[PATCH v8 00/17] Introduce a unified API for SCMI Server testing

Cristian Marussi
2023-01-18T12:18:26Z

Hi all,

This series aims to introduce a new SCMI unified userspace interface meant
to ease testing an SCMI Server implementation for compliance, fuzzing etc.,
from the perspective of the OSPM agent (non-secure world only ...)

It is proposed as a testing/development facility, it is NOT meant to be a
feature to use in production, but only enabled in Kconfig for test
deployments.

Currently an SCMI Compliance Suite like the one at [1] can only work by
injecting SCMI messages at the SCMI transport layer using the mailbox test
driver (CONFIG_MAILBOX_TEST) via its few debugfs entries and looking at
the related replies from the SCMI backend Server.

This approach has a few drawbacks:

- the SCMI Server under test MUST be reachable through a mailbox based
SCMI transport: any other SCMI Server placement is not possible (like in
a VM reachable via SCMI Virtio). In order to cover other placements in
the current scenario we should write some sort of test driver for each
and every existent SCMI transport and for any future additional transport
...this clearly does not scale.

- even in the mailbox case the userspace Compliance suite cannot simply
send and receive bare SCMI messages BUT it has to properly lay them out
into the shared memory exposed by the mailbox test driver as expected by
the transport definitions. In other words such a userspace test
application has to, not only use a proper transport driver for the system
at hand, but it also has to have a comprehensive knowledge of the
internals of the underlying transport in order to operate.

- last but not least, the system under test has to be specifically
configured and built, in terms of Kconfig and DT, to perform such kind of
testing, it cannot be used for anything else, which is unfortunate for
CI/CD deployments.

This series introduces a new SCMI Raw mode support feature that, when
configured and enabled exposes a new interface in debugfs through which:

- a userspace application can inject bare SCMI binary messages into the
SCMI core stack; such messages will be routed by the SCMI regular kernel
stack to the backend Server using the currently configured transport
transparently: in other words you can test the SCMI server, no matter
where it is placed, as long as it is reachable from the currently
configured SCMI stack.
Same goes the other way around on the reading path: any SCMI server reply
can be read as a bare SCMI binary message from the same debugfs path.

- as a direct consequence of this way of injecting bare messages in the
middle of the SCMI stack (instead of beneath it at the transport layer)
the user application has to handle only bare SCMI messages without having
to worry about the specific underlying transport internals that will be
taken care of by the SCMI core stack itself using its own machinery,
without duplicating such logic.

- a system under test, once configured with SCMI Raw support enabled in
Kconfig, can be booted without any particular DT change.

Latest V6 additions:

- improved scmi traces for msg dumps to include used channels
- added a new common SCMI debugfs root fs
- reworked SCMI Raw debugfs layout
- added support of a new additional per-channel API that allows a user to
select a specific egress channel for the message injection (when more
than one channel is available)

A quick and trivial example from the shell...reading from a sensor by
injecting a properly crafted packet in raw mode (letting the stack select
the channel):

# INJECT THE SENSOR_READING MESSAGE FOR SENSOR ID=1 (binary little endian)
root@deb-buster-arm64:~# echo -e -n \\x06\\x54\\x00\\x00\\x01\\x00\\x00\\x00\\x00\\x00\\x00\\x00 > /sys/kernel/debug/scmi/0/raw/message

# READING BACK THE REPLY...
root@deb-buster-arm64:~# cat /sys/kernel/debug/scmi/0/raw/message | od --endian=little -t x4
0000000 00005406 00000000 00000335 00000000
0000020

while doing that, since Raw mode makes (partial) use of the regular SCMI
stack, you can observe the messages going through the SCMI stack with the
usual traces:

bash-329 [000] ..... 14183.446808: scmi_msg_dump: id=0 ch=10 pt=15 t=cmnd msg_id=06 seq=0000 s=0 pyld=0100000000000000
irq/35-mhu_db_l-81 [000] ..... 14183.447809: scmi_msg_dump: id=0 ch=10 pt=15 t=resp msg_id=06 seq=0000 s=0 pyld=3503000000000000

..trying to read in async when the backend server does NOT supports asyncs:

