Re: [Qemu-devel] vfio for platform devices - 9/5/2012 - minutes

[Sethi Varun-B16395]

I have a query about the ARM SMMU driver. In the ARM smmu driver I see, that 
bus notifiers are registered for both amba and platform bus. Amba is the I/O 
interconnect, right? Why is bus notifier required for the amba bus?
 
-Varun

> -----Original Message-----
> From: Yoder Stuart-B08248
> Sent: Thursday, September 05, 2013 11:21 PM
> To: Wood Scott-B07421; Sethi Varun-B16395; Bhushan Bharat-R65777; 'Peter
> Maydell'; 'Santosh Shukla'; 'Alex Williamson'; 'Alexander Graf';
> 'Antonios Motakis'; 'Christoffer Dall'; 'address@hidden'
> Cc: address@hidden; address@hidden; qemu-
> address@hidden
> Subject: vfio for platform devices - 9/5/2012 - minutes
> 
> 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