[PATCH v3 0/3] thermal/netlink/intel_hfi: Enable HFI feature only when required

[Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>]

The patchset introduces a new genetlink family bind/unbind callbacks
and thermal/netlink notifications, which allow drivers to send netlink
multicast events based on the presence of actual user-space consumers.
This functionality optimizes resource usage by allowing disabling
of features when not needed.

Then implement the notification mechanism in the intel_hif driver,
it is utilized to disable the Hardware Feedback Interface (HFI)
dynamically. By implementing a thermal genl notify callback, the driver
can now enable or disable the HFI based on actual demand, particularly
when user-space applications like intel-speed-select or Intel Low Power
daemon utilize events related to performance and energy efficiency
capabilities.

On machines where Intel HFI is present, but there are no user-space
components installed, we can save tons of CPU cycles.

Changes v2 -> v3:

- Fix unused variable compilation warning
- Add missed Suggested by tag to patch2
 
Changes v1 -> v2:

- Rewrite using netlink_bind/netlink_unbind callbacks.

- Minor changelog tweaks.

- Add missing check in intel hfi syscore resume (had it on my testing,
but somehow missed in post).

- Do not use netlink_has_listeners() any longer, use custom counter instead.
To keep using netlink_has_listners() would be required to rearrange 
netlink_setsockopt() and possibly netlink_bind() functions, to call 
nlk->netlink_bind() after listeners are updated. So I decided to custom
counter. This have potential issue as thermal netlink registers before
intel_hif, so theoretically intel_hif can miss events. But since both
are required to be kernel build-in (if CONFIG_INTEL_HFI_THERMAL is
configured), they start before any user-space.

v1: https://lore.kernel.org/linux-pm/20240131120535.933424-1-stanislaw.gruszka@linux.intel.com//
v2: https://lore.kernel.org/linux-pm/20240206133605.1518373-1-stanislaw.gruszka@linux.intel.com/

Stanislaw Gruszka (3):
  genetlink: Add per family bind/unbind callbacks
  thermal: netlink: Add genetlink bind/unbind notifications
  thermal: intel: hfi: Enable interface only when required

 drivers/thermal/intel/intel_hfi.c | 95 +++++++++++++++++++++++++++----
 drivers/thermal/thermal_netlink.c | 40 +++++++++++--
 drivers/thermal/thermal_netlink.h | 25 ++++++++
 include/net/genetlink.h           |  4 ++
 net/netlink/genetlink.c           | 30 ++++++++++
 5 files changed, 179 insertions(+), 15 deletions(-)

-- 
2.34.1