Hello,

This patch series introduces Device-Tree based CPU topology support
for ARM Xen.

This version incorporates the feedback received from Jan on the v3
submission. The main focus of this update includes transitioning 
towards a generic Kconfig structure, untangling header dependencies
and various code cleanups.

Future Work:
 - Support for the "credit2_runqueue=cluster" option.
 - CPU topology support for RISC-V and PPC (once SMP support is available).
 - Topology information generation from the ACPI PPTT.

Changes in v4:
 - Only display the CPU topology configuration prompt in common/Kconfig
   if the architecture defines HAS_GENERIC_CPU_TOPOLOGY.
 - Move the definition of the global 'cpu_topology' pointer to
   common/cpu-topology.c.
 - Update the Makefile to explicitly build objects as .init.o when all
   functions and data within a file are annotated with __init/__initdata,
   ensuring their memory is reclaimed after system initialization.
 - Add an error log in the CPU-to-node mapping function for out-of-bounds
   cases.
 - Use ARRAY_SIZE() instead of raw macros when guarding array accesses.
 - Rename variables and functions to avoid ambiguous or misleading terms:
   - Avoid 'cpuid' to prevent confusion with x86 CPUID features/instructions.
   - Avoid 'node' where it could be confused with a NUMA node, explicitly
     renaming them to clarify they refer to a Device Tree node.
 - Move local variable declarations into the narrowest possible scope.
 - Replace the unsupported "%pOF" printk format specifier with "%s" and
   explicit node name retrieval.
 - Remove #include <dt-cpu-topology.h> from cpu-topology.h, and ensure
   the header directly includes only what its definitions require.
 - Remove #include <xen/device_tree.h> from dt-cpu-topology.h, replacing
   it with a forward declaration of 'struct dt_device_node'.
 - Use 'const' qualifiers for pointer declarations where the pointed-to
   structure is not modified.
 - Explicitly #include <asm/processor.h> in cpu-topology.h to guarantee
   that arch-specific definitions of cpu_to_core() and cpu_to_socket()
   take precedence over the generic fallbacks.
 - Introduce inline initialization functions for cpu_sibling_mask and
   cpu_core_mask in cpu-topology.h, providing separate variants for both
   when CONFIG_GENERIC_CPU_TOPOLOGY is enabled and disabled.

Changes in v3:
 - Use (nr_cpu_ids - 1) as the maximum CPU ID here. The fix for the sparse
   map mismatch issue on ARM Xen has been split out into a separate patch.
 - Switch topology sibling masks to cpumask_var_t for dynamic allocation.
 - Allow the system to keep running with a degraded fallback even if
   the topology table allocation fails.
 - Remove the temporary definitions of cpu_to_core() and cpu_to_socket()
   from RISC-V and PPC processor.h.
 - Minimize the use of #ifdef blocks, leveraging compiler Dead Code
   Elimination (DCE) where possible.
 - Clean up the code to follow the Xen coding style. Please let me know
   if I missed any style nits!
 - Verify successful builds across x86, RISC-V, and PPC environments.

Changes in v2:
 - Generate topology information even when ACPI is enabled. Note that
   this is a temporary implementation and doesn't yet parse the PPTT
   (Processor Properties Topology Table).
 - Added support for cpu-map node in Device Tree that doesn't contain
   explicit cluster node definitions.

Changes in v1 from the previous series "Introduce Device Tree based NUMA
support for ARM Xen":

1. Optimized Memory Allocation:
   The series now allocates only the minimum required memory area to manage
   the essential data for the CPUs.

2. Flexible Device Tree Parsing:
   The parsing logic no longer depends on the definition order of the 'cpu'
   nodes and 'cpu-map' nodes in the Device Tree. They can now be read
   correctly even if their orders do not match.

3. CPU Hotplug Readiness:
   To support future CPU hotplug, the system assumes that inactive CPUs are
   also described in the Device Tree. Xen will pre-load and generate the
   topology information for these inactive CPUs during the boot phase so
   it stays available in memory.

Thank you,
Hirokazu Takahashi

Hirokazu Takahashi (3):
  xen/device-tree: Parse 'cpu-map' node for CPU topology exploration
  xen/sched: Link CPU topology to scheduler
  xen/sched: Make cpu_nr_siblings() architecture-specific

 xen/arch/arm/Kconfig                   |   1 +
 xen/arch/arm/include/asm/processor.h   |   4 -
 xen/arch/arm/smpboot.c                 |  15 +-
 xen/arch/ppc/include/asm/processor.h   |   4 -
 xen/arch/riscv/include/asm/processor.h |   4 -
 xen/arch/x86/include/asm/processor.h   |   1 +
 xen/common/Kconfig                     |  18 ++
 xen/common/Makefile                    |   1 +
 xen/common/cpu-topology.c              |  62 ++++
 xen/common/device-tree/Makefile        |   1 +
 xen/common/device-tree/cpu-topology.c  | 406 +++++++++++++++++++++++++
 xen/common/sched/credit2.c             |  21 +-
 xen/common/sysctl.c                    |   1 +
 xen/drivers/acpi/Kconfig               |   3 +
 xen/drivers/acpi/Makefile              |   1 +
 xen/drivers/acpi/topology.c            |  41 +++
 xen/include/xen/acpi.h                 |   2 +
 xen/include/xen/cpu-topology.h         |  83 +++++
 xen/include/xen/dt-cpu-topology.h      |  29 ++
 19 files changed, 662 insertions(+), 36 deletions(-)
 create mode 100644 xen/common/cpu-topology.c
 create mode 100644 xen/common/device-tree/cpu-topology.c
 create mode 100644 xen/drivers/acpi/topology.c
 create mode 100644 xen/include/xen/cpu-topology.h
 create mode 100644 xen/include/xen/dt-cpu-topology.h

-- 
2.43.0