie Luo <quic_luoj@...cinc.com> wrote:
> 
>> 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).
> 
> Yes you do need a way to know which mode to use, what I'm wondering is
> that the usxgmii spec actually defines something like 9 different modes
> ( 1/2/4/8 ports, with a total bandwidth ranging from 2.5Gbps to 20 Gbps
> ), should we define a phy mode for all of these variants, or should we
> have another way of getting the mode variant (like, saying I want to
> use usxgmii, in 4 ports mode, with the serdes at 10.3125Gbps).
> 
> That being said, QUSGMII already exists to define a specific variant of
> USGMII, so maybe adding 10G-QXGMII is fine...

Yes, Maxime, I agree with this solution, the name 10G-QXGMII is exactly
the working mode of qca8084 quad phy mode.

> 
> Also, net-next is still currently closed.

Ok, thanks for this reminder.