On Tue, Apr 22, 2025 at 3:43 AM Alireza Sanaee
<alireza.sanaee@huawei.com> wrote:
>
> This patchset allows for sharing resources between SMT threads in the
> device tree (DT).
>
> WHY? Given the current use of the DT, it is not possible to share L1
> caches, as well as other resources such as clock among SMT threads.
> However, DT spec in section Section 3.8.1 [1], describes how SMT threads
> can be described in the reg array, this is how PowerPC describes SMT
> threads in DT.
>
> CHALLENGE: Given discussions with the community [2], it was apparent
> that it is not straightforward to implement this, since cpu-maps must
> point to a particular CPU node in DT [3], Section 2.1. However, it is
> not only the cpu-map but also there other nodes that point to cpu nodes
> which indeed need care and changes.
>
> SOLUTION: This led to more discussions on what the solution should look
> like and based on recent converstations we ended up with the following
> approach [4].
>
> core0 {
> thread0 {
> cpu = <&cpu0 0>;
> };
> thread1 {
> cpu = <&cpu0 1>;
> };
> };
>
> In this layout, first parameter is the phandle to cpu-node and second
> index would be the local-thread index in the reg array available in the
> cpu-node reg property. Further, when reading the property in the cpu-map
> we must know how many parameters phandle has in cpu property. Therefore,
> we optionally introduced "#cpu-cells" property to indicate the number of
> cells.
>
> [1] https://github.com/devicetree-org/devicetree-specification/releases/download/v0.4/devicetree-specification-v0.4.pdf
> [2] https://lore.kernel.org/linux-arm-kernel/Z4FJZPRg75YIUR2l@J2N7QTR9R3/
> [3] https://www.kernel.org/doc/Documentation/devicetree/bindings/cpu/cpu-topology.txt
> [4] https://lore.kernel.org/devicetree-spec/CAL_JsqK1yqRLD9B+G7UUp=D8K++mXHq0Rmv=1i6DL_jXyZwXAw@mail.gmail.com/
>
> Alireza Sanaee (5):
> DT: add infra for finding CPU id from phandle.
> arm64: of: handle multiple threads in ARM cpu node
> driver/base/arch_topology: update CPU map to use the new API.
> driver/hwtracing/coresight: Use of_cpu_phandle_to_id for grabbing CPU
> id.
You kind of have the path, but it's 'drivers' not 'driver'. In any
case, that should be dropped. Use the prefix of the particular
subsystem (git log --oneline path should tell you).
These 2 patches do the same change. Use a consistent subject.
> DT: of_cpu_phandle_to_id to support SMT threads
Patches 1, 3, and 4 are useful refactoring regardless. They should
come first in the series.
> arch/arm64/kernel/smp.c | 74 ++++++++++---------
> drivers/base/arch_topology.c | 12 +--
> .../coresight/coresight-cti-platform.c | 15 +---
> .../hwtracing/coresight/coresight-platform.c | 14 +---
> drivers/of/cpu.c | 45 +++++++++++
> include/linux/of.h | 3 +
> 6 files changed, 100 insertions(+), 63 deletions(-)
>
> --
> 2.43.0
>