Re: [PATCH 07/12] dt-bindings: net: Add StarFive JH7100 SoC

[Cristian Ciocaltea]

On 2/17/23 15:30, Andrew Lunn wrote:
> > > I would actually say it shows we don't understand what is going on
> > > with delays. "rgmii" is not every often the correct value. The fact it
> > > works suggests the MAC is adding delays.
> > >
> > > What value are you using for starfive,gtxclk-dlychain ?
> >
> > This is set to '4' in patch 12/12.
> >
> > > Try 0 and then "rgmii-id"
> >
> > I made some more tests and it seems the only stable configuration is "rgmii"
> > with "starfive,gtxclk-dlychain" set to 4:
> >
> > phy-mode | dlychain | status
> > ---------+----------+--------------------------------------------
> > rgmii    |        4 | OK (no issues observed)
> > rgmii-id |        4 | BROKEN (errors reported [1])
> > rgmii    |        0 | UNRELIABLE (no errors, but frequent stalls)
> > rgmii-id |        0 | BROKEN (errors reported)
> >
> > [1] Reported errors in case of BROKEN status:
> > $ grep '' /sys/class/net/eth0/statistics/* | grep -v ':0$'
>
> Thanks for the testing.
>
> So it seems like something is adding delays when it probably should
> not. Ideally we want to know what.
>
> There is a danger here, something which has happened in the past. A
> PHY which ignored "rgmii" and actually did power on defaults which was
> "rgmii-id". As a result, lots of boards put "rmgii" in there DT blob,
> which 'worked'. Until a board came along which really did need
> "rgmii". The developer bringing that board up debugged the PHY, found
> the problem and made it respect "rgmii" so their board worked. And the
> fix broke a number of 'working' boards which had the wrong "rgmii"
> instead of "rgmii-id".

Thanks for the heads-up.

> So you have a choice. Go with 4 and "rgmii", but put in a big fat
> warning, "Works somehow but is technically wrong and will probably
> break sometime in the future". Or try to understand what is really
> going on here, were are the delays coming from, and fix the issue.
>
>        Andrew

I will try to analyze this further.

Regards,
Cristian