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Date: Fri, 24 Jul 2026 16:48:58 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Luke Howard <lukeh@padl.com>
Cc: Vladimir Oltean <olteanv@gmail.com>, "David S. Miller"
 <davem@davemloft.net>, Eric Dumazet <edumazet@google.com>, Paolo Abeni
 <pabeni@redhat.com>, Vivien Didelot <vivien.didelot@gmail.com>, Gregory
 CLEMENT <gregory.clement@bootlin.com>, Andrew Lunn <andrew@lunn.ch>,
 Richard Cochran <richardcochran@gmail.com>, Cedric Jehasse
 <cedric.jehasse@gmail.com>, Kieran Tyrrell <kieran@sienda.com>, Max
 Holtmann <mh@rme-audio.de>, Max Hunter <max@huntershome.org>, Christoph
 Mellauner <christoph.mellauner@joyned.at>, Simon Gapp
 <simon.gapp@gapp-audio.com>, netdev@vger.kernel.org,
 linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next v3 2/3] net: dsa: mv88e6xxx: embedded PTP
 timestamp support
Message-ID: <20260724164858.4581408e@kernel.org>
In-Reply-To: <20260719-mv88e6xxx-ptp-fixes-v3-2-161386ac8a62@padl.com>
References: <20260719-mv88e6xxx-ptp-fixes-v3-0-161386ac8a62@padl.com>
	<20260719-mv88e6xxx-ptp-fixes-v3-2-161386ac8a62@padl.com>
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On Sun, 19 Jul 2026 15:30:54 +1000 Luke Howard wrote:
> +	/* APPEND means the switch appended the time stamp as a 4-byte trailer
> +	 * (not all switches support this). Any other non-zero value is the byte
> +	 * offset past the start of the PTP common header at which the switch
> +	 * overwrote the time stamp in place (e.g. the reserved header bytes).
> +	 */
> +	if (arr_ts_mode == MV88E6XXX_PTP_ARR_TS_MODE_APPEND && skb->len >= 4) {
> +		if (skb_linearize(skb))
> +			return false;
> +
> +		*ns = (u64)get_unaligned_be32(skb_tail_pointer(skb) - 4);
> +		if (pskb_trim_rcsum(skb, skb->len - 4))
> +			return false;

The append mode would extend the frame, and possibly run afoul the MTU
on the conduit AFAIU? Since neither implemented chip uses this it's
both dead code and questionable. Let's remove it.