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+Arm CPU Specific Build Macros
+=============================
+
+
+
+
+.. contents::
+
+This document describes the various build options present in the CPU specific
+operations framework to enable errata workarounds and to enable optimizations
+for a specific CPU on a platform.
+
+Security Vulnerability Workarounds
+----------------------------------
+
+TF-A exports a series of build flags which control which security
+vulnerability workarounds should be applied at runtime.
+
+-  ``WORKAROUND_CVE_2017_5715``: Enables the security workaround for
+   `CVE-2017-5715`_. This flag can be set to 0 by the platform if none
+   of the PEs in the system need the workaround. Setting this flag to 0 provides
+   no performance benefit for non-affected platforms, it just helps to comply
+   with the recommendation in the spec regarding workaround discovery.
+   Defaults to 1.
+
+-  ``WORKAROUND_CVE_2018_3639``: Enables the security workaround for
+   `CVE-2018-3639`_. Defaults to 1. The TF-A project recommends to keep
+   the default value of 1 even on platforms that are unaffected by
+   CVE-2018-3639, in order to comply with the recommendation in the spec
+   regarding workaround discovery.
+
+-  ``DYNAMIC_WORKAROUND_CVE_2018_3639``: Enables dynamic mitigation for
+   `CVE-2018-3639`_. This build option should be set to 1 if the target
+   platform contains at least 1 CPU that requires dynamic mitigation.
+   Defaults to 0.
+
+CPU Errata Workarounds
+----------------------
+
+TF-A exports a series of build flags which control the errata workarounds that
+are applied to each CPU by the reset handler. The errata details can be found
+in the CPU specific errata documents published by Arm:
+
+-  `Cortex-A53 MPCore Software Developers Errata Notice`_
+-  `Cortex-A57 MPCore Software Developers Errata Notice`_
+-  `Cortex-A72 MPCore Software Developers Errata Notice`_
+
+The errata workarounds are implemented for a particular revision or a set of
+processor revisions. This is checked by the reset handler at runtime. Each
+errata workaround is identified by its ``ID`` as specified in the processor's
+errata notice document. The format of the define used to enable/disable the
+errata workaround is ``ERRATA_<Processor name>_<ID>``, where the ``Processor name``
+is for example ``A57`` for the ``Cortex_A57`` CPU.
+
+Refer to the section *CPU errata status reporting* in
+`Firmware Design guide`_ for information on how to write errata workaround
+functions.
+
+All workarounds are disabled by default. The platform is responsible for
+enabling these workarounds according to its requirement by defining the
+errata workaround build flags in the platform specific makefile. In case
+these workarounds are enabled for the wrong CPU revision then the errata
+workaround is not applied. In the DEBUG build, this is indicated by
+printing a warning to the crash console.
+
+In the current implementation, a platform which has more than 1 variant
+with different revisions of a processor has no runtime mechanism available
+for it to specify which errata workarounds should be enabled or not.
+
+The value of the build flags is 0 by default, that is, disabled. A value of 1
+will enable it.
+
+For Cortex-A9, the following errata build flags are defined :
+
+-  ``ERRATA_A9_794073``: This applies errata 794073 workaround to Cortex-A9
+   CPU. This needs to be enabled for all revisions of the CPU.
+
+For Cortex-A15, the following errata build flags are defined :
+
+-  ``ERRATA_A15_816470``: This applies errata 816470 workaround to Cortex-A15
+   CPU. This needs to be enabled only for revision >= r3p0 of the CPU.
+
+-  ``ERRATA_A15_827671``: This applies errata 827671 workaround to Cortex-A15
+   CPU. This needs to be enabled only for revision >= r3p0 of the CPU.
+
+For Cortex-A17, the following errata build flags are defined :
+
+-  ``ERRATA_A17_852421``: This applies errata 852421 workaround to Cortex-A17
+   CPU. This needs to be enabled only for revision <= r1p2 of the CPU.
