Re: [PATCH net-next] net: stmmac: enable RPS and RBU interrupts

Sam Edwards
2026-04-13T01:42:17Z

On Sun, Apr 12, 2026 at 7:23 AM Russell King (Oracle)
<linux@armlinux.org.uk> wrote:
> As the dwmac 5.0 core receive path seems to lock up after the first
> RBU, I never see more than one of those at a time.
>
> Right now, I consider this pretty much unsolvable - I've spent quite
> some time looking at it and trying various approaches, nothing seems
> to fix it. However, adding dma_rmb() in the descriptor cleanup/refill
> paths does seem to improve the situation a little with the 480Mbps
> case, because I think it means that we're reading the descriptors in
> a more timely manner after the hardware has updated them.

Hey Russell,

I'd like to repro this but I currently can't boot net-next. My issue
is the same as [1], and the patch to fix it [2] isn't yet committed
anywhere apparently.

This prevents my Jetson Xavier NX from starting at all (and after
enough attempts, corrupts eMMC); I'm surprised you're not suffering
the same effects. But because this bug lives in the IOMMU subsystem
(and it has somewhat inconsistent effects), perhaps this is just a
different way it manifests? Could you confirm whether your dwmac hang
happens with IOMMU disabled, and/or with [1] reverted or [2] applied?

I'm using a defconfig build and a fairly minimal cmdline (just
console=, root=, and rootwait).

Cheers,
Sam

[1] https://lore.kernel.org/all/8800a38b-8515-4bbe-af15-0dae81274bf7@nvidia.com/
[2] https://lore.kernel.org/all/0-v1-664d3acaabb9+78b-iommu_gather_always_jgg@nvidia.com/