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[Qemu-devel] [RFC 0/4] AMBA platform device passthrough

From: Alvise Rigo
Subject: [Qemu-devel] [RFC 0/4] AMBA platform device passthrough
Date: Thu, 17 Apr 2014 19:29:31 +0200

These patches were born after trying the current work on device
passthrough (see thread "[Qemu-devel] [RFC v2 0/6] KVM platform device
passthrough") with a DMA330 and FastModels.  This work want to be the
starting point for dicussion on some aspects related to the next VFIO
platform development:

- [PATCH 1/4] Add a way to allocate memory region from a user pointer
  for devices, and not exclusively for RAM. This is useful to exclude
  the devices bound to VFIO from being DMA mapped by the VFIO memory

- [PATCH 2/4] Addition of the exec flag to the DMA mappings. This is
  mandatory only for the ARM SMMU: in its next version VFIO will be able
  to tell if the flag is supported.

- [PATCH 3/4] Possibility to bind a wider class of devices. In
  particular the patch proposes a solution to enhance a bit the device
  tree nodes generation, allowing to specify more than one compatibility
  property (handy for AMBA devices). This was required by the DMA330
  that needs “arm,pl330”,”arm,primecell” as compatibility string,
  together with a clock source defined in the device tree. In the future
  VFIO will be able to tell if we are dealing with an AMBA device; before
  that, we have to rely on the compatibility string to state that.

- [PATCH 4/4] Another approach to handle the EOI, starting from the
  assumption that we know in advance the location of the interrupt clear
  register of the device. Testing the reference patches I was noticing
  that the EOI mechanism was disabling the interrupt three times,
  because the kernel driver was reading some registers in the timer
  window before actually clearing the interrupt. This is of course
  another workaround and not the definitive solution until we can rely
  on a proper callback from the VGIC (something that we will see in a
  future version of VFIO for platform devices).

These patches are based on the QEMU branch mentioned in the original
thread ("[Qemu-devel] [RFC v2 0/6] KVM platform device passthrough").

Alvise Rigo (4):
  Allocate non-RAM MemoryRegion from user pointer
  Add EXEC_FLAG to VFIO DMA mappings
  Add AMBA devices support to VFIO
  MemoryRegion with EOI callbacks for VFIO Platform devices

 exec.c                     |   2 +-
 hw/arm/virt.c              |  39 +++++++++--
 hw/vfio/common.c           |   3 +
 hw/vfio/platform.c         | 158 ++++++++++++++++++++++++++++++++++++++++++---
 include/exec/memory.h      |  16 +++++
 linux-headers/linux/vfio.h |   1 +
 memory.c                   |  14 ++++
 memory_mapping.c           |   2 +-
 8 files changed, 220 insertions(+), 15 deletions(-)


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