+
+-  ``ERRATA_A17_852423``: This applies errata 852423 workaround to Cortex-A17
+   CPU. This needs to be enabled only for revision <= r1p2 of the CPU.
+
+For Cortex-A35, the following errata build flags are defined :
+
+-  ``ERRATA_A35_855472``: This applies errata 855472 workaround to Cortex-A35
+   CPUs. This needs to be enabled only for revision r0p0 of Cortex-A35.
+
+For Cortex-A53, the following errata build flags are defined :
+
+-  ``ERRATA_A53_819472``: This applies errata 819472 workaround to all
+   CPUs. This needs to be enabled only for revision <= r0p1 of Cortex-A53.
+
+-  ``ERRATA_A53_824069``: This applies errata 824069 workaround to all
+   CPUs. This needs to be enabled only for revision <= r0p2 of Cortex-A53.
+
+-  ``ERRATA_A53_826319``: This applies errata 826319 workaround to Cortex-A53
+   CPU. This needs to be enabled only for revision <= r0p2 of the CPU.
+
+-  ``ERRATA_A53_827319``: This applies errata 827319 workaround to all
+   CPUs. This needs to be enabled only for revision <= r0p2 of Cortex-A53.
+
+-  ``ERRATA_A53_835769``: This applies erratum 835769 workaround at compile and
+   link time to Cortex-A53 CPU. This needs to be enabled for some variants of
+   revision <= r0p4. This workaround can lead the linker to create ``*.stub``
+   sections.
+
+-  ``ERRATA_A53_836870``: This applies errata 836870 workaround to Cortex-A53
+   CPU. This needs to be enabled only for revision <= r0p3 of the CPU. From
+   r0p4 and onwards, this errata is enabled by default in hardware.
+
+-  ``ERRATA_A53_843419``: This applies erratum 843419 workaround at link time
+   to Cortex-A53 CPU.  This needs to be enabled for some variants of revision
+   <= r0p4. This workaround can lead the linker to emit ``*.stub`` sections
+   which are 4kB aligned.
+
+-  ``ERRATA_A53_855873``: This applies errata 855873 workaround to Cortex-A53
+   CPUs. Though the erratum is present in every revision of the CPU,
+   this workaround is only applied to CPUs from r0p3 onwards, which feature
+   a chicken bit in CPUACTLR_EL1 to enable a hardware workaround.
+   Earlier revisions of the CPU have other errata which require the same
+   workaround in software, so they should be covered anyway.
+
+For Cortex-A55, the following errata build flags are defined :
+
+-  ``ERRATA_A55_768277``: This applies errata 768277 workaround to Cortex-A55
+   CPU. This needs to be enabled only for revision r0p0 of the CPU.
+
+-  ``ERRATA_A55_778703``: This applies errata 778703 workaround to Cortex-A55
+   CPU. This needs to be enabled only for revision r0p0 of the CPU.
+
+-  ``ERRATA_A55_798797``: This applies errata 798797 workaround to Cortex-A55
+   CPU. This needs to be enabled only for revision r0p0 of the CPU.
+
+-  ``ERRATA_A55_846532``: This applies errata 846532 workaround to Cortex-A55
+   CPU. This needs to be enabled only for revision <= r0p1 of the CPU.
+
+-  ``ERRATA_A55_903758``: This applies errata 903758 workaround to Cortex-A55
+   CPU. This needs to be enabled only for revision <= r0p1 of the CPU.
+
+For Cortex-A57, the following errata build flags are defined :
+
+-  ``ERRATA_A57_806969``: This applies errata 806969 workaround to Cortex-A57
+   CPU. This needs to be enabled only for revision r0p0 of the CPU.
+
+-  ``ERRATA_A57_813419``: This applies errata 813419 workaround to Cortex-A57
+   CPU. This needs to be enabled only for revision r0p0 of the CPU.
+
+-  ``ERRATA_A57_813420``: This applies errata 813420 workaround to Cortex-A57
+   CPU. This needs to be enabled only for revision r0p0 of the CPU.
