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diff --git a/roms/skiboot/doc/device-tree/ibm,powerpc-cpu-features/binding.rst b/roms/skiboot/doc/device-tree/ibm,powerpc-cpu-features/binding.rst new file mode 100644 index 000000000..703823047 --- /dev/null +++ b/roms/skiboot/doc/device-tree/ibm,powerpc-cpu-features/binding.rst @@ -0,0 +1,302 @@ +ibm,powerpc-cpu-features Binding +================================ + +This device tree binding describes CPU features available to software, with +enablement, privilege, and compatibility metadata. + +More general description of design and implementation of this binding is +found in design.txt, which also points to documentation of specific features. + + +/cpus/ibm,powerpc-cpu-features node binding +------------------------------------------- + +Node: ibm,powerpc-cpu-features + +Description: Container of CPU feature nodes. + +The node name must be "ibm,powerpc-cpu-features". + +It is implemented as a child of the node "/cpus", but this must not be +assumed by parsers. + +The node is optional but should be provided by new OPAL firmware. + +Properties: + +- device_type + + Usage: + required + Value type: + string + Definition: + "cpu-features" + +- compatible + + Usage: + required + Value type: + string + Definition: + "ibm,powerpc-cpu-features" + + This compatibility refers to backwards compatibility of the overall + design with parsers that behave according to these guidelines. This can + be extended in a backward compatible manner which would not warrant a + revision of the compatible property. + +- isa + + Usage: + required + Value type: + <u32> + + Definition: + + isa that the CPU is currently running in. This provides instruction set + compatibility, less the individual feature nodes. For example, an ISA v3.0 + implementation that lacks the "transactional-memory" cpufeature node + should not use transactional memory facilities. + + Value corresponds to the "Power ISA Version" multiplied by 1000. + For example, <3000> corresponds to Version 3.0, <2070> to Version 2.07. + The minor digit is available for revisions. + +/cpus/ibm,powerpc-cpu-features/example-feature node bindings +---------------------------------------------------------------- + +Each child node of cpu-features represents a CPU feature / capability. + +Node: A string describing an architected CPU feature, e.g., "floating-point". + +Description: A feature or capability supported by the CPUs. + +The name of the node is a human readable string that forms the interface +used to describe features to software. Features are currently documented +in the code where they are implemented in skiboot/core/cpufeatures.c + +Presence of the node indicates the feature is available. + +Properties: + +- isa + + Usage: + required + Value type: + <u32> + + Definition: + + First level of the Power ISA that the feature appears in. + Software should filter out features when constraining the + environment to a particular ISA version. + + Value is defined similarly to /cpus/features/isa + +- usable-privilege + + Usage: + required + Value type: + <u32> bit mask + Definition: + Bit numbers are LSB0 + + bit 0: + PR (problem state / user mode) + bit 1: + OS (privileged state) + bit 2: + HV (hypervisor state) + + All other bits reserved and should be zero. + + This property describes the privilege levels and/or software components + that can use the feature. + + If bit 0 is set, then the hwcap-bit-nr property will exist. + + +- hv-support + + Usage: + optional + Value type: + <u32> bit mask + Definition: + Bit numbers are LSB0 + + bit 0: + HFSCR + + All other bits reserved and should be zero. + + This property describes the HV privilege support required to enable the + feature to lesser privilege levels. If the property does not exist then no + support is required. + + If no bits are set, the hypervisor must have explicit/custom support for + this feature. + + If the HFSCR bit is set, then the hfscr-bit-nr property will exist and + the feature may be enabled by setting this bit in the HFSCR register. + + +- os-support + + Usage: + optional + Value type: + <u32> bit mask + Definition: + Bit numbers are LSB0 + + bit 0: + FSCR + + All other bits reserved and should be zero. + + This property describes the OS privilege support required to enable the + feature to lesser privilege levels. If the property does not exist then no + support is required. + + If no bits are set, the operating system must have explicit/custom support + for this feature. + + If the FSCR bit is set, then the fscr-bit-nr property will exist and + the feature may be enabled by setting this bit in the FSCR register. + + +- hfscr-bit-nr + + Usage: + optional + Value type: + <u32> + Definition: + HFSCR bit position (LSB0) + + This property exists when the hv-support property HFSCR bit is set. This + property describes the bit number in the HFSCR register that the + hypervisor must set in order to enable this feature. + + This property also exists if an HFSCR bit corresponds with this feature. + This makes CPU feature parsing slightly simpler. + + +- fscr-bit-nr + + Usage: + optional + Value type: + <u32> + Definition: + FSCR bit position (LSB0) + + This property exists when the os-support property FSCR bit is set. This + property describes the bit number in the FSCR register that the + operating system must set in order to enable this feature. + + This property also exists if an FSCR bit corresponds with this feature. + This makes CPU feature parsing slightly simpler. + + +- hwcap-bit-nr + + Usage: + optional + Value type: + <u32> + Definition: + Linux ELF AUX vector bit position (LSB0) + + This property may exist when the usable-privilege property value has PR bit set. + This property describes the bit number that should be set in the ELF AUX + hardware capability vectors in order to advertise this feature to userspace. + Bits 0-31 correspond to bits 0-31 in AT_HWCAP vector. Bits 32-63 correspond + to 0-31 in AT_HWCAP2 vector, and so on. Missing AT_HWCAPx vectors implies + that the feature is not enabled or can not be advertised. Operating systems + may provide a number of unassigned hardware capability bits to allow for new + features to be advertised. + + Some properties representing features created before this binding are + advertised to userspace without a one-to-one hwcap bit number may not specify + this bit. Operating system will handle those bits specifically. All new + features usable by userspace will have a hwcap-bit-nr property. + + +- dependencies + + Usage: + optional + Value type: + <prop-encoded-array> + + Definition: + + If this property exists then it is a list of phandles to cpu feature + nodes that must be enabled for this feature to be enabled. + + +- Custom properties of the feature + + Usage: + optional + + Definition: + + Particular features may define their own properties. + + +Example +------- + +.. code-block:: dts + + /cpus/ibm,powerpc-cpu-features { + device_type = "ibm,powerpc-cpu-features"; + + isa = <3020>; + + darn { + isa = <3000>; + usable-privilege = <1 | 2 | 4>; + hwcap-bit-nr = <xx>; + }; + + scv { + isa = <3000>; + usable-privilege = <1 | 2>; + os-support = <0>; + hwcap-bit-nr = <xx>; + }; + + stop { + isa = <3000>; + usable-privilege = <2 | 4>; + hv-support = <0>; + os-support = <0>; + }; + + vsx2 (hypothetical) { + isa = <3010>; + usable-privilege = <1 | 2 | 4>; + hv-support = <0>; + os-support = <0>; + hwcap-bit-nr = <xx>; + }; + + vsx2-newinsns { + isa = <3020>; + usable-privilege = <1 | 2 | 4>; + os-support = <1>; + fscr-bit-nr = <xx>; + hwcap-bit-nr = <xx>; + dependencies = <&vsx2>; + }; + + }; |