From: Holger Brunck <holger.brunck@hitachienergy.com>
To: "Marek Behún" <kabel@kernel.org>
Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
Jakub Kicinski <kuba@kernel.org>, Andrew Lunn <andrew@lunn.ch>
Subject: RE: [v3 2/2] dsa: mv88e6xxx: make serdes SGMII/Fiber output amplitude configurable
Date: Wed, 8 Dec 2021 15:49:19 +0000 [thread overview]
Message-ID: <AM6PR0602MB36717361A85C1B0CA8FE94D0F76F9@AM6PR0602MB3671.eurprd06.prod.outlook.com> (raw)
In-Reply-To: <20211208162852.4d7361af@thinkpad>
> >
> > > > The mv88e6352, mv88e6240 and mv88e6176 have a serdes interface.
> > > > This patch allows to configure the output swing to a desired value
> > > > in the devicetree node of the port. As the chips only supports
> > > > eight dedicated values we return EINVAL if the value in the DTS does not
> match.
> > > >
> > > > CC: Andrew Lunn <andrew@lunn.ch>
> > > > CC: Jakub Kicinski <kuba@kernel.org>
> > > > CC: Marek Behún <kabel@kernel.org>
> > > > Signed-off-by: Holger Brunck <holger.brunck@hitachienergy.com>
> > >
> > > Holger, Andrew,
> > >
> > > there is another issue with this, which I only realized yesterday.
> > > What if the different amplitude needs to be set only for certain SerDes
> modes?
> > >
> > > I am bringing this up because I discovered that on Turris Mox we
> > > need to increase SerDes output amplitude when A3720 SOC is connected
> > > directly to
> > > 88E6141 switch, but only for 2500base-x mode. For 1000base-x, the
> > > default amplitude is okay. (Also when the SOC is connected to
> > > 88E6190, the amplitude does not need to be changed at all.)
> > >
> >
> > on my board I have a fixed link connected with SGMII and there is no
> > dedicated value given in the manual.
> >
> > > I plan to solve this in the comphy driver, not in device-tree.
> > >
> > > But if the solution is to be done in DTS, shouldn't there be a
> > > possibility to define the amplitude for a specific serdes mode only?
> > >
> > > For example
> > > serdes-2500base-x-tx-amplitude-millivolt
> > > or
> > > serdes-tx-amplitude-millivolt-2500base-x
> > > or
> > > serdes-tx-amplitude-millivolt,2500base-x
> > > ?
> > >
> > > What do you think?
> > >
> >
> > in the data sheet for the MV6352 I am using there are no dedicated
> > values stated for different modes at all, they can be chosen
> > arbitrary. So in my case I think it makes sense to keep it as it is
> > for now. Other driver may have other needs and may enhance this later on.
>
> Hi Holger,
>
> but the mv88e6xxx driver also drives switches that allow changing serdes
> modes. There does not need be dedicated TX amplitude register for each serdes
> mode, the point is that we may want to declare different amplitudes for
> different modes.
>
> So the question is: if we go with your binding proposal for the whole mv88e6xxx
> driver, and in the future someone will want to declare different amplitudes for
> different modes on another model, would he need to deprecate your binding or
> would it be easy to extend?
>
ok I see. So if I follow your proposal in my case it would be something like:
serdes-sgmii-tx-amplitude-millivolt to start with ?
I can do that. Andrew what do you think?
Best regards
Holger
next prev parent reply other threads:[~2021-12-08 15:49 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-07 19:07 [v3 1/2] Docs/devicetree: add serdes.yaml Holger Brunck
2021-12-07 19:07 ` [v3 2/2] dsa: mv88e6xxx: make serdes SGMII/Fiber output amplitude configurable Holger Brunck
2021-12-07 19:27 ` Marek Behún
2021-12-08 12:29 ` Holger Brunck
2021-12-08 15:28 ` Marek Behún
2021-12-08 15:49 ` Holger Brunck [this message]
2021-12-08 16:17 ` Marek Behún
2021-12-08 16:21 ` Marek Behún
2021-12-08 16:41 ` Vladimir Oltean
2021-12-08 16:49 ` Vladimir Oltean
2021-12-08 17:00 ` Marek Behún
2021-12-08 17:19 ` Vladimir Oltean
2021-12-08 17:36 ` Marek Behún
2021-12-08 17:55 ` Andrew Lunn
2021-12-08 18:15 ` Marek Behún
2021-12-08 16:51 ` Marek Behún
2021-12-08 16:59 ` Vladimir Oltean
2021-12-08 17:10 ` Marek Behún
2021-12-08 17:12 ` Marek Behún
2021-12-08 17:20 ` Vladimir Oltean
2021-12-08 17:00 ` Andrew Lunn
2021-12-08 17:16 ` Marek Behún
2021-12-15 10:27 ` Holger Brunck
2021-12-15 20:53 ` Marek Behún
2022-01-20 7:52 ` Holger Brunck
2022-01-20 17:57 ` Marek Behún
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