Re: [RFC PATCH v3 0/3] vfio: platform: return device properties for a platform device

[Alex Williamson <alex.williamson-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Thu, 2015-08-27 at 14:52 +0200, Eric Auger wrote:
> Hi Baptiste, Antonios,
> 
> What are the plans wrt this series? I am currently integrating another
> QEMU VFIO platform devices where this series could be useful I think
> (Feb 2015). Do you intend to follow up and bring it upstream?
> 
> Alex, do you see some show-stoppers in this series or do you advise to
> simply follow-up?

I'm at a bit of a disadvantage not really knowing what types of
properties a user will be able to retrieve here.  The interface itself
seems sort of like a game of Go Fish.  Should the properties we're
looking for be generally available via sysfs?  The ioctl proposed needs
some work to fit within the argsz/flags model that vfio typically uses.
It's unclear what argsz vs length represents and defining the flags
field as 'type' limits the future extensions of the ioctl.  Thanks,

Alex

> On 12/19/2014 10:20 PM, Antonios Motakis wrote:
> > This RFC's intention is to show what an interface to access device
> > properties for the VFIO platform driver can look like. These properties
> > can be from the device tree node describing the device, or ACPI properties
> > in the future.
> > 
> > If a device property corresponding to a platform device bound by VFIO PLATFORM
> > or VFIO AMBA is available, this patch series will allow the user to query
> > for this information. This can be useful for userspace drivers to automatically
> > query parameters related to the device.
> > 
> > Specifically for QEMU, reading the "compatible" property of the device tree
> > node could be of use to find out what device is being assigned to the guest and
> > handle appropriately a wider range of devices in the future, and to generate an
> > appropriate device tree for the guest.
> > 
> > Older versions of this series where specifically targeted at device tree
> > properties. This version has been reworked on top of Rafael J. Wysocki's
> > uniform device properties API for device tree and ACPI devices. This will allow
> > us to use the API in the future with devices described via ACPI.
> > 
> > This also means a kernel including the uniform device properties API is needed
> > to apply these patches, in additon to the VFIO patches, e.g. branch pm+acpi-3.19-rc1
> > from https://git.kernel.org/cgit/linux/kernel/git/rafael/linux-pm.git/
> > 
> > The API to get the list of available properties and the device tree full_name
> > have been removed. These probably don't serve an useful purpose, as the user
> > of this API need to know anyway what properties are specific to the device he
> > wants to access with VFIO. If we decide to reintroduce the list of properties
> > in the future, the generic device properties API in the kernel will have to
> > be extended accordingly.
> > 
> > A kernel with this series and all the dependencies applied can be pulled from
> > branch vfio-device-properties-v3 from the repository:
> > https://github.com/virtualopensystems/linux-kvm-arm.git
> > 
> > Changes since v2:
> >  - Reworked on top of Rafael J. Wysocki's uniform device properties API for
> >    device tree and ACPI
> >  - Support for u64 array properties
> >  - Removed API to get list of available properties and device tree full_name
> > Changes since v1:
> >  - Updated for VFIO platform patch series v8:
> >    VFIO AMBA devices now supported in addition to VFIO PLATFORM devices
> >  - Refactored and cleaned up the code
> > 
> > Antonios Motakis (3):
> >   vfio: platform: add device properties skeleton and user API
> >   vfio: platform: access device property as a list of strings
> >   vfio: platform: return device properties as arrays of unsigned
> >     integers
> > 
> >  drivers/vfio/platform/Makefile                |   3 +-
> >  drivers/vfio/platform/properties.c            | 162 ++++++++++++++++++++++++++
> >  drivers/vfio/platform/vfio_platform_common.c  |  35 ++++++
> >  drivers/vfio/platform/vfio_platform_private.h |   7 ++
> >  include/uapi/linux/vfio.h                     |  26 +++++
> >  5 files changed, 232 insertions(+), 1 deletion(-)
> >  create mode 100644 drivers/vfio/platform/properties.c
> > 
>