# AN ASYNC SENSOR READING REQUEST...
root@deb-buster-arm64:~# echo -e -n \\x06\\x54\\x00\\x00\\x01\\x00\\x00\\x00\\x01\\x00\\x00\\x00 > /sys/kernel/debug/scmi/0/raw/message_async

bash-329 [000] ..... 16415.938739: scmi_msg_dump: id=0 ch=10 pt=15 t=cmnd msg_id=06 seq=0000 s=0 pyld=0100000001000000
irq/35-mhu_db_l-81 [000] ..... 16415.944129: scmi_msg_dump: id=0 ch=10 pt=15 t=resp msg_id=06 seq=0000 s=-1 pyld=

# RETURNS A STATUS -1 FROM THE SERVER NOT SUPPORTING IT
root@deb-buster-arm64:~# cat /sys/kernel/debug/scmi/0/raw/message | od --endian=little -t x4
0000000 00005406 ffffffff
0000010

Note that the above example was on a JUNO, BUT exactly the same steps can
be used to reach an SCMI Server living on a VM reachable via virtio as
long as the system under test if properly configured to work with a
virtio transport.

In a nutshell the exposed API is as follows:

/sys/kernel/debug/scmi/
`-- 0
|-- atomic_threshold_us
|-- instance_name
|-- raw
| |-- channels
| | |-- 0x10
| | | |-- message
| | | `-- message_async
| | `-- 0x13
| | |-- message
| | `-- message_async
| |-- errors
| |-- message
| |-- message_async
| |-- notification
| `-- reset
`-- transport
|-- is_atomic
|-- max_msg_size
|-- max_rx_timeout_ms
|-- rx_max_msg
|-- tx_max_msg
`-- type

... where at the top level:

- <N>: a progressive sequence number identifying this SCMI instance, in
case there are multiple SCMI instance defined

- instance_name: can be used (by CI) to identify the SCMI instance <N>
that you are using through this Raw accessors: it corresponds to the SCMI
DT top node full name of the underlying SCMI instance

... rooted under /transport:

- a bunch of configuration info useful to setup the user application
expectations in terms of timeouts and message characteristics.

... rooted at /raw (the real SCMI Raw interface :D):

- message*: used to send sync/async commands and read back immediate and
delayed responses (if any)
- errors: used to report timeout and unexpected replies
- reset: used to reset the SCMI Raw stack, flushing all queues from
received messages still pending to be read out (useful to be sure to
cleanup between test suite runs...)
- notification: used to read any notification being spit by the system
(if previously enabled by the user app)

... rooted at /raw/channels/<M>/:

- message*: used to send sync/async commands and read back immediate and
delayed responses (if any), using a SPECIFIC transport channel <M>
(instead of letting the system choose for you based on transport config
and the rotocol embedded in the injected message)
NOTE THAT these entries are optional, created only if there is more than
transport channel defined on the system.

Each write corresponds to one command request and the replies or delayed
response are read back one message at time (receiving an EOF at each
message boundary).

The user application running the test is in charge of handling timeouts
and properly choosing SCMI sequence numbers for the outgoing requests: note
that the same fixed number can be re-used (...though discouraged...) as
long as the suite does NOT expect to send multiple in-flight commands
concurrently.

Since the SCMI core regular stack is partially used to deliver and collect
the messages, late replies after timeouts and any other sort of unexpected
message sent by the SCMI server platform back can be identified by the SCMI
core as usual and it will be reported under /errors for later analysis.
(a userspace test-app will have anyway properly detected the timeout on
/message* ...)

All of the above has been roughly tested against a standard JUNO SCP SCMI
Server (mailbox trans) and an emulated SCMI Server living in a VM (virtio
trans) using a custom experimental version of the scmi-tests Compliance
suite patched to support Raw mode and posted at [2]. (still in development
...merge requests are in progress...for now it is just a mean for me to
test the testing API ... O_o)

This V8 series is based on v6.2-rc1 PLUS another series which reworked a
bit the SCMI core stack init/probe [3]; to ease testing a V8 properly
based can be picked up from [4].

Having said that (in such a concise and brief way :P) ...

...any feedback/comments are welcome !

