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Message-ID: <20240508110729.GD1385281@ragnatech.se>
Date: Wed, 8 May 2024 13:07:29 +0200
From: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
To: Andrew Lunn <andrew@...n.ch>
Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Subject: Re: [net-next,v2] net: ethernet: rtsn: Add support for Renesas
Ethernet-TSN
On 2024-05-08 02:35:27 +0200, Andrew Lunn wrote:
> > > This looks wrong. You should be applying delays for rgmii-id and
> > > rgmii-rxid. Plain rgmii means no delays are required, because the
> > > board has extra long clock lines. Same for TX delays, only for
> > > rgmii-tx or rgmii-id.
> >
> > This confuses me a bit, from the bindings in ethernet-controller.yaml I
> > get this the other way around,
> >
> > # RX and TX delays are added by the MAC when required
> > - rgmii
> >
> > # RGMII with internal RX and TX delays provided by the PHY,
> > # the MAC should not add the RX or TX delays in this case
> > - rgmii-id
> >
> > # RGMII with internal RX delay provided by the PHY, the MAC
> > # should not add an RX delay in this case
> > - rgmii-rxid
> >
> > # RGMII with internal TX delay provided by the PHY, the MAC
> > # should not add an TX delay in this case
> > - rgmii-txid
> >
> > The way I understand it is that if if the phy-mode is 'rgmii' the MAC
> > shall apply delays if requested and only if the phy-mode is 'rgmii-id'
> > shall the MAC completely ignore the delays and let the PHY handle it.
>
> It is confusing, and made worse by you doing different to normal and
> implementing it in the MAC, not the PHY.
>
> 1% of boards use extra long clock lines, so don't need additional
> delays. They use 'rgmii'. There is at least one board i know of which
> has one extra long clock line, and one normal length clock line. That
> board uses 'rgmii-txid', or 'rgmii-rxid', i don't remember which. The
> other 98% of boards should be using 'rgmii-id', indicating something
> needs to insert delays. Of those 98%, the vast majority pass phy-mode
> straight to the PHY, and the PHY added delays in both the Rx and Tx
> clock. If the MAC decides to add the delays, and it is 'rgmii-id', it
> should enable delays for both clock lines, and pass 'rgmii' to the
> PHY. In the unlikely event somebody builds one of those 2% boards
> using the MAC, you need to enable just Rx delays, or just Tx delays,
> or maybe no delay at all, because of extra long clock lines. But you
> should still be passing 'rgmii' to the PHY.
Thanks for your patience and this explanation, I understand now.
>
> > Just so I understand correctly, if the phy-mode is A I should pass B to
> > of_phy_connect() if I apply the delays in the MAC.
> >
> > A B
> > rgmii rgmii-id
> > rgmii-id rgmii
> > rgmii-rxid rgmii-txid
> > rgmii-txid rgmii-rxid
>
> Nope. Since the MAC is doing the delay, you always pass rgmii to the
> PHY. A determines what, if any, delays the MAC adds.
>
> Andrew
--
Kind Regards,
Niklas Söderlund
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