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

Mark Bloch
2026-02-27T08:16:23Z

On 27/02/2026 7:25, 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.
>

Thanks! I've looked at the patch, it seems fine and should fix the issue we
are seeing.

Mark

> Vivian "dramforever" Wang
>
> [1]: https://lore.kernel.org/all/20260220070239.1693303-1-nilay@linux.ibm.com/
>