linux-kernel - Re: [PATCH net-next 1/3] net: nixge: Add support for fixed-link subnodes

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Date:   Thu, 30 Aug 2018 14:09:13 -0700
From:   Moritz Fischer <moritz.fischer@...us.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Kees Cook <keescook@...omium.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        netdev@...r.kernel.org, Alex Williams <alex.williams@...com>
Subject: Re: [PATCH net-next 1/3] net: nixge: Add support for fixed-link subnodes

Andrew,

On Thu, Aug 30, 2018 at 10:54 AM, Andrew Lunn <andrew@...n.ch> wrote:
>> > The hardware has MDIO, but you don't have a PHY connected on it, and
>> > use fixed link.
>>
>> Since it's an FPGA design in that case we'd probably build the hardware without
>> MDIO to save resources.
>
> You can save resources, but is it worth the complexity else where,
> like in the software?

Depends. For now I definitely have build versions that don't have MDIO regs
there. I might be able to chat with HW folks ...

>
>> > It is important you have the mdio subnode, with PHYs and switches as
>> > children. The driver currently gets this wrong, it uses
>> > pdev->dev.of_node.
>>
>> Oh, whoops.
>
> Yes, and i also missed it. I generally review all new network drivers
> and look at their MDIO and PHY code.

I had looked at macb as an example and there were a bunch of other cases
where there was no 'mdio' subnode.

>
>> Any good examples of drivers doing it right? Is the one going with
>> the DT snippet above a good example?
>
> That comes from the Freescale fec_main.c. It only supports DT, and
> always uses of_mdiobus_register. You need to be a bit more flexible
> for when you don't have DT. I'm not sure there are good example of
> this, since they either don't need this flexibility, or they get it
> wrong :-(

Alright, no problem. I'll take a stab at it. And come back with a v2 ;-)
Need to look at your response in the other patch.

Cheers,

Moritz