netdev - Re: Ethernet not working on a different SoC with same eth HW

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Message-ID: <7b10d4f3-68be-f5d7-633b-21854532ac26@gmail.com>
Date:   Fri, 4 Nov 2016 09:45:41 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Måns Rullgård <mans@...sr.com>,
        Andrew Lunn <andrew@...n.ch>
Cc:     Mason <slash.tmp@...e.fr>, netdev <netdev@...r.kernel.org>,
        Timur Tabi <timur@...eaurora.org>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Zefir Kurtisi <zefir.kurtisi@...atec.com>,
        Martin Blumenstingl <martin.blumenstingl@...il.com>,
        Uwe Kleine-Konig <u.kleine-koenig@...gutronix.de>,
        Daniel Mack <zonque@...il.com>,
        Sebastian Frias <sf84@...oste.net>
Subject: Re: Ethernet not working on a different SoC with same eth HW



On 11/04/2016 08:22 AM, Måns Rullgård wrote:
> Andrew Lunn <andrew@...n.ch> writes:
> 
>> On Fri, Nov 04, 2016 at 03:05:00PM +0000, Måns Rullgård wrote:
>>> Andrew Lunn <andrew@...n.ch> writes:
>>>
>>>>>> I agree with you. But fixing it is likely to break boards which
>>>>>> currently have "rgmii", but actually need the delay in order to work.
>>>>>
>>>>> Does the internal delay here refer to the PHY or the MAC?  It's a
>>>>> property of the MAC node after all.
>>>>
>>>> It is the PHY which applies the delay.
>>>
>>> Says who?
>>
>> The source code.
> 
> There's source code that disagrees with that.  The Broadcom GENET
> driver, for instance.

Correct, and in the case where the MAC adds the delay while transmitting
(because it supports that) the expectation is that the PHY would remove
such a delay internally, conversely, the PHY would introduce a delay
while transmitting back to the PHY, in order to produce the desired 90
degrees shift on the RGMII signals, and get reproduce the correct clock
and data alignment internally.

> 
>>>  Some MACs can do it too.
>>
>> I'm sure they can. But look at the code. Nearly none do, and those
>> that do are potentially broken.
> 
> Those few drivers that do anything differently based on these values
> enable clock delay in the MAC.  That's why I wrote the NB8800 driver the
> way I did.
> 

I don't really what is wrong with the nb8800 driver at the moment, so
maybe this is just a configuration issue with the Atheros PHY driver,
it's not like it has not given people headache judging by the recent
discussions...
-- 
Florian