platform/x86: firmware_attributes_class: Add a high level API

Hi all,

After my discussion with Joshua on v2, I realized the API I made was not
ergonomic at all and it didn't exactly respond to driver needs. In this
version I tried a completely different approach and IMO it's much much
better now.

First of all I adopted standard sysfs terminology for everything. A
"firmware attribute" is just an attribute_group under the attributes/
directory so everything related to this concept is just called "group"
now. Everything refered as properties in the previous patch are now just
plain "attributes".

This new API revolves around the `fwat_{bool,enum,int,str}_data`
structs. These hold all the metadata a "firmware_attribute" of that
given type needs.

These structs also hold `read` and `write` callbacks for the
current_value attribute, because obviously that value is always dynamic.
However the rest of attributes (default_value, display_name, min, max,
etc) are constant.

In the simple case this metadata structs can be defined statically with
DEFINE_FWAT_{BOOL,ENUM,INT,STR}_GROUP() macros. However most users of
this class obtain this values dynamically so you can also define this
structs dynamically.

In the end all groups (static and dynamic) will be created using
fwat_create_group() after registering the class device.

Let me know what you think, your feedback is very appreciated :)

I do have one question for anyone interested. Should constraints over
the current_value (such as min, max, increment, etc.) be enforced at the
show/store level? i.e. before values reach read/write callbacks.

Signed-off-by: Kurt Borja <kuurtb@gmail.com>
---
Changes in v4:

[Patch 1]
  - Embbed a device in fwat_device instead of a kobject.
  - Instead of an attrs_kobj root kobj, create a kset with the same
    name.
[Patch 2]
  - Add a (*show_override) callback in fwat_group_data.
  - Instead of allocating and filling sysfs groups and attributes
    manually, I defined custom ktypes for each fwat type. All groups are
    now statically defined and added through default_groups.

    I think this is a BIG optimization in terms of memory at least. Also
    fwat_group memory is now managed by a kobject which is allocated one
    time. This is also a less impactful performance optimization (less
    individual allocations).
  - No changes to API :) (I take suggestions though)

I might have lost some of the changelog. Sorry for that!

- Link to v3: https://lore.kernel.org/r/20250621-fw-attrs-api-v3-0-3dd5...

Changes in v3:

[Patch 1]
- Fixed UAF in fwat_device_unregister(). Device was unregistered after
  freeing fadev.
[Patch 2]
- Patch 2 was completely replaced. A new approach for the API is taken,
  based on Joshua's suggestions.

- Link to v2: https://lore.kernel.org/r/20250517-fw-attrs-api-v2-0-fa1a...

Changes in v2:

[Patch 1]
 - Include kdev_t.h header
[Patch 2]
 - Use one line comments in fwat_create_attrs()
 - Check propagate errors in fwat_create_attrs()
 - Add `mode` to fwat_attr_config and related macros to let users
   configure the `current_value` attribute mode
 - Use defined structs in fwat_attr_ops instead of anonymous ones
 - Move fwat_attr_type from config to ops
[Patch 5]
 - Just transition to new API without chaing ABI

- Link to v1: https://lore.kernel.org/r/20250509-fw-attrs-api-v1-0-258a...

---
Kurt Borja (5):
      platform/x86: firmware_attributes_class: Add high level API for the attributes interface
      platform/x86: firmware_attributes_class: Move header to include directory
      platform/x86: samsung-galaxybook: Transition new firmware_attributes API
      Documentation: ABI: Update sysfs-class-firmware-attributes documentation
      MAINTAINERS: Add FIRMWARE ATTRIBUTES CLASS entry

Thomas Weißschuh (1):
      platform/x86: firmware_attributes_class: Add device initialization methods

 .../ABI/testing/sysfs-class-firmware-attributes    |   1 +
 MAINTAINERS                                        |   8 +
 drivers/platform/x86/dell/dell-wmi-sysman/sysman.c |   2 +-
 drivers/platform/x86/firmware_attributes_class.c   | 659 ++++++++++++++++++++-
 drivers/platform/x86/firmware_attributes_class.h   |  12 -
 drivers/platform/x86/hp/hp-bioscfg/bioscfg.c       |   2 +-
 drivers/platform/x86/lenovo/think-lmi.c            |   2 +-
 drivers/platform/x86/samsung-galaxybook.c          | 246 ++------
 include/linux/firmware_attributes_class.h          | 375 ++++++++++++
 9 files changed, 1107 insertions(+), 200 deletions(-)
---
base-commit: 73f0f2b52c5ea67b3140b23f58d8079d158839c8
change-id: 20250326-fw-attrs-api-0eea7c0225b6
-- 
 ~ Kurt