linux-kernel - Re: [PATCH v2 0/9] platform/wmi: Introduce marshalling support

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Message-ID: <24598820-dcd8-4e29-9c1b-58b5fdba144d@gmx.de>
Date: Tue, 6 Jan 2026 16:15:22 +0100
From: Armin Wolf <W_Armin@....de>
To: hansg@...nel.org, ilpo.jarvinen@...ux.intel.com
Cc: platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux@...ssschuh.net, Dell.Client.Kernel@...l.com, corbet@....net,
 linux-doc@...r.kernel.org
Subject: Re: [PATCH v2 0/9] platform/wmi: Introduce marshalling support

Am 20.12.25 um 21:46 schrieb Armin Wolf:

> The Windows WMI-ACPI driver likely uses wmilib [1] to interact with
> the WMI service in userspace. Said library uses plain byte buffers
> for exchanging data, so the WMI-ACPI driver has to convert between
> those byte buffers and ACPI objects returned by the ACPI firmware.
>
> The format of the byte buffer is publicly documented [2], and after
> some reverse eingineering of the WMI-ACPI driver using a set of custom
> ACPI tables, the following conversion rules have been discovered:
>
> - ACPI integers are always converted into a uint32
> - ACPI strings are converted into special WMI strings
> - ACPI buffers are copied as-is
> - ACPI packages are unpacked
>
> Extending the ACPI-WMI to perform this kind of marshalling for WMI
> data blocks, methods and events would give us a number of benefits:
>
> - WMI drivers are not restricted to a fixed set of supported ACPI data
>    types anymore, see dell-wmi-aio (integer vs buffer) and
>    hp-wmi-sensors (string vs buffer)
>
> - correct marshalling of WMI strings when data blocks are marked
>    as requiring ACPI strings instead of ACPI buffers
>
> - development of WMI drivers without having to understand ACPI
>
> This eventually should result in better compatibility with some
> ACPI firmware implementations and in simpler WMI drivers.
>
> The first patch extends the WMI driver core to perform said
> marshalling as well as a new API not based on ACPI objects. The next
> patch adds a KUnit test for testing the marshalling code. The
> following two patches then add a set of helper functions for dealing
> with WMI string data together with another KUnit test.
>
> The remaining patches then convert some simple WMI drivers to use the
> new WMI API and update the driver development guide so that new WMI
> drivers stop using the ACPI-based API.
>
> The series has been tested on multiple machines, with the xiaomi-wmi
> and intel-wmi-sbl-fw-update being tested using a set of custom ACPI
> tables loaded over configFS.
>
> [1] https://learn.microsoft.com/de-de/windows-hardware/drivers/ddi/wmilib/

Any thoughts on this? I can split the last five patches into a separate patch series
when necessary.

Thanks,
Armin Wolf

> Changes since v1:
> - fix spelling issues inside the documentation
> - add Reviewed-by tag for the documentation
>
> Armin Wolf (9):
>    platform/wmi: Introduce marshalling support
>    platform/wmi: Add kunit test for the marshalling code
>    platform/wmi: Add helper functions for WMI string conversions
>    platform/wmi: Add kunit test for the string conversion code
>    platform/x86: intel-wmi-sbl-fw-update: Use new buffer-based WMI API
>    platform/x86/intel/wmi: thunderbolt: Use new buffer-based WMI API
>    platform/x86: xiaomi-wmi: Use new buffer-based WMI API
>    platform/x86: wmi-bmof: Use new buffer-based WMI API
>    platform/wmi: Update driver development guide
>
>   Documentation/driver-api/wmi.rst              |   3 +
>   Documentation/wmi/acpi-interface.rst          |  68 +++
>   .../wmi/driver-development-guide.rst          |  76 ++-
>   drivers/platform/wmi/Kconfig                  |   3 +
>   drivers/platform/wmi/Makefile                 |   5 +-
>   drivers/platform/wmi/core.c                   | 160 ++++++-
>   drivers/platform/wmi/internal.h               |  14 +
>   drivers/platform/wmi/marshalling.c            | 233 +++++++++
>   drivers/platform/wmi/string.c                 |  92 ++++
>   drivers/platform/wmi/tests/Kconfig            |  27 ++
>   drivers/platform/wmi/tests/Makefile           |  11 +
>   .../platform/wmi/tests/marshalling_kunit.c    | 448 ++++++++++++++++++
>   drivers/platform/wmi/tests/string_kunit.c     | 277 +++++++++++
>   .../platform/x86/intel/wmi/sbl-fw-update.c    |  43 +-
>   drivers/platform/x86/intel/wmi/thunderbolt.c  |  26 +-
>   drivers/platform/x86/wmi-bmof.c               |  34 +-
>   drivers/platform/x86/xiaomi-wmi.c             |   5 +-
>   include/linux/wmi.h                           |  44 +-
>   18 files changed, 1477 insertions(+), 92 deletions(-)
>   create mode 100644 drivers/platform/wmi/internal.h
>   create mode 100644 drivers/platform/wmi/marshalling.c
>   create mode 100644 drivers/platform/wmi/string.c
>   create mode 100644 drivers/platform/wmi/tests/Kconfig
>   create mode 100644 drivers/platform/wmi/tests/Makefile
>   create mode 100644 drivers/platform/wmi/tests/marshalling_kunit.c
>   create mode 100644 drivers/platform/wmi/tests/string_kunit.c
>