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[ Upstream commit c33c43f71bda362b292a6e57ac41b64342dc87b3 ] On certain Loongson platforms, drivers attempting to request a legacy ISA IRQ directly via request_irq() (e.g., IRQ 4) may fail. The virtual IRQ descriptor is not fully initialized and lacks a valid irqchip. This issue does not affect ACPI-enumerated devices described in DSDT, as their interrupts are properly mapped via the GSI translation path. This indicates the LPC irqdomain itself is functional but is not correctly handling direct VIRQ-to-HWIRQ mappings. The root cause is the use of irq_domain_create_linear(). This API sets up a domain for dynamic, on-demand mapping, typically triggered by a GSI request. It does not pre-populate the mappings for the legacy VIRQ range (0-15). Consequently, if no ACPI device claims a specific GSI (e.g., GSI 4), the corresponding VIRQ (e.g., VIRQ 4) is never mapped to the LPC domain. A direct call to request_irq(4, ...) then fails because the kernel cannot resolve this VIRQ to a hardware interrupt managed by the LPC controller. The PCH-LPC interrupt controller is an i8259-compatible legacy device that requires a deterministic, static 1-to-1 mapping for IRQs 0-15 to support legacy drivers. Fix this by replacing irq_domain_create_linear() with irq_domain_create_legacy(). This API is specifically designed for such controllers. It establishes the required static 1-to-1 VIRQ-to-HWIRQ mapping for the entire legacy range (0-15) immediately upon domain creation. This ensures that any VIRQ in this range is always resolvable, making direct calls to request_irq() for legacy IRQs function correctly. Signed-off-by: Ming Wang <wangming01@loongson.cn> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.