netdev - Re: [PATCH net-next v3 1/7] net: dsa: mt7530: empty default case on mt7530_setup

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Date: Mon, 5 Feb 2024 22:29:35 +0200
From: Vladimir Oltean <olteanv@...il.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Arınç ÜNAL <arinc.unal@...nc9.com>,
	Daniel Golle <daniel@...rotopia.org>,
	DENG Qingfang <dqfext@...il.com>,
	Sean Wang <sean.wang@...iatek.com>, Andrew Lunn <andrew@...n.ch>,
	Florian Fainelli <f.fainelli@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	mithat.guner@...ont.com, erkin.bozoglu@...ont.com,
	Bartel Eerdekens <bartel.eerdekens@...stell8.be>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net-next v3 1/7] net: dsa: mt7530: empty default case on
 mt7530_setup_port5()

On Fri, Feb 02, 2024 at 06:05:36PM +0000, Russell King (Oracle) wrote:
> > > Given everything I've said above, the only way to configure RGMII
> > > delays is via the rx-internal-delay-ps and tx-internal-delay-ps
> > > properties. So, DSA drivers should _not_ be configuring their ports
> > > with RGMII delays based on the RGMII phy interface mode.
> > > 
> > > The above is my purely logically reasoned point of view on this
> > > subject. Others may have other (to me completely illogical)
> > > interpretations that can only lead to interoperability issues.
> > 
> > I will address this with the next patch series. Thank you for explaining it
> > in detail.
> 
> This is a good time to point out not to rush with the next patch
> series, as my email will _likely_ provoke some additional discussion
> from Andrew and/or Vladimir. So please give it a few days (maybe
> around the middle of next week) to give them time to consider my
> email and respond.

I agree with everything you've said. The only problem is that
Documentation/devicetree/bindings/net/ethernet-controller.yaml is
ambiguous on this topic (to put it mildly).

@Arınç, there are ways to handle the "tx-internal-delay-ps" in
mt7530_setup_port5() in a way that is backwards compatible. I don't know
about RX delays - the function doesn't handle them, and I don't have the
time to open datasheets now. You can take inspiration from
ksz_parse_rgmii_delay() and sja1105_parse_rgmii_delays() on how to only
fall back to the current logic to set the tx_delay if the more specific
OF properties are not present.