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Rafael J. Wysocki 3ad5df2391 ACPI: PNP: Drop PNP0C01 and PNP0C02 from acpi_pnp_device_ids[]
There is a long-standing problem with ACPI device enumeration that
if the given device has a compatible ID which is one of the generic
system resource device IDs (PNP0C01 and PNP0C02), it will be claimed
by the PNP scan handler and it will not be represented as a platform
device, so it cannot be handled by a platform driver.

Drivers have been working around this issue by "manually" creating
platform devices that they can bind to (see the Intel HID driver for
one example) or adding their device IDs to acpi_nonpnp_device_ids[].
None of the above is particularly clean though and the only reason why
the PNP0C01 and PNP0C02 device IDs are present in acpi_pnp_device_ids[]
is to allow the legacy PNP system driver to bind to those devices and
reserve their resources so they are not used going forward.

Obviously, to address this problem PNP0C01 and PNP0C02 need to be
dropped from acpi_pnp_device_ids[], but doing so without making any
other changes would be problematic because the ACPI core would then
create platform devices for the generic system resource device objects
and that would not work on all systems for two reasons.  First, the
PNP system driver explicitly avoids reserving I/O resources below the
"standard PC hardware" boundary, 0x100, to avoid conflicts in that range
(one possible case when this may happen is when the CMOS RTC driver is
involved), but the platform device creation code does not do that.
Second, there may be resource conflicts between the "system" devices and
the other devices in the system, possibly including conflicts with PCI
BARs.  Registering the PNP system driver via fs_initcall() helps to
manage those conflicts, even though it does not make them go away.
Resource conflicts during the registration of "motherboard resources"
that occur after PCI has claimed BARs are harmless as a rule and do
not need to be addressed in any specific way.

To overcome the issues mentioned above, use the observation that it
is not actually necessary to create any device objects in addition
to struct acpi_device ones in order to reserve the "system" device
resources because that can be done directly in the ACPI device
enumeration code.

Namely, modify acpi_default_enumeration() to add the given ACPI device
object to a special "system devices" list if its _HID is either PNP0C01
or PNP0C02 without creating a platform device for it.  Next, add a new
special acpi_scan_claim_resources() function that will be run via
fs_initcall() and will walk that list and reserve resources for each
device in it along the lines of what the PNP system driver does.

Having made the above changes, drop PNP0C01 and PNP0C02 from
acpi_pnp_device_ids[] which will allow platform devices to be created
for ACPI device objects whose _CID lists contain PNP0C01 or PNP0C02,
but the _HID is not in acpi_pnp_device_ids[].

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
[ rjw: Drop a leftover comment and add a new one elsewhere ]
Link: https://patch.msgid.link/9550709.CDJkKcVGEf@rafael.j.wysocki
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
History 2025-12-16 21:50:30 +01:00
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Linux kernel
============

The Linux kernel is the core of any Linux operating system. It manages hardware,
system resources, and provides the fundamental services for all other software.

Quick Start
-----------

* Report a bug: See Documentation/admin-guide/reporting-issues.rst
* Get the latest kernel: https://kernel.org
* Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst
* Join the community: https://lore.kernel.org/

Essential Documentation
-----------------------

All users should be familiar with:

* Building requirements: Documentation/process/changes.rst
* Code of Conduct: Documentation/process/code-of-conduct.rst
* License: See COPYING

Documentation can be built with make htmldocs or viewed online at:
https://www.kernel.org/doc/html/latest/


Who Are You?
============

Find your role below:

* New Kernel Developer - Getting started with kernel development
* Academic Researcher - Studying kernel internals and architecture
* Security Expert - Hardening and vulnerability analysis
* Backport/Maintenance Engineer - Maintaining stable kernels
* System Administrator - Configuring and troubleshooting
* Maintainer - Leading subsystems and reviewing patches
* Hardware Vendor - Writing drivers for new hardware
* Distribution Maintainer - Packaging kernels for distros


For Specific Users
==================

New Kernel Developer
--------------------

Welcome! Start your kernel development journey here:

* Getting Started: Documentation/process/development-process.rst
* Your First Patch: Documentation/process/submitting-patches.rst
* Coding Style: Documentation/process/coding-style.rst
* Build System: Documentation/kbuild/index.rst
* Development Tools: Documentation/dev-tools/index.rst
* Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst
* Core APIs: Documentation/core-api/index.rst

Academic Researcher
-------------------

Explore the kernel's architecture and internals:

* Researcher Guidelines: Documentation/process/researcher-guidelines.rst
* Memory Management: Documentation/mm/index.rst
* Scheduler: Documentation/scheduler/index.rst
* Networking Stack: Documentation/networking/index.rst
* Filesystems: Documentation/filesystems/index.rst
* RCU (Read-Copy Update): Documentation/RCU/index.rst
* Locking Primitives: Documentation/locking/index.rst
* Power Management: Documentation/power/index.rst

Security Expert
---------------

Security documentation and hardening guides:

* Security Documentation: Documentation/security/index.rst
* LSM Development: Documentation/security/lsm-development.rst
* Self Protection: Documentation/security/self-protection.rst
* Reporting Vulnerabilities: Documentation/process/security-bugs.rst
* CVE Procedures: Documentation/process/cve.rst
* Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst
* Security Features: Documentation/userspace-api/seccomp_filter.rst

Backport/Maintenance Engineer
-----------------------------

Maintain and stabilize kernel versions:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* Backporting Guide: Documentation/process/backporting.rst
* Applying Patches: Documentation/process/applying-patches.rst
* Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git for Maintainers: Documentation/maintainer/configure-git.rst

System Administrator
--------------------

Configure, tune, and troubleshoot Linux systems:

* Admin Guide: Documentation/admin-guide/index.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst
* Tracing/Debugging: Documentation/trace/index.rst
* Performance Security: Documentation/admin-guide/perf-security.rst
* Hardware Monitoring: Documentation/hwmon/index.rst

Maintainer
----------

Lead kernel subsystems and manage contributions:

* Maintainer Handbook: Documentation/maintainer/index.rst
* Pull Requests: Documentation/maintainer/pull-requests.rst
* Managing Patches: Documentation/maintainer/modifying-patches.rst
* Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst
* Development Process: Documentation/process/maintainer-handbooks.rst
* Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git Configuration: Documentation/maintainer/configure-git.rst

Hardware Vendor
---------------

Write drivers and support new hardware:

* Driver API Guide: Documentation/driver-api/index.rst
* Driver Model: Documentation/driver-api/driver-model/driver.rst
* Device Drivers: Documentation/driver-api/infrastructure.rst
* Bus Types: Documentation/driver-api/driver-model/bus.rst
* Device Tree Bindings: Documentation/devicetree/bindings/
* Power Management: Documentation/driver-api/pm/index.rst
* DMA API: Documentation/core-api/dma-api.rst

Distribution Maintainer
-----------------------

Package and distribute the kernel:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* ABI Documentation: Documentation/ABI/README
* Kernel Configuration: Documentation/kbuild/kconfig.rst
* Module Signing: Documentation/admin-guide/module-signing.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst



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=========================

* Mailing Lists: https://lore.kernel.org/
* IRC: #kernelnewbies on irc.oftc.net
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* MAINTAINERS file: Lists subsystem maintainers and mailing lists
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