+
+-  ``ERRATA_A57_814670``: This applies errata 814670 workaround to Cortex-A57
+   CPU. This needs to be enabled only for revision r0p0 of the CPU.
+
+-  ``ERRATA_A57_817169``: This applies errata 817169 workaround to Cortex-A57
+   CPU. This needs to be enabled only for revision <= r0p1 of the CPU.
+
+-  ``ERRATA_A57_826974``: This applies errata 826974 workaround to Cortex-A57
+   CPU. This needs to be enabled only for revision <= r1p1 of the CPU.
+
+-  ``ERRATA_A57_826977``: This applies errata 826977 workaround to Cortex-A57
+   CPU. This needs to be enabled only for revision <= r1p1 of the CPU.
+
+-  ``ERRATA_A57_828024``: This applies errata 828024 workaround to Cortex-A57
+   CPU. This needs to be enabled only for revision <= r1p1 of the CPU.
+
+-  ``ERRATA_A57_829520``: This applies errata 829520 workaround to Cortex-A57
+   CPU. This needs to be enabled only for revision <= r1p2 of the CPU.
+
+-  ``ERRATA_A57_833471``: This applies errata 833471 workaround to Cortex-A57
+   CPU. This needs to be enabled only for revision <= r1p2 of the CPU.
+
+-  ``ERRATA_A57_859972``: This applies errata 859972 workaround to Cortex-A57
+   CPU. This needs to be enabled only for revision <= r1p3 of the CPU.
+
+
+For Cortex-A72, the following errata build flags are defined :
+
+-  ``ERRATA_A72_859971``: This applies errata 859971 workaround to Cortex-A72
+   CPU. This needs to be enabled only for revision <= r0p3 of the CPU.
+
+For Cortex-A73, the following errata build flags are defined :
+
+-  ``ERRATA_A73_852427``: This applies errata 852427 workaround to Cortex-A73
+   CPU. This needs to be enabled only for revision r0p0 of the CPU.
+
+-  ``ERRATA_A73_855423``: This applies errata 855423 workaround to Cortex-A73
+   CPU. This needs to be enabled only for revision <= r0p1 of the CPU.
+
+For Cortex-A75, the following errata build flags are defined :
+
+-  ``ERRATA_A75_764081``: This applies errata 764081 workaround to Cortex-A75
+   CPU. This needs to be enabled only for revision r0p0 of the CPU.
+
+-  ``ERRATA_A75_790748``: This applies errata 790748 workaround to Cortex-A75
+    CPU. This needs to be enabled only for revision r0p0 of the CPU.
+
+For Cortex-A76, the following errata build flags are defined :
+
+-  ``ERRATA_A76_1073348``: This applies errata 1073348 workaround to Cortex-A76
+   CPU. This needs to be enabled only for revision <= r1p0 of the CPU.
+
+-  ``ERRATA_A76_1130799``: This applies errata 1130799 workaround to Cortex-A76
+   CPU. This needs to be enabled only for revision <= r2p0 of the CPU.
+
+-  ``ERRATA_A76_1220197``: This applies errata 1220197 workaround to Cortex-A76
+   CPU. This needs to be enabled only for revision <= r2p0 of the CPU.
+
+-  ``ERRATA_A76_1257314``: This applies errata 1257314 workaround to Cortex-A76
+   CPU. This needs to be enabled only for revision <= r3p0 of the CPU.
+
+-  ``ERRATA_A76_1262606``: This applies errata 1262606 workaround to Cortex-A76
+   CPU. This needs to be enabled only for revision <= r3p0 of the CPU.
+
+-  ``ERRATA_A76_1262888``: This applies errata 1262888 workaround to Cortex-A76
+   CPU. This needs to be enabled only for revision <= r3p0 of the CPU.
+
+-  ``ERRATA_A76_1275112``: This applies errata 1275112 workaround to Cortex-A76
+   CPU. This needs to be enabled only for revision <= r3p0 of the CPU.
