[PATCH v7 0/7] Unify CPU topology across ARM & RISC-V

Atish Patra atish.patra at wdc.com
Mon Jun 17 11:59:13 PDT 2019

The cpu-map DT entry in ARM can describe the CPU topology in much better
way compared to other existing approaches. RISC-V can easily adopt this
binding to represent its own CPU topology. Thus, both cpu-map DT
binding and topology parsing code can be moved to a common location so
that RISC-V or any other architecture can leverage that.

The relevant discussion regarding unifying cpu topology can be found in

arch_topology seems to be a perfect place to move the common code. I
have not introduced any significant functional changes in the moved code.
The only downside in this approach is that the capacity code will be
executed for RISC-V as well. But, it will exit immediately after not
able to find the appropriate DT node. If the overhead is considered too
much, we can always compile out capacity related functions under a
different config for the architectures that do not support them.

There was an opportunity to unify topology data structure for ARM32 done
by patch 3/4. But, I refrained from making any other changes as I am not
very well versed with original intention for some functions that
are present in arch_topology.c. I hope this patch series can be served
as a baseline for such changes in the future.

The patches have been tested for RISC-V and compile tested for ARM64,
ARM32 & x86.

>From Jeremy,

"I applied these to 5.2rc2, along with my PPTT/MT change and verified the 
system & scheduler topology/etc on DAWN and ThunderX2 using ACPI on arm64.
They appear to be working correctly.

so for the series,
Tested-by: Jeremy Linton <jeremy.linton at arm.com>"

The socket change[2] is also now part of this series.

[1] https://lkml.org/lkml/2018/11/6/19
[2] https://lkml.org/lkml/2018/11/7/918

QEMU changes for RISC-V topology are available at


HiFive Unleashed DT with topology node is available here.

It can be verified with OpenSBI with following additional compile time


Changes from v6->v7
1. Added socket to HiFive Unleashed topology example.
2. Added Acked-by & Reviewed-by.

Changes from v5->v6
1. Added two more patches from Sudeep about maintainership of arch_topology.c
   and Kconfig update.
2. Added Tested-by & Reviewed-by
3. Fixed a nit (reordering of variables)

Changes from v4-v5
1. Removed the arch_topology.h header inclusion from topology.c and arch_topology.c
file. Added it in linux/topology.h.
2. core_id is set to -1 upon reset. Otherwise, ARM topology store function does not

Changes from v3->v4
1. Get rid of ARM32 specific information in topology structure.
2. Remove redundant functions from ARM32 and use common code instead. 

Changes from v2->v3
1. Cover letter update with experiment DT for topology changes.
2. Added the patch for [2].

Changes from v1->v2
1. ARM32 can now use the common code as well.

Atish Patra (4):
dt-binding: cpu-topology: Move cpu-map to a common binding.
cpu-topology: Move cpu topology code to common code.
arm: Use common cpu_topology structure and functions.
RISC-V: Parse cpu topology during boot.

Sudeep Holla (3):
Documentation: DT: arm: add support for sockets defining package
base: arch_topology: update Kconfig help description
MAINTAINERS: Add an entry for generic architecture topology

.../topology.txt => cpu/cpu-topology.txt}     | 136 ++++++--
MAINTAINERS                                   |   7 +
arch/arm/include/asm/topology.h               |  20 --
arch/arm/kernel/topology.c                    |  60 +---
arch/arm64/include/asm/topology.h             |  23 --
arch/arm64/kernel/topology.c                  | 303 +-----------------
arch/riscv/Kconfig                            |   1 +
arch/riscv/kernel/smpboot.c                   |   3 +
drivers/base/Kconfig                          |   2 +-
drivers/base/arch_topology.c                  | 298 +++++++++++++++++
include/linux/arch_topology.h                 |  26 ++
include/linux/topology.h                      |   1 +
12 files changed, 454 insertions(+), 426 deletions(-)
rename Documentation/devicetree/bindings/{arm/topology.txt => cpu/cpu-topology.txt} (66%)


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