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

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Message-ID: <5b9d79f1-ccdd-47c3-a02a-5ff0b12c1fb8@lunn.ch>
Date: Tue, 19 Nov 2024 01:59:54 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Daniel Machon <daniel.machon@...rochip.com>
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

On Fri, Nov 15, 2024 at 09:22:37AM +0000, Daniel Machon wrote:
> 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.

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?

	Andrew