[PATCH net-next] net: stmmac: fpe: Keep pmac always enabled

[Maxime Chevallier]

Hi,

On 7/27/26 07:13, muhammad.nazim.amirul.nazle.asmade at altera.com wrote:
> From: Nazim Amirul <muhammad.nazim.amirul.nazle.asmade at altera.com>
> 
> The preemptive MAC in DWMAC is always enabled, meaning DWMAC is always
> ready to receive preemptive mPackets. Keep pmac_enabled true at init
> time and reject attempts to disable it via ethtool set_mm.
> 
> The FPE residual queue (fprq) controls which Rx queue receives residual
> preemptive mPackets from the pmac. Move its configuration from
> stmmac_fpe_configure_tx() to stmmac_fpe_configure_pmac() where it
> logically belongs.
> 
> Also add a missing return in stmmac_fpe_init() so that the pmac_enabled
> initialization is not reached on hardware where FPE is not supported by
> the driver.

Can you split this up into individual patches, one for the stmmac_set_mm() and
stmmac_fpe_init() to validate that we keep pmac on, one for the missing return,
and one for the pmac configuration in the right fonction ?

Also one comment bellow :> 
> Signed-off-by: Rohan G Thomas <rohan.g.thomas at altera.com>
> Signed-off-by: Nazim Amirul <muhammad.nazim.amirul.nazle.asmade at altera.com>
> ---
>  .../ethernet/stmicro/stmmac/stmmac_ethtool.c  |  7 ++++
>  .../net/ethernet/stmicro/stmmac/stmmac_fpe.c  | 34 ++++++++++++-------
>  2 files changed, 29 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
> index 92585d27ab88..8ebdd249e5c8 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
> @@ -1064,6 +1064,13 @@ static int stmmac_set_mm(struct net_device *ndev, struct ethtool_mm_cfg *cfg,
>  	if (err)
>  		return err;
>  
> +	if (!priv->dma_cap.fpesel)
> +		return -EOPNOTSUPP;
> +
> +	/* DWMAC always have preemptible MAC enabled */
> +	if (!cfg->pmac_enabled)
> +		return -EINVAL;
> +
>  	stmmac_fpe_set_add_frag_size(priv, frag_size);
>  	ethtool_mmsv_set_mm(&priv->fpe_cfg.mmsv, cfg);
>  
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_fpe.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_fpe.c
> index c54c70224351..2bfa84ad04a6 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_fpe.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_fpe.c
> @@ -47,20 +47,13 @@ static void stmmac_fpe_configure_tx(struct ethtool_mmsv *mmsv, bool tx_enable)
>  	struct stmmac_fpe_cfg *cfg = container_of(mmsv, struct stmmac_fpe_cfg, mmsv);
>  	struct stmmac_priv *priv = container_of(cfg, struct stmmac_priv, fpe_cfg);
>  	const struct stmmac_fpe_reg *reg = cfg->reg;
> -	u32 num_rxq = priv->plat->rx_queues_to_use;
>  	void __iomem *ioaddr = priv->ioaddr;
> -	u32 value;
>  
> -	if (tx_enable) {
> +	if (tx_enable)
>  		cfg->fpe_csr = STMMAC_MAC_FPE_CTRL_STS_EFPE;
> -		value = readl(ioaddr + reg->rxq_ctrl1_reg);
> -		value &= ~reg->fprq_mask;
> -		/* Keep this SHIFT, FIELD_PREP() expects a constant mask :-/ */
> -		value |= (num_rxq - 1) << __ffs(reg->fprq_mask);
> -		writel(value, ioaddr + reg->rxq_ctrl1_reg);
> -	} else {
> +	else
>  		cfg->fpe_csr = 0;
> -	}
> +
>  	writel(cfg->fpe_csr, ioaddr + reg->mac_fpe_reg);
>  }
>  
> @@ -68,10 +61,11 @@ static void stmmac_fpe_configure_pmac(struct ethtool_mmsv *mmsv, bool pmac_enabl
>  {
>  	struct stmmac_fpe_cfg *cfg = container_of(mmsv, struct stmmac_fpe_cfg, mmsv);
>  	struct stmmac_priv *priv = container_of(cfg, struct stmmac_priv, fpe_cfg);
> +	u32 num_rxq = priv->plat->rx_queues_to_use;
>  	const struct stmmac_fpe_reg *reg = cfg->reg;
>  	void __iomem *ioaddr = priv->ioaddr;
>  	unsigned long flags;
> -	u32 value;
> +	u32 value, value_2;
>  
>  	spin_lock_irqsave(&priv->hw->irq_ctrl_lock, flags);
>  	value = readl(ioaddr + reg->int_en_reg);
> @@ -83,6 +77,14 @@ static void stmmac_fpe_configure_pmac(struct ethtool_mmsv *mmsv, bool pmac_enabl
>  
>  			value |= reg->int_en_bit;
>  		}
> +		/* Frame Preemption Residue Queue is the Rx Queue to which
> +		 * residual preemptive mPackets must be forwarded from the pmac.
> +		 */
> +		value_2 = readl(ioaddr + reg->rxq_ctrl1_reg);
> +		value_2 &= ~reg->fprq_mask;
> +		/* Keep this SHIFT, FIELD_PREP() expects a constant mask :-/ */

you can use u32_replace_bits for non constant expr :

https://elixir.bootlin.com/linux/v7.2-rc4/source/include/linux/bitfield.h#L236

(it's autogenerated and not documented, hence very hard to find IMO)

Maxime