netdev - Re: dp83867: Why does ti,fifo-depth set only TX, and why is it mandatory?

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Date:   Tue, 19 Nov 2019 11:35:17 -0600
From:   Dan Murphy <dmurphy@...com>
To:     Adrian Bunk <bunk@...nel.org>
CC:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        <netdev@...r.kernel.org>
Subject: Re: dp83867: Why does ti,fifo-depth set only TX, and why is it
 mandatory?

Adrian

On 11/14/19 2:01 PM, Dan Murphy wrote:
> Adrian
>
> On 11/14/19 1:47 PM, Adrian Bunk wrote:
>> On Thu, Nov 14, 2019 at 11:53:36AM -0600, Dan Murphy wrote:
>>> Adrian
>> Hi Dan,
>>
>>> ...
>>>> 2. Why is it a mandatory property?
>>>> Perhaps I am missing something obvious, but why can't the driver 
>>>> either
>>>> leave the value untouched or set the maximum when nothing is 
>>>> configured?
>>> When the driver was originally written it was written only for RGMII
>>> interfaces as that is the MII that the data sheet references and 
>>> does not
>>> reference SGMII.  We did not have SGMII samples available at that time.
>>> According to the HW guys setting the FIFO depth is required for RGMII
>>> interfaces.
>> My reading of the datasheets is that it isn't needed at all for RGMII,
>> only for SGMII and gigabit GMII.
>>
>> Which makes it weird that it is only written in the RGMII case where it
>> is documented to be disabled.
>>
>> And there is a documented default value so writing shouldn't be 
>> mandatory
>> in any case.
>>
>> Perhaps I am looking at the wrong datasheets or there's a hardware 
>> errata?
>>
>>> When SGMII support was added in commit
>>> 507ddd5c0d47ad869f361c71d700ffe7f12d1dd6
>> That's adding 6-wire mode support, the version of the driver I use with
>> SGMII in 4.14 is much older and not far from the original submission.
>>
>> Is there anything that might be missing for SGMII you are aware of?
>>
> I forwarded this to our PHY support guy as I did not work on the SGMII 
> device they shipped.
>
> I only had a RGMII certified device.

I only got half the info but the FIFO depth is not required for RGMII.  
They are still trying to determine if it is for SGMII

Waiting on a response from someone OoO

Dan


>
> Dan
>