RFC ARM: introducing DT topology
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1 of 5 patches is in this archive. The cover letter announces 5.
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| # | Subject and files | Size | Replies | Applied |
|---|---|---|---|---|
| 4/5 | ARM: gic: add cpuif topology description | +0 | 1 reply |
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Cover letter [RFC PATCH 0/5] ARM: introducing DT topology
Quoted 13 lines · Lorenzo Pieralisi
The introduction of multi-cluster ARM systems in SoC designs requires the kernel to become cluster aware, so that it can be booted on every CPU in the system and it can build an appropriate representation of topology levels.
Current code in the kernel, in particular the boot sequence, hinges upon a sequential mapping of MPIDR values for cpus and related interrupt controller CPU interfaces to logical cpu indexing.
This hypothesis is not valid when the concept of cluster is introduced since the MPIDR cannot be represented as a single index and interrupt controller CPU interfaces might be wired with a numbering scheme following per-SoC design parameters which cannot be extrapolated easily through generic functions by the primary CPU.
Quoted 4 lines
Furthermore, relying on the MPIDR to be wired according to real topology levels might turn out to be an unreliable solution, hence a SW representation is needed to override possibly incorrect MPIDR register values.
"might be" is used several times. Is this a real problem? Wouldn't a more simple solution be providing properties to override the MPIDR register value if it is unreliable?
Quoted 42 lines
Through the device tree and relative bindings, the kernel is provided with HW values for MPIDR registers, interrupt controller CPU interfaces and with a topology representation of hierarchy levels and connection between cores.
The device tree bindings allow to boot the Linux kernel on a multi-cluster system without relying on platform specific hook to identify the number of CPUs and interrupt controller wiring definition.
The patchset has been tested against:
git://git.kernel.org/pub/scm/linux/kernel/git/cmarinas/linux-arm-arch.gitmasterto boot an 8-core dual-cluster system on every possible CPU and to describe the relative cpu topology according to the affinity levels.
Compile tested against linux-next, with a dependency on the following patch:
http://www.spinics.net/lists/arm-kernel/msg155873.html
Documentation of new device tree bindings is provided in the corresponding patches and provided for discussion.
Lorenzo Pieralisi (5):
ARM: kernel: add device tree init map function
ARM: kernel: add cpu logical map DT init insetup_arch
ARM: kernel: add logical mappings look-up
ARM: gic: add cpuif topology description
ARM: kernel: build CPU topology from DTDocumentation/devicetree/bindings/arm/cpus.txt | 42 +++++ Documentation/devicetree/bindings/arm/gic.txt | 69 ++++++++ Documentation/devicetree/bindings/arm/topology.txt | 167 ++++++++++++++++++++ arch/arm/common/gic.c | 94 +++++++++++- arch/arm/include/asm/prom.h | 2 + arch/arm/include/asm/smp_plat.h | 12 ++ arch/arm/kernel/devtree.c | 40 +++++ arch/arm/kernel/setup.c | 1 + arch/arm/kernel/topology.c | 110 +++++++++++--- 9 files changed, 513 insertions(+), 24 deletions(-) create mode 100644 Documentation/devicetree/bindings/arm/cpus.txt create mode 100644 Documentation/devicetree/bindings/arm/topology.txt