[PATCH net] net: stmmac: Don't set or get RSS parameters when not supported

[Jitendra Vegiraju]

Hi Maxime,
On Sat, Sep 26, 2026 at 2:34 AM Maxime Chevallier
<maxime.chevallier at bootlin.com> wrote:
>
> The RSS kselftests fail on stmmac, and this is partly due to the driver
> reporting bogus data for the RSS ops :
>
>  - ethtool -x reports an indirection table and a key while the hardware
>    doesn't have any of that
>  - ethtool -X fails with -EINVAL.
>
> Let's return early in the rss ops if we know the hardware and platform
> don't support RSS.
>
> Note that RSS is currently not supported on any devices upstream, so
> code that was already useless is now effectively dead. It has been the
> case since 2019 when the code was added, as platforms need to set rss_en
> in their plat data, and no glue ever did that.
>
> Russell King ran a poll in february 2026 [1] asking if the code should
> be dropped, without any reply going in either direction.
>
> Jitendra Vegiraju from Broadcom sent 9 iterations of a Broadcom PCIe glue
> driver [2] that actually sets rss_en = 1, so there's some hope that this
> may be used in the future.

>
> [1] : https://lore.kernel.org/netdev/aYd4BkAeNW6d0iIC@shell.armlinux.org.uk/
> [2] : https://lore.kernel.org/netdev/20260402213629.1996133-1-jitendra.vegiraju@broadcom.com/
>
> Fixes: 76067459c686 ("net: stmmac: Implement RSS and enable it in XGMAC core")
> Signed-off-by: Maxime Chevallier <maxime.chevallier at bootlin.com>
> ---
> Jitendra, do you have plans to continue iterating on the BCM8958x glue ?

Yes, we plan to resubmit the BCM8958x glue driver patches.
We paused it for a while. But, we are planning to test with the latest
net-next and submit the patches again.
Thanks,
Jitendra
>
> Thanks,
>
> Maxime
>
>  drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
> index 1be5310ca766..4e917a448271 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
> @@ -927,6 +927,9 @@ static u32 stmmac_get_rxfh_key_size(struct net_device *dev)
>  {
>         struct stmmac_priv *priv = netdev_priv(dev);
>
> +       if (!priv->dma_cap.rssen || !priv->plat->rss_en)
> +               return 0;
> +
>         return sizeof(priv->rss.key);
>  }
>
> @@ -934,6 +937,9 @@ static u32 stmmac_get_rxfh_indir_size(struct net_device *dev)
>  {
>         struct stmmac_priv *priv = netdev_priv(dev);
>
> +       if (!priv->dma_cap.rssen || !priv->plat->rss_en)
> +               return 0;
> +
>         return ARRAY_SIZE(priv->rss.table);
>  }
>
> @@ -943,6 +949,9 @@ static int stmmac_get_rxfh(struct net_device *dev,
>         struct stmmac_priv *priv = netdev_priv(dev);
>         int i;
>
> +       if (!priv->dma_cap.rssen || !priv->plat->rss_en)
> +               return -EOPNOTSUPP;
> +
>         if (rxfh->indir) {
>                 for (i = 0; i < ARRAY_SIZE(priv->rss.table); i++)
>                         rxfh->indir[i] = priv->rss.table[i];
> @@ -962,6 +971,9 @@ static int stmmac_set_rxfh(struct net_device *dev,
>         struct stmmac_priv *priv = netdev_priv(dev);
>         int i;
>
> +       if (!priv->dma_cap.rssen || !priv->plat->rss_en)
> +               return -EOPNOTSUPP;
> +
>         if (rxfh->hfunc != ETH_RSS_HASH_NO_CHANGE &&
>             rxfh->hfunc != ETH_RSS_HASH_TOP)
>                 return -EOPNOTSUPP;
> --
> 2.55.0
>
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