Subject: Re: [PATCH net] net: airoha: Add dma_rmb() and READ_ONCE() in airoha_qdma_rx_process()

From: Lorenzo Bianconi <[email-masked]>
Date: Fri, 3 Apr 2026 15:41:03 +0200

> Add missing dma_rmb() in airoha_qdma_rx_process routine to make sure the
> DMA read operations are completed when the NIC reports the processing on
> the current descriptor is done. Moreover, add missing READ_ONCE() in
> airoha_qdma_rx_process() for DMA descriptor control fields in order to
> avoid any compiler reordering.
> 
> Fixes: 23020f0493270 ("net: airoha: Introduce ethernet support for EN7581 SoC")
> Signed-off-by: Lorenzo Bianconi <[email-masked]>
> ---
>  drivers/net/ethernet/airoha/airoha_eth.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)

Please drop this version, I will post v2 to add a missing READ_ONCE() for
airoha_qdma_get_gdm_port().

Regards,
Lorenzo

> 
> diff --git a/drivers/net/ethernet/airoha/airoha_eth.c b/drivers/net/ethernet/airoha/airoha_eth.c
> index 95ba99b89428e4cafb91ff7813e43ffeb38e6d9b..29dea8b35f64bfdcf88bc09fd711e0d8b4f7b6fa 100644
> --- a/drivers/net/ethernet/airoha/airoha_eth.c
> +++ b/drivers/net/ethernet/airoha/airoha_eth.c
> @@ -612,15 +612,17 @@ static int airoha_qdma_rx_process(struct airoha_queue *q, int budget)
>  	while (done < budget) {
>  		struct airoha_queue_entry *e = &q->entry[q->tail];
>  		struct airoha_qdma_desc *desc = &q->desc[q->tail];
> -		u32 hash, reason, msg1 = le32_to_cpu(desc->msg1);
> -		struct page *page = virt_to_head_page(e->buf);
> -		u32 desc_ctrl = le32_to_cpu(desc->ctrl);
> +		u32 hash, reason, msg1, desc_ctrl;
>  		struct airoha_gdm_port *port;
>  		int data_len, len, p;
> +		struct page *page;
>  
> +		desc_ctrl = le32_to_cpu(READ_ONCE(desc->ctrl));
>  		if (!(desc_ctrl & QDMA_DESC_DONE_MASK))
>  			break;
>  
> +		dma_rmb();
> +
>  		q->tail = (q->tail + 1) % q->ndesc;
>  		q->queued--;
>  
> @@ -637,6 +639,7 @@ static int airoha_qdma_rx_process(struct airoha_queue *q, int budget)
>  		if (p < 0 || !eth->ports[p])
>  			goto free_frag;
>  
> +		page = virt_to_head_page(e->buf);
>  		port = eth->ports[p];
>  		if (!q->skb) { /* first buffer */
>  			q->skb = napi_build_skb(e->buf, q->buf_size);
> @@ -670,8 +673,8 @@ static int airoha_qdma_rx_process(struct airoha_queue *q, int budget)
>  			 * DMA descriptor. Report DSA tag to the DSA stack
>  			 * via skb dst info.
>  			 */
> -			u32 sptag = FIELD_GET(QDMA_ETH_RXMSG_SPTAG,
> -					      le32_to_cpu(desc->msg0));
> +			u32 msg0 = le32_to_cpu(READ_ONCE(desc->msg0));
> +			u32 sptag = FIELD_GET(QDMA_ETH_RXMSG_SPTAG, msg0);
>  
>  			if (sptag < ARRAY_SIZE(port->dsa_meta) &&
>  			    port->dsa_meta[sptag])
> @@ -679,6 +682,7 @@ static int airoha_qdma_rx_process(struct airoha_queue *q, int budget)
>  						  &port->dsa_meta[sptag]->dst);
>  		}
>  
> +		msg1 = le32_to_cpu(READ_ONCE(desc->msg1));
>  		hash = FIELD_GET(AIROHA_RXD4_FOE_ENTRY, msg1);
>  		if (hash != AIROHA_RXD4_FOE_ENTRY)
>  			skb_set_hash(q->skb, jhash_1word(hash, 0),
> 
> ---
> base-commit: ec7067e661193403a7a00980bda8612db5954142
> change-id: 20260402-airoha_qdma_rx_process-fix-reordering-722308255b65
> 
> Best regards,
> -- 
> Lorenzo Bianconi <[email-masked]>
>