Re: [PATCH net 6/6] iavf: cap advertised max_pkt_size at the single-buffer HW limit

[Alexander Lobakin <aleksander.lobakin@intel.com>]

From: Anthony Nguyen <anthony.l.nguyen@intel.com>
Date: Mon, 28 Sep 2026 16:04:27 -0700

> From: Dave Butler <david.butler@appgate.com>
> 
> Since commit 5fa4caff59f2 ("iavf: switch to Page Pool")
> iavf_configure_queues() advertises max_pkt_size to the PF as:
> 
> 	max_frame = LIBIE_MAX_RX_FRM_LEN(adapter->rx_rings->pp->p.offset);
> 	max_frame = min_not_zero(adapter->vf_res->max_mtu, max_frame);
> 
> LIBIE_MAX_RX_FRM_LEN (16382) is the multi-descriptor scatter/gather frame
> ceiling, not a single-queue value, and it exceeds the E810 MAC frame size
> maximum of 9728. Per the E810 datasheet (613875-009 section 13.2.2.17.1)
> the Tx frame-size register PRTDCB_TDPUC.MAX_TXFRAME has a maximum of
> 0x2600 (9728); larger frames are discarded. The in-tree ice driver encodes
> the same value as ICE_AQ_SET_MAC_FRAME_SIZE_MAX (== LIBIE_MAX_RX_BUF_LEN ==
> 9728), and the VF clamped max_frame to IAVF_MAX_RXBUFFER (9728) before this
> commit.

[...]

> diff --git a/drivers/net/ethernet/intel/iavf/iavf_virtchnl.c b/drivers/net/ethernet/intel/iavf/iavf_virtchnl.c
> index ec234cc8bd9d..680a28a739bf 100644
> --- a/drivers/net/ethernet/intel/iavf/iavf_virtchnl.c
> +++ b/drivers/net/ethernet/intel/iavf/iavf_virtchnl.c
> @@ -382,6 +382,14 @@ void iavf_configure_queues(struct iavf_adapter *adapter)
>  
>  	max_frame = LIBIE_MAX_RX_FRM_LEN(adapter->rx_rings->pp->p.offset);
>  	max_frame = min_not_zero(adapter->vf_res->max_mtu, max_frame);
> +	/* The PF programs max_pkt_size into the per-queue Rx context "rxmax".
> +	 * LIBIE_MAX_RX_FRM_LEN is the multi-descriptor (S/G) frame ceiling
> +	 * (16382), but that exceeds the E810 max MAC frame size (9728); some
> +	 * PFs reject the out-of-range value with VIRTCHNL_STATUS_ERR_PARAM.
> +	 * Cap it at the single-buffer HW limit (== the MAC frame max),
> +	 * restoring the pre-Page-Pool behaviour.
> +	 */
> +	max_frame = min(max_frame, LIBIE_MAX_RX_BUF_LEN);

Shouldn't we cap it to 9728 instead?>
>  	if (adapter->current_op != VIRTCHNL_OP_UNKNOWN) {
>  		/* bail because we already have a command pending */

Thanks,
Olek