netdev - Re: [PATCH v2 1/3] dt-bindings: net: fsl-fec add mdc/mdio bitbang option

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Message-ID: <bb81c90c-d79e-d944-e35e-305da23d9e58@gmail.com>
Date:   Mon, 30 Nov 2020 14:08:38 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Andrew Lunn <andrew@...n.ch>,
        Adrien Grassein <adrien.grassein@...il.com>
Cc:     fugang.duan@....com, davem@...emloft.net, kuba@...nel.org,
        robh+dt@...nel.org, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] dt-bindings: net: fsl-fec add mdc/mdio bitbang
 option



On 11/29/2020 3:04 PM, Andrew Lunn wrote:
> On Sun, Nov 29, 2020 at 11:51:43PM +0100, Adrien Grassein wrote:
>> Hi Andrew,
>>
>> Please find my answers below.
>>
>> Le dim. 29 nov. 2020 à 23:41, Andrew Lunn <andrew@...n.ch> a écrit :
>>
>>     On Sun, Nov 29, 2020 at 10:59:58PM +0100, Adrien Grassein wrote:
>>     > Add dt-bindings explanation for the two new gpios
>>     > (mdio and mdc) used for bitbanging.
>>
>>     Hi Adrien
>>
>>     What is missing is an explanation of why!
>>
>> I'm sorry, it's my first upstreaming attempt.
> 
> Hi Adrien
> 
> Please take a look at
> 
> https://www.kernel.org/doc/html/latest/networking/netdev-FAQ.html
> 
> It is normal to have a patch 0/X which explains the big picture.
> 
> Then the commit message for each patch should explain why you are
> doing something. That is much more important than what you are doing,
> i can see that from the patch itself.
> 
>> I am currently upstreaming the "Nitrogen 8m Mini board" that seems to not use a
>> "normal" mdio bus but a "bitbanged" one with the fsl fec driver.
> 
> Any idea why?
> 
> Anyway, you should not replicate code, don't copy bitbanging code into
> the FEC. Just use the existing bit-banger MDIO bus master driver.

Right there should be no need for you to modify the FEC driver at all,
there is an existing generic bitbanged MDIO bus driver here:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/mdio/mdio-gpio.c

with its binding here:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/net/mdio-gpio.txt

so all you should need to do is make sure that you place a
"virtual,mdio-gpio" node, declare the PHY devices that are present on
that bus, and have your FEC nodes point to those PHY devices with an
appropriate 'phy-handle' property.
-- 
Florian