linux-kernel - Re: [RFC net-next 04/15] net: cpc: add protocol header structure and API

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Message-ID: <0c7a753b-cdc6-4036-84af-909ca1df3f3a@lunn.ch>
Date: Mon, 12 May 2025 04:41:05 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Damien Riégel <damien.riegel@...abs.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>,
	Silicon Labs Kernel Team <linux-devel@...abs.com>,
	netdev@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC net-next 04/15] net: cpc: add protocol header structure and
 API

> +struct cpc_header {
> +	u8 ctrl;
> +	u8 ep_id;
> +	u8 recv_wnd;
> +	u8 seq;
> +	u8 ack;
> +	union {
> +		u8 extension[3];
> +		struct __packed {
> +			__le16 mtu;
> +			u8 reserved;
> +		} syn;
> +		struct __packed {
> +			__le16 payload_len;
> +			u8 reserved;

These two le16 are unaligned for no good reason. Put the reserved byte
first, then the u16. Once you have done that, you might be able to
throw away all the __packed because it is then all naturally aligned.

	Andrew