Thanks,
Cristian

---
v7 --> v8
- fixed a few bad handling on error path
- ignoring debugfs_ retvals as supposed to
- using XArray for per-channel queus instead of IDRs
- refactored debugfs setup calls

v6 --> v7
- fixed one sparse error
- removed redundant info.num_chans/channels fields: enumerate them dyamically
once needed.

v5 --> v6
- exported symbol debugfs_create_str
- rebased on top of v6.2-rc1 plus series at [3]
- redesigned SCMI debugfs layout with a bunch of common entries
enabled by implicit CONFIG_ARM_SCMI_NEED_DEBUGFS
- refactored SCMI Raw internal queues handling
- added SCMI Raw per-channel injection support
- added channels info on SCMI msg_dump traces
- fix debugfs multiple writers cases
- added DEBUG_FS dependency to Raw mode
- select CONFIG_ARM_SCMI_NEED_DEBUGFS when Raw mode is compiled

v4 --> v5
- rebased on sudeep/for-next/scmi
- added multiple SCMI instances support
- added optional Raw full-cohexistence mode
- use custom tags to distinguish Raw msg_dump traces
- add circular handling of raw buffers queues for errors and notifications

V3 --> v4
- rebased on v6.1-rc1
- addedd missing support for 'polled' transports and transport lacking a
completion_irq (like smc/optee)
- removed a few inlines
- refactored SCMI Raw RX patch to make use more extensively of the regular
non-Raw RX path
- fix handling of O_NONBLOCK raw_mode read requests

v2 --> v3
- fixed some sparse warning on LE and __poll_t
- reworked and simplified deferred worker in charge of xfer delayed waiting
- allow for injection of DT-unknown protocols messages when in Raw mode
(needed for any kind of fuzzing...)

v1 --> v2
- added comments and debugfs docs
- added dedicated transport devices for channels initialization
- better channels handling in Raw mode
- removed runtime enable, moved to static compile time exclusion
of SCMI regular stack

[1]: https://gitlab.arm.com/tests/scmi-tests
[2]: https://gitlab.arm.com/tests/scmi-tests/-/commits/raw_mode_support_devel/
[3]: https://lore.kernel.org/all/20221222185049.737625-1-cristian.marussi@arm.com/
[4]: https://gitlab.arm.com/linux-arm/linux-cm/-/commits/scmi_raw_mode_V8/

Cristian Marussi (17):
firmware: arm_scmi: Refactor xfer in-flight registration routines
firmware: arm_scmi: Refactor polling helpers
firmware: arm_scmi: Refactor scmi_wait_for_message_response
firmware: arm_scmi: Add flags field to xfer
firmware: arm_scmi: Add xfer Raw helpers
firmware: arm_scmi: Move errors defs and code to common.h
firmware: arm_scmi: Add internal platform/channel IDs
include: trace: Add platform and channel instance references
debugfs: Export debugfs_create_str symbol
firmware: arm_scmi: Populate a common SCMI debugsfs root
firmware: arm_scmi: Add debugfs ABI documentation for common entries
firmware: arm_scmi: Add core Raw transmission support
firmware: arm_scmi: Add debugfs ABI documentation for Raw mode
firmware: arm_scmi: Reject SCMI drivers while in Raw mode
firmware: arm_scmi: Call Raw mode hooks from the core stack
firmware: arm_scmi: Add Raw mode coexistence support
firmware: arm_scmi: Add per-channel Raw injection support

Documentation/ABI/testing/debugfs-scmi | 70 +
Documentation/ABI/testing/debugfs-scmi-raw | 109 ++
drivers/firmware/arm_scmi/Kconfig | 32 +
drivers/firmware/arm_scmi/Makefile | 1 +
drivers/firmware/arm_scmi/bus.c | 7 +
drivers/firmware/arm_scmi/common.h | 75 +
drivers/firmware/arm_scmi/driver.c | 638 +++++++--
drivers/firmware/arm_scmi/protocols.h | 7 +
drivers/firmware/arm_scmi/raw_mode.c | 1443 ++++++++++++++++++++
drivers/firmware/arm_scmi/raw_mode.h | 31 +
fs/debugfs/file.c | 1 +
include/trace/events/scmi.h | 18 +-
12 files changed, 2292 insertions(+), 140 deletions(-)
create mode 100644 Documentation/ABI/testing/debugfs-scmi
create mode 100644 Documentation/ABI/testing/debugfs-scmi-raw
create mode 100644 drivers/firmware/arm_scmi/raw_mode.c
create mode 100644 drivers/firmware/arm_scmi/raw_mode.h