+
+DSU Errata Workarounds
+----------------------
+
+Similar to CPU errata, TF-A also implements workarounds for DSU (DynamIQ
+Shared Unit) errata. The DSU errata details can be found in the respective Arm
+documentation:
+
+- `Arm DSU Software Developers Errata Notice`_.
+
+Each erratum is identified by an ``ID``, as defined in the DSU errata notice
+document. Thus, the build flags which enable/disable the errata workarounds
+have the format ``ERRATA_DSU_<ID>``. The implementation and application logic
+of DSU errata workarounds are similar to `CPU errata workarounds`_.
+
+For DSU errata, the following build flags are defined:
+
+-  ``ERRATA_DSU_798953``: This applies errata 798953 workaround for the
+   affected DSU configurations. This errata applies only for those DSUs that
+   revision is r0p0 (on r0p1 it is fixed). However, please note that this
+   workaround results in increased DSU power consumption on idle.
+
+-  ``ERRATA_DSU_936184``: This applies errata 936184 workaround for the
+   affected DSU configurations. This errata applies only for those DSUs that
+   contain the ACP interface **and** the DSU revision is older than r2p0 (on
+   r2p0 it is fixed). However, please note that this workaround results in
+   increased DSU power consumption on idle.
+
+CPU Specific optimizations
+--------------------------
+
+This section describes some of the optimizations allowed by the CPU micro
+architecture that can be enabled by the platform as desired.
+
+-  ``SKIP_A57_L1_FLUSH_PWR_DWN``: This flag enables an optimization in the
+   Cortex-A57 cluster power down sequence by not flushing the Level 1 data
+   cache. The L1 data cache and the L2 unified cache are inclusive. A flush
+   of the L2 by set/way flushes any dirty lines from the L1 as well. This
+   is a known safe deviation from the Cortex-A57 TRM defined power down
+   sequence. Each Cortex-A57 based platform must make its own decision on
+   whether to use the optimization.
+
+-  ``A53_DISABLE_NON_TEMPORAL_HINT``: This flag disables the cache non-temporal
+   hint. The LDNP/STNP instructions as implemented on Cortex-A53 do not behave
+   in a way most programmers expect, and will most probably result in a
+   significant speed degradation to any code that employs them. The Armv8-A
+   architecture (see Arm DDI 0487A.h, section D3.4.3) allows cores to ignore
+   the non-temporal hint and treat LDNP/STNP as LDP/STP instead. Enabling this
+   flag enforces this behaviour. This needs to be enabled only for revisions
+   <= r0p3 of the CPU and is enabled by default.
+
+-  ``A57_DISABLE_NON_TEMPORAL_HINT``: This flag has the same behaviour as
+   ``A53_DISABLE_NON_TEMPORAL_HINT`` but for Cortex-A57. This needs to be
+   enabled only for revisions <= r1p2 of the CPU and is enabled by default,
+   as recommended in section "4.7 Non-Temporal Loads/Stores" of the
+   `Cortex-A57 Software Optimization Guide`_.
+
+--------------
+
+*Copyright (c) 2014-2019, Arm Limited and Contributors. All rights reserved.*
+
+.. _CVE-2017-5715: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-5715
+.. _CVE-2018-3639: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-3639
+.. _Cortex-A53 MPCore Software Developers Errata Notice: http://infocenter.arm.com/help/topic/com.arm.doc.epm048406/index.html
+.. _Cortex-A57 MPCore Software Developers Errata Notice: http://infocenter.arm.com/help/topic/com.arm.doc.epm049219/index.html
+.. _Cortex-A72 MPCore Software Developers Errata Notice: http://infocenter.arm.com/help/topic/com.arm.doc.epm012079/index.html
+.. _Firmware Design guide: firmware-design.rst
+.. _Cortex-A57 Software Optimization Guide: http://infocenter.arm.com/help/topic/com.arm.doc.uan0015b/Cortex_A57_Software_Optimization_Guide_external.pdf
+.. _Arm DSU Software Developers Errata Notice: http://infocenter.arm.com/help/topic/com.arm.doc.epm138168/index.html