linux-kernel - Re: [PATCH v6 3/6] net: phy: at803x: add QCA8084 ethernet phy support

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Message-ID: <277a4cdf-fef6-4d40-baac-01d5da40ce62@quicinc.com>
Date:   Wed, 29 Nov 2023 18:34:16 +0800
From:   Jie Luo <quic_luoj@...cinc.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
CC:     Andrew Lunn <andrew@...n.ch>, <davem@...emloft.net>,
        <edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
        <robh+dt@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <conor+dt@...nel.org>, <hkallweit1@...il.com>, <corbet@....net>,
        <netdev@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v6 3/6] net: phy: at803x: add QCA8084 ethernet phy support



On 11/28/2023 6:35 PM, Russell King (Oracle) wrote:
> On Tue, Nov 28, 2023 at 05:50:41PM +0800, Jie Luo wrote:
>>
>>
>> On 11/28/2023 5:00 PM, Russell King (Oracle) wrote:
>>> On Tue, Nov 28, 2023 at 03:16:45PM +0800, Jie Luo wrote:
>>>>>> The interface mode is passed in the .config_init, which is configured
>>>>>> by the PCS driver, the hardware register is located in the PCS, this
>>>>>> driver will be pushed later.
>>>>>
>>>>> Is this the same as how the syqca807x works? Can the PCS driver be
>>>>> shared by these two drivers?
>>>>
>>>> I am not sure syqca807x, would you point me the code path of this driver?
>>>>
>>>>>
>>>>> What i don't like at the moment is that we have two driver
>>>>> developments going on at once for hardware which seems very similar,
>>>>> but no apparent cooperation?
>>>>>
>>>>> 	Andrew
>>>>
>>>> The PCS of qca8084 is the PHY PCS, which should be new PCS driver,
>>>> in the previous chips, we don't have this kind of PHY PCS.
>>>
>>> No. PCS drivers are for MAC-side PCS drivers, not PHY-side PCS drivers.
>>>
>>>                        +-------------
>>> 		     |     PHY
>>> MAC---PCS --- link --- PCS --- ...
>>>          ^             |  ^
>>>          |	     +--|----------
>>>     For this PCS          |
>>>                     Not for this PCS
>>>
>>
>> The PCS drivers in drivers/net/pcs/ should be in PHY side, such as
>> pcs-lynx.c and pcs-xpcs.c, they are configuring the MDIO device
>> registers.
> 
> Wrong. No they are not. Just because they are accessed via MDIO does
> not mean they are in the PHY. MDIO can be used for more than just the
> PHY, and is on a lot of platforms.
> 
> LX2160A for example has many MDIO buses, and the PCSes (of which there
> are multiple inside the chip, and use pcs-lynx) are accessed through
> the MDIO bus specific to each port. They are not MMIO mapped.
> 
> The same is true on stmmac platforms, where xpcs is used - xpcs is the
> _MAC_ side PCS.
> 
> Sorry but you are wrong.
> 

OK, but it creates the PCS driver based on the MDIO device in pcs-lynx.c
looks like this PCS is located in PHY device from hardware perspective.