netdev - Re: [Intel-wired-lan] [PATCH iwl-net] idpf: cap maximum Rx buffer size

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Message-ID: <f839323a-4946-422b-a72a-c2efd71b2f42@intel.com>
Date: Mon, 3 Nov 2025 15:01:15 -0800
From: Jacob Keller <jacob.e.keller@...el.com>
To: Joshua Hay <joshua.a.hay@...el.com>, <intel-wired-lan@...ts.osuosl.org>
CC: <netdev@...r.kernel.org>, Alexander Lobakin
	<aleksander.lobakin@...el.com>, Madhu Chittim <madhu.chittim@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH iwl-net] idpf: cap maximum Rx buffer
 size



On 11/3/2025 1:20 PM, Joshua Hay wrote:
> The HW only supports a maximum Rx buffer size of 16K-128. On systems
> using large pages, the libeth logic can configure the buffer size to be
> larger than this. The upper bound is PAGE_SIZE while the lower bound is
> MTU rounded up to the nearest power of 2. For example, ARM systems with
> a 64K page size and an mtu of 9000 will set the Rx buffer size to 16K,
> which will cause the config Rx queues message to fail.
> 
> Initialize the bufq/fill queue buf_len field to the maximum supported
> size. This will trigger the libeth logic to cap the maximum Rx buffer
> size by reducing the upper bound.
> 
> Fixes: 74d1412ac8f37 ("idpf: use libeth Rx buffer management for payload buffer")
> Signed-off-by: Joshua Hay <joshua.a.hay@...el.com>
> Acked-by: Alexander Lobakin <aleksander.lobakin@...el.com>
> Reviewed-by: Madhu Chittim <madhu.chittim@...el.com>
> ---

Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>

>  drivers/net/ethernet/intel/idpf/idpf_txrx.c | 8 +++++---
>  drivers/net/ethernet/intel/idpf/idpf_txrx.h | 1 +
>  2 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/idpf/idpf_txrx.c b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> index 828f7c444d30..dcdd4fef1c7a 100644
> --- a/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> +++ b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> @@ -695,9 +695,10 @@ static int idpf_rx_buf_alloc_singleq(struct idpf_rx_queue *rxq)
>  static int idpf_rx_bufs_init_singleq(struct idpf_rx_queue *rxq)
>  {
>  	struct libeth_fq fq = {
> -		.count	= rxq->desc_count,
> -		.type	= LIBETH_FQE_MTU,
> -		.nid	= idpf_q_vector_to_mem(rxq->q_vector),
> +		.count		= rxq->desc_count,
> +		.type		= LIBETH_FQE_MTU,
> +		.buf_len	= IDPF_RX_MAX_BUF_SZ,
> +		.nid		= idpf_q_vector_to_mem(rxq->q_vector),
>  	};
>  	int ret;
>  
> @@ -754,6 +755,7 @@ static int idpf_rx_bufs_init(struct idpf_buf_queue *bufq,
>  		.truesize	= bufq->truesize,
>  		.count		= bufq->desc_count,
>  		.type		= type,
> +		.buf_len	= IDPF_RX_MAX_BUF_SZ,
>  		.hsplit		= idpf_queue_has(HSPLIT_EN, bufq),
>  		.xdp		= idpf_xdp_enabled(bufq->q_vector->vport),
>  		.nid		= idpf_q_vector_to_mem(bufq->q_vector),
> diff --git a/drivers/net/ethernet/intel/idpf/idpf_txrx.h b/drivers/net/ethernet/intel/idpf/idpf_txrx.h
> index 75b977094741..a1255099656f 100644
> --- a/drivers/net/ethernet/intel/idpf/idpf_txrx.h
> +++ b/drivers/net/ethernet/intel/idpf/idpf_txrx.h
> @@ -101,6 +101,7 @@ do {								\
>  		idx = 0;					\
>  } while (0)
>  
> +#define IDPF_RX_MAX_BUF_SZ			(16384 - 128)
>  #define IDPF_RX_BUF_STRIDE			32
>  #define IDPF_RX_BUF_POST_STRIDE			16
>  #define IDPF_LOW_WATERMARK			64



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