Re: [PATCH net-next] net: stmmac: dwxgmac2: configure INTM for per-channel interrupt routing

[Jakub Kicinski <kuba@kernel.org>]

On Tue, 28 Jul 2026 11:43:03 +0800 Zxyan Zhu wrote:
> The commit message does a poor job of explaining the actual impact,
> so let me clarify.
> 
> I've verified on hardware with XGMAC and multi-MSI enabled. The
> results are definitive:
> 
>   INTM=00 (default):
>     - 5.4 million interrupts on the common IRQ line in 3 seconds
>     - ~1.8 million IRQ_NONE returns per second
> 
>   INTM=01:
>     - 0 interrupts on the common IRQ line
>     - Per-channel IRQs work normally
>     - 10G line rate works correctly
> 
> The behavior is that with INTM=00, sbd_intr_o is also asserted for
> each DMA completion event. The common IRQ handler
> stmmac_mac_interrupt() only processes MAC-layer events (LPI, PMT,
> timestamps) and returns IRQ_NONE for DMA completion events, causing
> the interrupt storm. With INTM=01, sbd_intr_o is not asserted for
> DMA transfer completion events, which is the correct mode for
> per-channel interrupt routing.

Got it, could you respin with this clarification in the commit message?

> Regarding net vs net-next: XGMAC multi-MSI has never worked correctly
> since it was introduced, so this is not a regression. The same
> INTM=1 configuration for GMAC4 was merged via net-next (6ccf12ae111e
> "net: stmmac: use interrupt mode INTM=1 for multi-MSI"). I'm leaning
> toward net-next for consistency, but since this makes multi-MSI
> completely non-functional without it, I'd appreciate your opinion on
> whether net is more appropriate.

Makes sense, we can stick to net-next. Please also add a note to the
commit msg that "XGMAC multi-MSI has never worked correctly."
It will help backporting. Thanks!