linux-kernel - Re: [PATCH 0/6] arm64: dts: imx: Move Ethernet aliases out of SoC DTSI

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Message-ID: <aca3addbe510c58524af8d3fd069fe2ae4b1cd24.camel@pengutronix.de>
Date: Tue, 29 Apr 2025 17:43:26 +0200
From: Lucas Stach <l.stach@...gutronix.de>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, Krzysztof
 Kozlowski <krzk@...nel.org>, Rob Herring <robh@...nel.org>, Krzysztof
 Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, Shawn
 Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>,
 Pengutronix Kernel Team <kernel@...gutronix.de>, Fabio Estevam
 <festevam@...il.com>
Cc: devicetree@...r.kernel.org, Francesco Dolcini <francesco@...cini.it>, 
	imx@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux@...tq-group.com
Subject: Re: [PATCH 0/6] arm64: dts: imx: Move Ethernet aliases out of SoC
 DTSI

Am Dienstag, dem 29.04.2025 um 17:17 +0200 schrieb Krzysztof Kozlowski:
> On 29/04/2025 17:13, Lucas Stach wrote:
> > Am Dienstag, dem 29.04.2025 um 16:30 +0200 schrieb Krzysztof Kozlowski:
> > > On 29/04/2025 11:39, Lucas Stach wrote:
> > > > Hi Krzysztof,
> > > > 
> > > > Am Freitag, dem 25.04.2025 um 21:48 +0200 schrieb Krzysztof Kozlowski:
> > > > > Not tested on hardware.
> > > > > 
> > > > > Ethernet interface, like other exposed interfaces, aliases depend on
> > > > > actual board configuration, e.g. its labeling, thus aliases should be
> > > > > defined per each board or each SoM.
> > > > > 
> > > > > Some boards (e.g. Gateworks) follow this convention but many do not.
> > > > > 
> > > > > This is continuation of my comments from:
> > > > > https://lore.kernel.org/r/16a98816-f43c-4f4d-940e-9da30cb1f73f@kernel.org
> > > > > 
> > > > The i.MX boards have traditionally listed aliases for many hardware
> > > > peripherals with the same numbering that's used in the SoC reference
> > > 
> > > ... which is not correct. Aliases should represent how boards are really
> > > labeled, not how reference manual labels them.
> > > 
> > While that is the commonly agreed interpretation today, I do not see
> > any language in the DT spec itself or kernel Documentation/devicetree
> > that would mandate aliases to be used in this way.
> > 
> > In fact there are examples to the contrary like
> > Documentation/devicetree/bindings/serial/samsung_uart.yaml which says:
> > "Each Samsung UART should have an alias [...] as specified by User's
> > Manual of respective SoC."
> 
> And that is an ABI. Did I affect ABI here?
> 
> > 
> > So I would argue that there is no hard line between correct/incorrect
> > for the historical usage of the alias nodes on the i.MX platform.
> 
> There is. ABI is documented. There are things which turn out ABI, even
> though they are not documented, like node names. Was there a problem
> with refactoring these in NXP?
> 
> No.
> 
In fact there was significant fallout from the node name changes, as
assumptions in bootloader code on how to fix up DTs passed to the
kernel were invalidated. We did not make a fuzz about those cases and
just fixed the breakage in the bootloader, because we agreed with the
overall benefit of those changes to the i.MX ecosystem.
> 
> > 
> > > > manual. Boards always have the option to override those aliases if they
> > > > have a good reason to do so, e.g. labeling on the physical device.
> > > > 
> > > > Other users besides Linux rely on fixed numbering provided by the
> > > > aliases. Both barebox and U-Boot number their ethernet interfaces
> > > > according to the alias.
> > > 
> > > And?
> > > 
> > Some usecases depend on the aliases being the same between kernel and
> > bootloader. Historically that has been guaranteed on the i.MX platform
> > by the aliases in the SoC DTSI, when the board didn't have a need to
> 
> I know.
> 
> > change them. With this series applied some other users may now end up
> > with missing aliases if the only include the DTSI.
> 
> Bring actual case, what is broken by this changeset.
> 
> > 
> > > > 
> > > > While you seem to add back aliases for in-tree boards, this breaks the
> > > > majority of boards that include the kernel DTSI from an out-of-tree
> > > > board. I can understand that we can't always accommodate these users,
> > > 
> > > This is not ABI, so every out of tree user is on their own.
> > 
> > I am not too sympathetic about out-of-tree users myself, but I don't
> > think we should make their life harder deliberately.
> 
> We are making our life easier by maintaining and improving source code:
> e.g. not creating fake aliases for devices which do not exist on given
> board.

Sorry, I disagree with this sweeping statement when looking at the
specific changes in this patchset. I simply do not see how this change
significantly improves future maintenance of existing DTs for the i.MX
platform to justify the breakage inflicted upon existing OOT users.

I'm not the one to decide whether or not to take those patches, but
IMHO the overall benefit of those patches to the i.MX ecosystem is not
a net positive.

Regards,
Lucas