Re: [PATCH] PCI: dwc: ep: Fix regression in dw_pcie_ep_raise_msi_irq()

[Niklas Cassel <cassel@kernel.org>]

On Tue, Feb 10, 2026 at 09:22:58PM +0100, Niklas Cassel wrote:
> What commit 8719c64e76bf ("PCI: dwc: ep: Cache MSI outbound iATU mapping")
> did was to map it once on startup, that way we don't re-program the outbound
> iATU on every pci_epc_raise_irq() call. Before this commit, every
> pci_epc_raise_irq() call could potentially cause ongoing outbound transactions
> to be sent untranslated. Often the transactions that were sent untranslated
> did not appear to be the MSI writel() itself, but other transactions performed
> by the eDMA.

I guess it could have been the MSI writel() too.

Perhaps another fix could have been to just do a readl() after the writel(),
before the unmap().

If that is preferred, should be simple to test, since the bug is very easy
to reproduce, just run nvmet-pci-epf and do some transfers with a high queue
depth and see the IOMMU errors on the host.

I do like the solution that caches the MSI address though, as that avoids
the extra latency of a map() + unmap() for every pci_epc_raise_irq() call.


Kind regards,
Niklas