On Wed, Jun 10, 2026 at 04:43:15PM +0100, Matt Evans wrote:

The P2PDMA code currently provides two features under the same CONFIG_PCI_P2PDMA option:

1. Locate providers via pcim_p2pdma_provider()
2. Manage actual P2P DMA

Some drivers (such as vfio-pci) depend on 1, without having a hard dependency on 2.

A future commit expands the use of DMABUF in vfio-pci for non-P2P scenarios, relying on pcim_p2pdma_provider() always being present. If that depended on CONFIG_PCI_P2PDMA, it would make vfio-pci only available if CONFIG_ZONE_DEVICE is present (e.g. 64-bit systems), even when P2P is not needed.

To resolve this, introduce CONFIG_PCI_P2PDMA_CORE and refactor the basic provider functionality into a new p2pdma_core.c file. This is available even if the CONFIG_PCI_P2PDMA feature is disabled (or unavailable due to !CONFIG_ZONE_DEVICE). Then, drivers can enable any additional P2P features with the original CONFIG_PCI_P2PDMA (available when CONFIG_ZONE_DEVICE is set).

Signed-off-by: Matt Evans matt@ozlabs.org

MAINTAINERS | 2 +- drivers/pci/Kconfig | 10 ++-- drivers/pci/Makefile | 1 + drivers/pci/p2pdma.c | 109 ++-------------------------------- drivers/pci/p2pdma.h | 29 +++++++++ drivers/pci/p2pdma_core.c | 118 +++++++++++++++++++++++++++++++++++++ include/linux/pci-p2pdma.h | 24 ++++---- include/linux/pci.h | 2 +- 8 files changed, 174 insertions(+), 121 deletions(-) create mode 100644 drivers/pci/p2pdma.h create mode 100644 drivers/pci/p2pdma_core.c

diff --git a/MAINTAINERS b/MAINTAINERS index c2c6d79275c6..b21523b3bd8b 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -20617,7 +20617,7 @@ B: https://bugzilla.kernel.org C: irc://irc.oftc.net/linux-pci T: git git://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git F: Documentation/driver-api/pci/p2pdma.rst -F: drivers/pci/p2pdma.c +F: drivers/pci/p2pdma* F: include/linux/pci-p2pdma.h 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 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?

With the nit (and Bjorn's comments addressed) Reviewed-by: Pranjal Shrivastava praan@google.com

Thanks, Praan