linux-kernel - Re: [PATCH net-next v2 8/8] dt-bindings: net: sparx5: document RGMII MAC delays

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Message-ID: <20241119114304.u47srawc2t6ymvf6@DEN-DL-M70577>
Date: Tue, 19 Nov 2024 11:43:04 +0000
From: Daniel Machon <daniel.machon@...rochip.com>
To: Andrew Lunn <andrew@...n.ch>
CC: <UNGLinuxDriver@...rochip.com>, Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, "Lars
 Povlsen" <lars.povlsen@...rochip.com>, Steen Hegelund
	<Steen.Hegelund@...rochip.com>, Horatiu Vultur
	<horatiu.vultur@...rochip.com>, Russell King <linux@...linux.org.uk>,
	<jacob.e.keller@...el.com>, <robh@...nel.org>, <krzk+dt@...nel.org>,
	<conor+dt@...nel.org>, <devicetree@...r.kernel.org>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH net-next v2 8/8] dt-bindings: net: sparx5: document RGMII
 MAC delays

> > Hi Andrew,
> >
> > > > The lan969x switch device supports two RGMII port interfaces that can be
> > > > configured for MAC level rx and tx delays.
> > > >
> > > > Document two new properties {rx,tx}-internal-delay-ps. Make them
> > > > required properties, if the phy-mode is one of: rgmii, rgmii_id,
> > > > rgmii-rxid or rgmii-txid. Also specify accepted values.
> > >
> > > This is unusual if you look at other uses of {rt}x-internal-delay-ps.
> > > It is generally an optional parameter, and states it defaults to 0 if
> > > missing, and is ignored by the driver if phy-mode is not an rgmii
> > > variant.
> >
> > Is unusual bad? :-)
> 
> Depends. Having a uniform usage is good, it causes less confusion. But
> strict enforcement also has its plus side.
> 
> > I thought that requiring the properties would make
> > misconfigurations (mismatching phy-modes and MAC delays) more obvious,
> > as you were forced to specify exactly what combination you want in the
> > DT.  Maybe not. I can change it,  no problem.
> 
> Do these ports only support RGMII? The general pattern is that ports
> supporting RGMII also support other modes, GMII, MII, rev-GMII,
> rev-MII etc. For these other modes RGMII delays are meaningless. The
> general pattern is that they are allowed in DT, but are just ignored.

RGMII and RMII.

> 
> If the LAN969x ports only support RGMII, and you are enforcing the
> four RGMII modes in DT, you could also enforce the delays are present
> and only have all allowed values. But i would not have the enforcement
> any more strict than the other ports. Do you enforce the phy-modes for
> the ports with a PCS?

No, we do not enforce that in the DT. For the PCS ports, you can specify
whatever phy-mode in the DT, and if that phy-mode is not advertised in
the driver, it will just be rejected.

I decided to go ahead with v3 (which needs to be reposted when net-next
opens), where the properties are not required.

> 
>         Andrew

Thanks for your feedback.

/Daniel