Re: [PATCH net 8/8] net: bcmgenet: mask DMA_TIMEOUT_MASK when reading DMA_RING0_TIMEOUT

[Nicolai Buchwitz <nb@tipi-net.de>]

On 18.9.2026 02:07, Florian Fainelli wrote:
> bcmgenet_get_coalesce() reads DMA_RING0_TIMEOUT to calculate
> rx_coalesce_usecs without masking out bits outside DMA_TIMEOUT_MASK
> (16 bits). If upper bits are non-zero or contain status/flags, the
> computed value of rx_coalesce_usecs returned to userspace via ethtool
> becomes corrupted.
> 
> Mask the register read with DMA_TIMEOUT_MASK before computing the
> timeout in microseconds.
> 
> Fixes: 4a29645bfe6c ("net: bcmgenet: Implement RX coalescing control 
> knobs")
> Assisted-by: LLM
> Co-authored-by: Cursor <cursoragent@cursor.com>
> Change-Id: I4c5b5019e764dbd0c7e51bd8c7365939a4736e44
> ---
>  drivers/net/ethernet/broadcom/genet/bcmgenet.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c 
> b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> index 3a6a2f075959..b15e64a484b4 100644
> --- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> +++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> @@ -852,7 +852,8 @@ static int bcmgenet_get_coalesce(struct net_device 
> *dev,
>  	ec->rx_max_coalesced_frames =
>  		bcmgenet_rdma_ring_readl(priv, 0, DMA_MBUF_DONE_THRESH);
>  	ec->rx_coalesce_usecs =
> -		bcmgenet_rdma_readl(priv, DMA_RING0_TIMEOUT) * 8192 / 1000;
> +		(bcmgenet_rdma_readl(priv, DMA_RING0_TIMEOUT) &
> +		 DMA_TIMEOUT_MASK) * 8192 / 1000;
> 
>  	for (i = 0; i <= priv->hw_params->rx_queues; i++) {
>  		ring = &priv->rx_rings[i];

Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>

Thanks,
Nicolai