linux-kernel - Re: [PATCH net-next 4/4] checkpatch: check for comment explaining rgmii(|-rxid|-txid) PHY modes

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Message-ID: <20250415131548.0ae3b66f@fedora.home>
Date: Tue, 15 Apr 2025 13:15:48 +0200
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: Matthias Schiffer <matthias.schiffer@...tq-group.com>
Cc: 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>, Rob Herring
 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Andy Whitcroft <apw@...onical.com>, Dwaipayan Ray
 <dwaipayanray1@...il.com>, Lukas Bulwahn <lukas.bulwahn@...il.com>, Joe
 Perches <joe@...ches.com>, Jonathan Corbet <corbet@....net>, Nishanth Menon
 <nm@...com>, Vignesh Raghavendra <vigneshr@...com>, Siddharth Vadapalli
 <s-vadapalli@...com>, Roger Quadros <rogerq@...nel.org>, Tero Kristo
 <kristo@...nel.org>, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux@...tq-group.com, Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH net-next 4/4] checkpatch: check for comment explaining
 rgmii(|-rxid|-txid) PHY modes

On Tue, 15 Apr 2025 12:18:04 +0200
Matthias Schiffer <matthias.schiffer@...tq-group.com> wrote:

> Historially, the RGMII PHY modes specified in Device Trees have been
  ^^^^^^^^^^^
  Historically
> used inconsistently, often referring to the usage of delays on the PHY
> side rather than describing the board; many drivers still implement this
> incorrectly.
> 
> Require a comment in Devices Trees using these modes (usually mentioning
> that the delay is relalized on the PCB), so we can avoid adding more
> incorrect uses (or will at least notice which drivers still need to be
> fixed).
> 
> Suggested-by: Andrew Lunn <andrew@...n.ch>
> Signed-off-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>
> ---
>  Documentation/dev-tools/checkpatch.rst |  9 +++++++++
>  scripts/checkpatch.pl                  | 11 +++++++++++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
> index abb3ff6820766..8692d3bc155f1 100644
> --- a/Documentation/dev-tools/checkpatch.rst
> +++ b/Documentation/dev-tools/checkpatch.rst
> @@ -513,6 +513,15 @@ Comments
>  
>      See: https://lore.kernel.org/lkml/20131006222342.GT19510@leaf/
>  
> +  **UNCOMMENTED_RGMII_MODE**
> +    Historially, the RGMII PHY modes specified in Device Trees have been
       ^^^^^^^^^^^
      	 Historically
> +    used inconsistently, often referring to the usage of delays on the PHY
> +    side rather than describing the board.
> +
> +    PHY modes "rgmii", "rgmii-rxid" and "rgmii-txid" modes require the clock
> +    signal to be delayed on the PCB; this unusual configuration should be
> +    described in a comment. If they are not (meaning that the delay is realized
> +    internally in the MAC or PHY), "rgmii-id" is the correct PHY mode.
>  
>  Commit message
>  --------------
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 784912f570e9d..57fcbd4b63ede 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -3735,6 +3735,17 @@ sub process {
>  			}
>  		}
>  
> +# Check for RGMII phy-mode with delay on PCB
> +		if ($realfile =~ /\.dtsi?$/ && $line =~ /^\+\s*(phy-mode|phy-connection-type)\s*=\s*"/ &&
> +		    !ctx_has_comment($first_line, $linenr)) {
> +			my $prop = $1;
> +			my $mode = get_quoted_string($line, $rawline);
> +			if ($mode =~ /^"rgmii(?:|-rxid|-txid)"$/) {
> +				CHK("UNCOMMENTED_RGMII_MODE",
> +				    "$prop $mode without comment -- delays on the PCB should be described, otherwise use \"rgmii-id\"\n" . $herecurr);
> +			}
> +		}
> +

My Perl-fu isn't good enough for me to review this properly... I think
though that Andrew mentioned something along the lines of 'Comment
should include PCB somewhere', but I don't know if this is easily
doable with checkpatch though.

Maxime