Re: [v5,4/4] stmmac: s32: enable support for Multi-IRQ mode

[Simon Horman <horms@kernel.org>]

On Wed, Feb 25, 2026 at 11:02:42AM +0100, Jan Petrous wrote:
> On Wed, Feb 25, 2026 at 09:25:13AM +0000, Simon Horman wrote:
> > This is an AI-generated review of your patch. The human sending this
> > email has considered the AI review valid, or at least plausible.
> > 
> > For local reproduction steps see https://netdev-ai.bots.linux.dev/ai-local.html
> > ---
> > stmmac: s32: enable support for Multi-IRQ mode
> > 
> > This commit enables Multi-IRQ mode for the S32 DWMAC driver, allowing
> > per-queue IRQs for improved performance. The driver checks for multiple
> > queues and per-queue IRQs, enabling multi-IRQ mode when both are present.
> > 
> > > diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-s32.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-s32.c
> > > index af594a096676..4aad7077c9d6 100644
> > > --- a/drivers/net/ethernet/stmicro/stmmac/dwmac-s32.c
> > > +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-s32.c
> > 
> > [ ... ]
> > 
> > > @@ -165,6 +165,16 @@ static int s32_dwmac_probe(struct platform_device *pdev)
> > >  	plat->core_type = DWMAC_CORE_GMAC4;
> > >  	plat->pmt = 1;
> > >  	plat->flags |= STMMAC_FLAG_SPH_DISABLE;
> > > +
> > > +	/* Check for multi-IRQ config. Assumption: symmetrical rx/tx queues */
> > > +	if (plat->rx_queues_to_use > 1 &&
> > > +	    (res.rx_irq[0] > 0 && res.tx_irq[0] > 0)) {
> > > +		plat->flags |= STMMAC_FLAG_MULTI_MSI_EN;
> > > +		dev_info(dev, "Multi-IRQ mode (per queue IRQs) selected\n");
> > > +	} else {
> > > +		dev_info(dev, "MAC IRQ mode selected\n");
> > > +	}
> > 
> > Does this validation check all queues have IRQs? The condition verifies
> > only res.rx_irq[0] and res.tx_irq[0] but doesn't confirm that higher
> > queues have IRQs when rx_queues_to_use > 1.
> > 
> > If a device tree specifies multiple queues but only provides IRQs for
> > queue 0:
> > 
> >     snps,rx-queues-to-use = <2>;
> >     interrupt-names = "macirq", "rx-queue-0", "tx-queue-0";
> >                       /* queue 1 IRQs missing */
> > 
> > The driver would enable STMMAC_FLAG_MULTI_MSI_EN, but later in
> > stmmac_request_irq_multi_msi() (drivers/net/ethernet/stmicro/stmmac/
> > stmmac_main.c), queues with rx_irq[i] == 0 are silently skipped:
> > 
> >     for (i = 0; i < priv->plat->rx_queues_to_use; i++) {
> >         if (priv->rx_irq[i] <= 0)
> >             continue;  /* queue 1+ skipped, no handler registered */
> >         ...
> >     }
> > 
> > This would leave higher-numbered queues with no interrupt handler,
> > causing packet loss when traffic arrives on those queues.
> > 
> > Would it be safer to validate all queue IRQs before enabling multi-IRQ
> > mode, or fall back to MAC IRQ mode if any queue IRQ is missing?
> > 
> > > +
> > >  	plat->rx_fifo_size = 20480;
> > >  	plat->tx_fifo_size = 20480;
> 
> Hi Simon,
> 
> I already addressed this in v6 I sent today.

Thanks!