Re: [PATCH v4 2/9] ptp: Add generic ptp message type function

[Russell King - ARM Linux admin <linux@armlinux.org.uk>]

On Tue, Aug 18, 2020 at 12:32:44PM +0200, Kurt Kanzenbach wrote:
> The message type is located at different offsets within the ptp header depending
> on the ptp version (v1 or v2). Therefore, drivers which also deal with ptp v1
> have some code for it.
> 
> Extract this into a helper function for drivers to be used.
> 
> Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
> Reviewed-by: Richard Cochran <richardcochran@gmail.com>
> Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
> ---
>  include/linux/ptp_classify.h | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/include/linux/ptp_classify.h b/include/linux/ptp_classify.h
> index 996f31e8f35d..39bad015d1d6 100644
> --- a/include/linux/ptp_classify.h
> +++ b/include/linux/ptp_classify.h
> @@ -96,6 +96,31 @@ unsigned int ptp_classify_raw(const struct sk_buff *skb);
>   */
>  struct ptp_header *ptp_parse_header(struct sk_buff *skb, unsigned int type);
>  
> +/**
> + * ptp_get_msgtype - Extract ptp message type from given header
> + * @hdr: ptp header
> + * @type: type of the packet (see ptp_classify_raw())
> + *
> + * This function returns the message type for a given ptp header. It takes care
> + * of the different ptp header versions (v1 or v2).
> + *
> + * Return: The message type
> + */
> +static inline u8 ptp_get_msgtype(const struct ptp_header *hdr,
> +				 unsigned int type)
> +{
> +	u8 msgtype;
> +
> +	if (unlikely(type & PTP_CLASS_V1)) {
> +		/* msg type is located at the control field for ptp v1 */
> +		msgtype = hdr->control;
> +	} else {
> +		msgtype = hdr->tsmt & 0x0f;
> +	}
> +
> +	return msgtype;
> +}

Are there 256 different message types in V1? I wonder how hardware
that uses the message type as an index into a 16-bit lookup table
and supports both V1 and V2 cope with that (such as the Marvell PTP
implementation found in their DSA switches and PHYs.)

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