Re: [PATCH RFC net-next 00/15] net: stmmac: rk: cleanups galore

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Andrew Lunn <andrew@lunn.ch>
Cc: Heiner Kallweit <hkallweit1@gmail.com>,
	Alexandre Torgue <alexandre.torgue@foss.st.com>,
	Andrew Lunn <andrew+netdev@lunn.ch>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Heiko Stuebner <heiko@sntech.de>,
	Jakub Kicinski <kuba@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-rockchip@lists.infradead.org,
	linux-stm32@st-md-mailman.stormreply.com,
	Maxime Coquelin <mcoquelin.stm32@gmail.com>,
	netdev@vger.kernel.org, Paolo Abeni <pabeni@redhat.com>
Subject: Re: [PATCH RFC net-next 00/15] net: stmmac: rk: cleanups galore
Date: Mon, 1 Dec 2025 16:38:22 +0000	[thread overview]
Message-ID: <aS3EfuypsaGK6Ww_@shell.armlinux.org.uk> (raw)
In-Reply-To: <05db9d3e-88fa-42db-8731-b77039c60efa@lunn.ch>

On Mon, Dec 01, 2025 at 04:55:21PM +0100, Andrew Lunn wrote:
> > One of the interesting things is that this appears to deal with RGMII
> > delays at the MAC end of the link, but there's no way to tell phylib
> > that's the case. I've not looked deeply into what is going on there,
> > but it is surprising that the driver insists that the delays (in
> > register values?) are provided, but then ignores them depending on the
> > exact RGMII mode selected.
> 
> Yes, many Rockchip .dts files use phy-mode = 'rgmii', and then do the
> delays in the MAC. I've been pushing back on this for a while now, and
> in most cases, it is possible to set the delays to 0, and use
> 'rgmii-id'.
> 
> Unfortunately, the vendor version of the driver comes with a debugfs
> interface which puts the PHY into loopback, and then steps through the
> different delay values to find the range of values which result in no
> packet loss. The vendor documentation then recommends
> phy-mode='rgmii', and set the delays to the middle value for this
> range. So the vendor is leading developers up the garden path.
> 
> These delay values also appear to be magical. There has been at least
> one attempt to reverse engineer the values back to ns, but it was not
> possible to get consistent results across a collection of boards.

Oh yes, I remember that. I also remember that I had asked for the
re-use of "phy_power_on()" to be fixed:

https://lore.kernel.org/netdev/aDne1Ybuvbk0AwG0@shell.armlinux.org.uk/

but that never happened... which makes me wonder whether we *shouldn't*
have applied "sensor101"'s patch until such a requested patch was
available. In my experience, this is the standard behaviour - as a
reviewer, you ask a contributor to do something as part of their
patch submission, and as long as their patch gets merged, they
couldn't give a monkeys about your request.

So, in future, I'm going to take the attitude that I will NAK
contributions if I think there's a side issue that the contributor
should also be addressing until that side issue is addressed.

This shouldn't be necessary, I wish this weren't necessary, and I wish
people could be relied upon to do the right thing, but apparently it is
going to take a stick (not merging their patches) to get them to co-
operate. More fool me for trusting someone to do something.

I now have a couple of extra patches addressing my point raised in
that email... which I myself shouldn't have had to write.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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