Re: [PATCH v4 1/4] PCI/MSI: Conservatively generalize no_64bit_msi into msi_addr_mask

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Feb 27, 2026 at 01:25:03PM +0800, Vivian Wang wrote:
> On 2/27/26 02:25, Mark Bloch wrote:
> > On 29/01/2026 3:56, Vivian Wang wrote:
> >> Some PCI devices have PCI_MSI_FLAGS_64BIT in the MSI capability, but
> >> implement less than 64 address bits. This breaks on platforms where such
> >> a device is assigned an MSI address higher than what's reachable.
> >>
> >> Currently, the no_64bit_msi bit is set for these devices, meaning that
> >> only 32-bit MSI addresses are allowed for them. However, on some
> >> platforms the MSI doorbell address is above the 32-bit limit but within
> >> the addressable range of the device.
> >>
> >> As a first step to enabling MSI on those combinations of devices and
> >> platforms, conservatively generalize the single-bit flag no_64bit_msi
> >> into msi_addr_mask. (The name msi_addr_mask is chosen to avoid confusion
> >> with msi_mask.)
> >>
> >> The translation is essentially:
> >>
> >> - no_64bit_msi = 1    ->    msi_addr_mask = DMA_BIT_MASK(32)
> >> - no_64bit_msi = 0    ->    msi_addr_mask = DMA_BIT_MASK(64)
> >> - if (no_64bit_msi)   ->    if (msi_addr_mask < DMA_BIT_MASK(64))
> >>
> > Hey Vivian,
> >
> > We are seeing issues while reloading mlx5 on a PPC64 platform.
> 
> Mea culpa. There's a fix on the list [1] since last Friday. I'm not sure
> why it hasn't moved yet, but please take a look.
> 
> [1]: https://lore.kernel.org/all/20260220070239.1693303-1-nilay@linux.ibm.com/

We needed testing on powerpc and sparc, which has now been done,
thanks to Han Gao (SPARC Enterprise T5220), Nathaniel Roach (SPARC
T5-2), and Venkat Rao Bagalkote (IBM Power System LPAR (pseries)).

It would be ideal to have acks from the powerpc and sparc maintainers,
so I just solicited those.

Thomas merged 386ced19e9a3 ("PCI/MSI: Convert the boolean no_64bit_msi
flag to a DMA address mask"), and could merge the fixes.  Otherwise I
can merge via PCI.

Bjorn