We had a call with those interested and/or working on vfio
for platform devices.
Participants: Scott Wood, Varun Sethi, Bharat Bhushan, Peter Maydell,
Santosh Shukla, Alex Williamson, Alexander Graf,
Antonios Motakis, Christoffer Dall, Kim Phillips,
Stuart Yoder
Several aspects to vfio for platform devices:
1. IOMMU groups
-iommu driver needs to register a bus notifier for the platform bus
and create groups for relevant platform devices
-Antonios is looking at this for several ARM IOMMUs
-PAMU (Freescale) driver already does this
2. unbinding device from host
PCI:
echo 0000:06:0d.0 > /sys/bus/pci/devices/0000:06:0d.0/driver/unbind
Platform:
echo ffe101300.dma > /sys/bus/platform/devices/ffe101300.dma/driver/unbind
-don't believe there are issues or work to do here
3. binding device to vfio-platform driver
PCI:
echo 1102 0002 > /sys/bus/pci/drivers/vfio-pci/new_id
-this is probably the least understood issue-- platform drivers
register themselves with the bus for a specific "name"
string. That is matched with device tree "compatible" strings
later to bind a device to a driver
-we want is to have the vfio-platform driver to dynamically bind
to a variety of platform devices previously unknown to
vfio-platform
-ideally unbinding and binding could be an atomic operation
-Alex W pointed out that x86 could leverage this work so
keep that in mind in what we design
-Kim Phillips (Linaro) will start working on this
4. vfio kernel interface
-exposes regions and interrupts to user space via FDs
-there are 'info' ioctls that allow getting info about
regions/interrupts such as size and type of interrupt
-there is a proposed extension to the 'info' ioctls that
provides device tree paths, allowing user space to coorelate
resources with the device tree
(https://lists.cs.columbia.edu/pipermail/kvmarm/2013-July/006237.html)
5. QEMU
-some key tasks
-interacts with vfio kernel interface
-registers memslots
-needs to dynamically get device hooked up to VM's
platform bus, including IRQs
-needs to generate device tree node
-a key point: we don't believe that platform device passthru
in QEMU can be solved in a completely generic way. There will
need to be device specific code for each device type being passed
through...to do things like generate device tree nodes
-in general we expect a relatively small number of device types
to be passed through to VMs
-Alex Graf is working on dynamic creation of platform devices
for the PPC e500 paravirt machine
-see: http://lists.nongnu.org/archive/html/qemu-devel/2013-07/msg03614.html
-first step is dynamically generating a virtual UART
-that sets the stage to create and create vfio devices backed
by real hardware
There is a session at Linux Plumbers in a couple of weeks
and further discussions will happen there.
Regards,
Stuart
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