Re: [PATCH v5 net-next 11/13] net: enetc: optimize the allocation of tx_bdr

[Vladimir Oltean <vladimir.oltean@nxp.com>]

On Thu, Oct 24, 2024 at 02:53:26PM +0800, Wei Fang wrote:
> From: Clark Wang <xiaoning.wang@nxp.com>
> 
> There is a situation where num_tx_rings cannot be divided by bdr_int_num.
> For example, num_tx_rings is 8 and bdr_int_num is 3. According to the
> previous logic, this results in two tx_bdr corresponding memories not
> being allocated, so when sending packets to tx ring 6 or 7, wild pointers
> will be accessed. Of course, this issue doesn't exist on LS1028A, because
> its num_tx_rings is 8, and bdr_int_num is either 1 or 2. However, there
> is a risk for the upcoming i.MX95. Therefore, it is necessary to ensure
> that each tx_bdr can be allocated to the corresponding memory.
> 
> Signed-off-by: Clark Wang <xiaoning.wang@nxp.com>
> Signed-off-by: Wei Fang <wei.fang@nxp.com>
> Reviewed-by: Claudiu Manoil <claudiu.manoil@nxp.com>
> Reviewed-by: Frank Li <Frank.Li@nxp.com>
> ---
> v5: no changes
> ---
>  drivers/net/ethernet/freescale/enetc/enetc.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
> index bd725561b8a2..bccbeb1f355c 100644
> --- a/drivers/net/ethernet/freescale/enetc/enetc.c
> +++ b/drivers/net/ethernet/freescale/enetc/enetc.c
> @@ -3049,10 +3049,10 @@ static void enetc_int_vector_destroy(struct enetc_ndev_priv *priv, int i)
>  int enetc_alloc_msix(struct enetc_ndev_priv *priv)
>  {
>  	struct pci_dev *pdev = priv->si->pdev;
> +	int v_tx_rings, v_remainder;
>  	int num_stack_tx_queues;
>  	int first_xdp_tx_ring;
>  	int i, n, err, nvec;
> -	int v_tx_rings;
>  
>  	nvec = ENETC_BDR_INT_BASE_IDX + priv->bdr_int_num;
>  	/* allocate MSIX for both messaging and Rx/Tx interrupts */
> @@ -3066,9 +3066,12 @@ int enetc_alloc_msix(struct enetc_ndev_priv *priv)
>  
>  	/* # of tx rings per int vector */
>  	v_tx_rings = priv->num_tx_rings / priv->bdr_int_num;
> +	v_remainder = priv->num_tx_rings % priv->bdr_int_num;
>  
>  	for (i = 0; i < priv->bdr_int_num; i++) {
> -		err = enetc_int_vector_init(priv, i, v_tx_rings);
> +		int num_tx_rings = i < v_remainder ? v_tx_rings + 1 : v_tx_rings;

It took me a moment to understand the mechanism through which this
works, even though I read the intention in the commit message.

Do you think this additional comment would help?

		/* Distribute the remaining TX rings to the first
		 * v_tx_rings interrupt vectors
		 */

> +
> +		err = enetc_int_vector_init(priv, i, num_tx_rings);
>  		if (err)
>  			goto fail;
>  	}
> -- 
> 2.34.1
>