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

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Message-ID: <d20a0c5a-507c-dd75-0951-e0733daf4a6e@ti.com>
Date:   Thu, 14 Nov 2019 14:01:59 -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 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.

Dan