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ReStructuredText
ARM SiP Service
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===============
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This document enumerates and describes the ARM SiP (Silicon Provider) services.
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SiP services are non-standard, platform-specific services offered by the silicon
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implementer or platform provider. They are accessed via. ``SMC`` ("SMC calls")
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instruction executed from Exception Levels below EL3. SMC calls for SiP
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services:
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- Follow `SMC Calling Convention`_;
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- Use SMC function IDs that fall in the SiP range, which are ``0xc2000000`` -
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``0xc200ffff`` for 64-bit calls, and ``0x82000000`` - ``0x8200ffff`` for 32-bit
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calls.
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The ARM SiP implementation offers the following services:
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- Performance Measurement Framework (PMF)
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- Execution State Switching service
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Source definitions for ARM SiP service are located in the ``arm_sip_svc.h`` header
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file.
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Performance Measurement Framework (PMF)
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---------------------------------------
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The `Performance Measurement Framework`_
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allows callers to retrieve timestamps captured at various paths in ARM Trusted
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Firmware execution. It's described in detail in `Firmware Design document`_.
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Execution State Switching service
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---------------------------------
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Execution State Switching service provides a mechanism for a non-secure lower
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Exception Level (either EL2, or NS EL1 if EL2 isn't implemented) to request to
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switch its execution state (a.k.a. Register Width), either from AArch64 to
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AArch32, or from AArch32 to AArch64, for the calling CPU. This service is only
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available when ARM Trusted Firmware is built for AArch64 (i.e. when build option
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``ARCH`` is set to ``aarch64``).
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``ARM_SIP_SVC_EXE_STATE_SWITCH``
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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::
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Arguments:
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uint32_t Function ID
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uint32_t PC hi
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uint32_t PC lo
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uint32_t Cookie hi
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uint32_t Cookie lo
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Return:
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uint32_t
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The function ID parameter must be ``0x82000020``. It uniquely identifies the
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Execution State Switching service being requested.
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The parameters *PC hi* and *PC lo* defines upper and lower words, respectively,
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of the entry point (physical address) at which execution should start, after
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Execution State has been switched. When calling from AArch64, *PC hi* must be 0.
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When execution starts at the supplied entry point after Execution State has been
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switched, the parameters *Cookie hi* and *Cookie lo* are passed in CPU registers
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0 and 1, respectively. When calling from AArch64, *Cookie hi* must be 0.
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This call can only be made on the primary CPU, before any secondaries were
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brought up with ``CPU_ON`` PSCI call. Otherwise, the call will always fail.
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The effect of switching execution state is as if the Exception Level were
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entered for the first time, following power on. This means CPU registers that
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have a defined reset value by the Architecture will assume that value. Other
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registers should not be expected to hold their values before the call was made.
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CPU endianness, however, is preserved from the previous execution state. Note
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that this switches the execution state of the calling CPU only. This is not a
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substitute for PSCI ``SYSTEM_RESET``.
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The service may return the following error codes:
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- ``STATE_SW_E_PARAM``: If any of the parameters were deemed invalid for
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a specific request.
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- ``STATE_SW_E_DENIED``: If the call is not successful, or when ARM Trusted
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Firmware is built for AArch32.
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If the call is successful, the caller wouldn't observe the SMC returning.
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Instead, execution starts at the supplied entry point, with the CPU registers 0
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and 1 populated with the supplied *Cookie hi* and *Cookie lo* values,
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respectively.
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--------------
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*Copyright (c) 2017, ARM Limited and Contributors. All rights reserved.*
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.. _SMC Calling Convention: http://infocenter.arm.com/help/topic/com.arm.doc.den0028a/index.html
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.. _Performance Measurement Framework: ./firmware-design.rst#user-content-performance-measurement-framework
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.. _Firmware Design document: ./firmware-design.rst
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