Re: [PATCH iwl-next v7 5/9] igc: Add support for frame preemption verification

[Vladimir Oltean]

On Mon, Mar 03, 2025 at 05:26:54AM -0500, Faizal Rahim wrote:
> +static inline bool igc_fpe_is_verify_or_response(union igc_adv_rx_desc *rx_desc,
> +						 unsigned int size)
> +{
> +	u32 status_error = le32_to_cpu(rx_desc->wb.upper.status_error);
> +	int smd;
> +
> +	smd = FIELD_GET(IGC_RXDADV_STAT_SMD_TYPE_MASK, status_error);
> +
> +	return (smd == IGC_RXD_STAT_SMD_TYPE_V || smd == IGC_RXD_STAT_SMD_TYPE_R) &&
> +		size == SMD_FRAME_SIZE;
> +}

The NIC should explicitly not respond to frames which have an SMD-V but
are not "verify" mPackets (7 octets of 0x55 + 1 octet SMD-V + 60 octets
of 0x00 + mCRC - as per 802.3 definitions). Similarly, it should only
treat SMD-R frames which contain 7 octets of 0x55 + 1 octet SMD-R + 60
octets of 0x00 + mCRC as "respond" mPackets, and only advance its
verification state machine based on those.

Specifically, it doesn't look like you are ensuring the packet payload
contains 60 octets of zeroes. Is this something that the hardware
already does for you, or is it something that needs further validation
and differentiation in software?