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 praan@google.com 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, Robin.
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 praan@google.com 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
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Matt Evans -
Robin Murphy