Hi Logan,
On 02/07/2026 16:45, Logan Gunthorpe wrote:
On 2026-07-01 11:12 a.m., Matt Evans wrote:>
PCI POWER CONTROL diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig index 33c88432b728..59d70bc84cc9 100644 --- a/drivers/pci/Kconfig +++ b/drivers/pci/Kconfig @@ -206,11 +206,7 @@ config PCIE_TPH config PCI_P2PDMA bool "PCI peer-to-peer transfer support" depends on ZONE_DEVICE
- #
- # The need for the scatterlist DMA bus address flag means PCI P2PDMA
- # requires 64bit
- #
- depends on 64BIT
- select PCI_P2PDMA_CORE
Can we remove this dependency on 64BIT? Althogh it looks like af2880ec440 complicated the issue a bit.
If I remember correctly, the original reason for this is because on 64bit systems dma_flags fit into unusued space in struct scatterlist and on 32bit systems this space didn't exist and thus adding the flag required increasing the size of the structure which wasn't desirable at the time.
But af2880ec440 introduced CONFIG_NEED_SG_DMA_FLAGS which doesn't depend on 64bit which means if CONFIG_IOMMU_DMA and CONFIG_SWIOTLB are now set on 32bit systems that structure will grow quite a bit.
There was some discussion on this aspect of af2880ec440 in the corresponding v3 patch, for example:
https://lore.kernel.org/all/feaefa41-9f67-4d4f-a3e0-282dca41f3eb@ozlabs.org/
It seems CONFIG_NEED_SG_DMA_FLAGS doesn't have a hard/functional dependency on 64BIT (and it can be enabled on some !64BIT configs already, despite what the stale comments say).
So maybe at this point it's fine to enable this on 32bit systems and we can remove this requirement. However, I think we should do that explicitly in its own patch, not hide it in this refactoring patch.
Your question does prove it's too stealthy as-is. :) PCI_P2PDMA still can't be enabled on 32-bit systems because of its ZONE_DEVICE -> MEMORY_HOTPLUG -> 64BIT dependency. So we're not enabling 32-bit support for PCI_P2PDMA here, but it's not obvious and so I'll re-add the `depends on 64BIT`. At least then it won't be enabled without intention if someone enables ZONE_DEVICE on 32-bit systems...
Thanks,
Matt