[PATCH v5 0/8] Add SCMI Virtio & Clock atomic support

[Cristian Marussi]

Hi,

This small series is the tail-subset of the previous V8 series about atomic
support in SCMI [1], whose 8-patches head-subset has now been queued on
[2]; as such, it is based on [2] on top of tag scmi-updates-5.17:

commit 94d0cd1da14a ("firmware: arm_scmi: Add new parameter to
		     mark_txdone")

Patch [1/8] substitute virtio-scmi ready flag and lock with a reference
counter to keep track of vio channels lifetime while removing the need of
a wide spinlocked section (that would cause issues with introduction of
virtio polling support)

Patch [2/8] adds a few helpers to handle the TX free_list and a dedicated
spinlock to reduce the reliance on the main one.

Patch [3/8] adds polling mode to SCMI VirtIO transport in order to support
atomic operations on such transport.

Patches [4,5/8] introduce a new optional SCMI binding, atomic-threshold-us,
to configure a platform specific time threshold used in the following
patches to select with a finer grain which SCMI resources should be
eligible for atomic operations when requested.

Patch [6/8] exposes new SCMI Clock protocol operations to allow an SCMI
user to request atomic mode on clock enable commands.

Patch [7/8] adds support to SCMI Clock protocol for a new clock attributes
field which advertises typical enable latency for a specific resource.

Finally patch [8/8] add support for atomic operations to the SCMI clock
driver; the underlying logic here is that we register with the Clock
framework atomic-capable clock resources if and only if the backing SCMI
transport is capable of atomic operations AND the specific clock resource
has been advertised by the SCMI platform as having:

	clock_enable_latency <= atomic-threshold-us

The idea is to avoid costly atomic busy-waiting for resources that have
been advertised as 'slow' to operate upon. (i.e. a PLL vs a gating clock)

To ease testing the whole series can be find at [3].

Any feedback/testing welcome as usual.

Thanks,
Cristian

[1]: https://lore.kernel.org/linux-arm-kernel/20211220195646.44498-1-cristian.marussi@arm.com/
[2]: https://git.kernel.org/pub/scm/linux/kernel/git/sudeep.holla/linux.git/tag/?h=scmi-updates-5.17
[3]: https://gitlab.arm.com/linux-arm/linux-cm/-/commits/scmi_atomic_clk_virtio_V5/

---
v4 --> v5
- dt_bindings: fixed example and removed dtschema warnings/errors
- dt_bindings: added 'default: 0' clause
- introduced vio_msg refcounts and helpers to avoid premature reuse of
  freed messages when both poling and IRQ path are active on a buffer
- better handling of timed out polled messages on late replies using
  new VIO_MSG_POLL_TIMEOUT state
- fixed comments on locks
- removed unneeded virtqueue re-enable when fail to acquire channel in
  complete_cb

V3 --> V4
- renamed optional DT property to atomic-threshold-us

V2 --> V3
 - split out virtio_ring RFC patch into a distinct series
 - calling virtqueue_broke_device when cleaning up channel
 - removed RFC tags from CLK related patches

V1 --> V2
 - added vio channel refcount support patch
 - reviewed free_list support and usage
 - added virtio_ring RFC patch
 - shrinked spinlocked section within virtio_poll_done to exclude
   virtqueue_poll call
 - removed poll_lock
 - use vio channel refcount acquire/release logic when polling
 - using new free_list accessors
 - added new dedicated pending_lock to access pending_cmds_list
 - fixed a few comments

Cristian Marussi (8):
  firmware: arm_scmi: Add a virtio channel refcount
  firmware: arm_scmi: Review virtio free_list handling
  firmware: arm_scmi: Add atomic mode support to virtio transport
  dt-bindings: firmware: arm,scmi: Add atomic-threshold-us optional
    property
  firmware: arm_scmi: Support optional system wide atomic-threshold-us
  firmware: arm_scmi: Add atomic support to clock protocol
  firmware: arm_scmi: Add support for clock_enable_latency
  clk: scmi: Support atomic clock enable/disable API

 .../bindings/firmware/arm,scmi.yaml           |  10 +
 drivers/clk/clk-scmi.c                        |  71 ++-
 drivers/firmware/arm_scmi/Kconfig             |  15 +
 drivers/firmware/arm_scmi/clock.c             |  34 +-
 drivers/firmware/arm_scmi/driver.c            |  33 +-
 drivers/firmware/arm_scmi/virtio.c            | 591 +++++++++++++++---
 include/linux/scmi_protocol.h                 |   9 +-
 7 files changed, 655 insertions(+), 108 deletions(-)

-- 
2.17.1