Heya Robin, On 23/06/2026 16:48, Robin Murphy wrote: > On 12/06/2026 3:31 pm, Matt Evans wrote: >> Hi Kevin, Pranjal, (+Robin, hi!) > > Oh hey there! :) > >> On 12/06/2026 04:39, Tian, Kevin wrote: >>>> From: Pranjal Shrivastava <[email protected]> >>>> Sent: Friday, June 12, 2026 2:38 AM >>>> >>>> On Wed, Jun 10, 2026 at 04:43:15PM +0100, Matt Evans wrote: >>>>> --- 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 >>>>> select GENERIC_ALLOCATOR >>>>> select NEED_SG_DMA_FLAGS >>>>> help >>>> >>>> Nit: Did we drop depends on 64BIT intentionally here? I guess the full >>>> PCI_P2PDMA stack still selects NEED_SG_DMA_FLAGS? IIRC, >>>> NEED_SG_DMA_FLAGS doesn't select 64BIT? >>> >>> seems that comment is stale. According to the commit msg: >>> >>> " it would make vfio-pci only available if CONFIG_ZONE_DEVICE is >>> present (e.g. 64-bit systems), " >>> >>> so it sounds a redundant dependency hence is removed. >> >> This was intentional. In practice there is still a dependency on 64BIT >> for PCI_P2PDMA, but it is because of ZONE_DEVICE (and mem hotplug). The >> key need is PCI_P2PDMA_CORE is available on !64BIT for VFIO, but I >> didn't see a requirement from PCI_P2PDMA itself (as opposed to its >> dependencies). If I've missed one, I can put it back... >> >> But NEED_SG_DMA_FLAGS doesn't smell quite right; I see from comments in >> >> af2880ec44021 ("scatterlist: add dedicated config for DMA flags") >> >> that it assumes 64BIT, but it seems to be missing a "depends on 64BIT". >> >> Robin -- should that depend on 64BIT? > > Indeed, looking at the history it seems like that was overlooked, but it > worked out at the time since the only selector of NEED_SG_DMA_FLAGS was > PCI_P2PDMA as you say. If we're now generalising then moving the > explicit 64BIT dependency to NEED_SG_DMA_FLAGS itself sounds like the > right thing to do.
Cheers for confirming. I'll send a patch separate to this series (since the deps work out OK for PCI_P2PDMA for the reasons mentioned). Ta, Matt
