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

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Feb 17, 2022 at 01:12:26PM +0000, Cristian Marussi wrote:
> 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


SCMI specific stuff so I don't have anything to add here.

By the way, it does not look like anything regarding SCMI atomic support
is needed in the virtio spec - is it true the interface with the device
is unaffected?

> [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
> 
> 
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