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

[Robin Murphy]

On 2022-09-09 14:29, Christoph Hellwig wrote:
> 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.

Eh, it's behind CONFIG_EXPERT, which makes it enough of a "I think I 
know what I'm doing and accept responsibility for picking up the pieces 
if it breaks" thing.

Robin.