[RFC PATCH 0/1] cpufreq: virtio frontend to report host CPU frequency

[Baorui.Liu <baorliu@amd.com>]

This RFC adds a guest virtio-cpufreq frontend so a VM can read the
host frequency of the pCPU that currently runs a given vCPU.

Context
=======
Android batterystats needs cpufreq together with power_profile.xml.
A Xen Android guest cannot read host sysfs, so QEMU already has a
backend (virtio device id 42) that returns xc_get_cpufreq_avgfreq()
for the pinned pCPU. This patch is the Linux frontend.

Why not virtual-cpufreq.c
=========================
drivers/cpufreq/virtual-cpufreq.c is an MMIO guest driver. This
stack is virtio + Xen/QEMU, so a separate frontend is used. Feedback
on folding into or sharing infrastructure with virtual-cpufreq is
welcome.

Known RFC issues
================
- Virtio device id 42 is not allocated by the OASIS virtio spec.
- The OPP table is hardcoded (1400/1700/3000 kHz) for bring-up.
- The QEMU backend is a separate series (not this patch).
- .get() waits on a virtqueue and may sleep.

Please comment on the id allocation, protocol, and whether this
belongs in linux-pm as RFC before a formal PATCH.

Baorui.Liu (1):
  cpufreq: virtio: add driver to report host frequency to guests

 drivers/cpufreq/Kconfig          |  14 ++
 drivers/cpufreq/Makefile         |   1 +
 drivers/cpufreq/virtio-cpufreq.c | 235 +++++++++++++++++++++++++++++++
 include/uapi/linux/virtio_ids.h  |   1 +
 4 files changed, 251 insertions(+)
 create mode 100644 drivers/cpufreq/virtio-cpufreq.c

-- 
2.34.1