Re: [PATCH v2 08/14] greybus: cpc: add and validate sequence numbers

["Jérôme Pouiller" <jerome.pouiller@silabs.com>]

On Thursday 15 January 2026 16:58:01 Central European Standard Time Damien Riégel wrote:
> The first step in making the CPC header actually do something is to add
> the sequence number to outgoing messages and validate that incoming
> frames are received in order.
> 
> At this stage, the driver doesn't send standalone acks, so if a message
> with Sequence X is received, the remote will not be acknowledged until a
> message targeting that CPort comes from the Greybus layer. Only then the
> driver will ack with acknowledgedment number of X + 1.
> 
> Signed-off-by: Damien Riégel <damien.riegel@silabs.com>
> ---
> Changes in v2:
>   - change dev_warn to ratelimited version in cpc_protocol_on_data
> 
>  drivers/greybus/cpc/Makefile   |  2 +-
>  drivers/greybus/cpc/cpc.h      | 20 +++++++++++++++
>  drivers/greybus/cpc/cport.c    | 25 ++++++++++++++++++
>  drivers/greybus/cpc/header.c   | 17 ++++++++++++
>  drivers/greybus/cpc/header.h   |  2 ++
>  drivers/greybus/cpc/host.c     | 13 +++++++---
>  drivers/greybus/cpc/protocol.c | 47 ++++++++++++++++++++++++++++++++++
>  7 files changed, 121 insertions(+), 5 deletions(-)
>  create mode 100644 drivers/greybus/cpc/header.c
>  create mode 100644 drivers/greybus/cpc/protocol.c
> 
[...]
> diff --git a/drivers/greybus/cpc/protocol.c b/drivers/greybus/cpc/protocol.c
> new file mode 100644
> index 00000000000..ff65757b40f
> --- /dev/null
> +++ b/drivers/greybus/cpc/protocol.c
> @@ -0,0 +1,47 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2025, Silicon Laboratories, Inc.
> + */
> +
> +#include <linux/skbuff.h>
> +
> +#include "cpc.h"
> +#include "header.h"
> +#include "host.h"
> +
> +void cpc_protocol_prepare_header(struct sk_buff *skb, u8 ack)
> +{
> +	struct cpc_header *hdr;
> +
> +	skb_push(skb, sizeof(*hdr));
> +
> +	hdr = (struct cpc_header *)skb->data;
> +	hdr->ack = ack;
> +	hdr->recv_wnd = 0;
> +	hdr->ctrl_flags = 0;
> +	hdr->seq = CPC_SKB_CB(skb)->seq;

I suggest "memset(hdr, 0, sizeof(*hdr))", so there is no doubts all the
members are set.

[...]

-- 
Jérôme Pouiller