PA-RISC Linux Kernel
Nothing to brag about, but it's important, so let's keep it visible: Kernel hotspots and problems (KnownIssues).
The kernel comes in two flavours: 32 bit and 64 bit. The older machines (PA 7xxx processors) only run the 32 bit kernel. Newer machines (PA8xxx processors) may run either 32 or 64 bit kernels. Some machines (depending on the PDC firmware) may only run the 64 bit kernel. The user land is currently only 32 bit ELF, which means that the only interest in running a 64 bit kernel on machines capable of running 32 and 64 bit is accessing more than 4GB of RAM.
Low Level Kernel Code
A collection of notes about various parts of the PA-RISC low level Linux kernel code can be found here:
* VirtualMemorySubsystem * SMP implementation * DiscontiguousMemorySupport * DeviceDrivers and interaction with the DeviceModel * Interrupts and IO-SAPIC * EISA, GSC, PCI and IO-MMU implementations * FutexImplementation * Locks and AtomicOperations * Time and high-precision timers. * Registers and SpaceRegisters
Specific Device Drivers
Here are some drivers that have been written specially for the PA-RISC Linux port, as they concern either PA-RISC-specific devices, or "generic" devices that are only found in PA-RISC systems.
* STIFrameBuffer and STIConsole * AD1889 PCI Soundmax Controller * HarmonyAudio * SuperIO * HIL bus and drivers
Also some bits about PA-RISC specific hardware/firmware and the way it is used by the kernel:
* ProcessorDependentCode (PDC) * GuardianServiceProcessor (GSP) * ConsoleTypes
Bits of information related to the Linux Kernel but not specific to PA-RISC
* Sparse compile-time checks for the Linux kernel * KernelProfiling