Re: [PATCH v5 2/2] PCI: dwc: Add support for 64-bit MSI target address

[Christoph Hellwig]

On Thu, Aug 25, 2022 at 06:50:25PM +0000, Will McVicker wrote:
> Since not all devices require a 32-bit MSI address, add support to the
> PCIe host driver to allow setting the DMA mask to 64-bits if the 32-bit
> allocation fails. This allows kernels to disable ZONE_DMA32 and bounce
> buffering (swiotlb) without risking not being able to get a 32-bit address
> during DMA allocation.

Umm.  You can't just disable ZONE_DMA32.  Linux absolutely requires a
32-bit dma mask to work, it is in fact the implicit default.