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ca6b1cb4dd
Add documentation for errata 835769 and 843419 workarounds introduced in
commit a94cc374ab
Fixes ARM-software/tf-issues#504
Change-Id: I7f3db53dfc5f3827b32663f483d3302bc9679b19
Signed-off-by: Douglas Raillard <douglas.raillard@arm.com>
138 lines
6.7 KiB
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138 lines
6.7 KiB
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ARM CPU Specific Build Macros
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=============================
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.. section-numbering::
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:suffix: .
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.. contents::
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This document describes the various build options present in the CPU specific
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operations framework to enable errata workarounds and to enable optimizations
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for a specific CPU on a platform.
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CPU Errata Workarounds
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----------------------
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ARM Trusted Firmware exports a series of build flags which control the
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errata workarounds that are applied to each CPU by the reset handler. The
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errata details can be found in the CPU specific errata documents published
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by ARM:
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- `Cortex-A53 MPCore Software Developers Errata Notice`_
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- `Cortex-A57 MPCore Software Developers Errata Notice`_
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The errata workarounds are implemented for a particular revision or a set of
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processor revisions. This is checked by the reset handler at runtime. Each
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errata workaround is identified by its ``ID`` as specified in the processor's
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errata notice document. The format of the define used to enable/disable the
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errata workaround is ``ERRATA_<Processor name>_<ID>``, where the ``Processor name``
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is for example ``A57`` for the ``Cortex_A57`` CPU.
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Refer to the section *CPU errata status reporting* in
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`Firmware Design guide`_ for information on to write errata workaround functions.
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All workarounds are disabled by default. The platform is responsible for
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enabling these workarounds according to its requirement by defining the
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errata workaround build flags in the platform specific makefile. In case
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these workarounds are enabled for the wrong CPU revision then the errata
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workaround is not applied. In the DEBUG build, this is indicated by
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printing a warning to the crash console.
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In the current implementation, a platform which has more than 1 variant
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with different revisions of a processor has no runtime mechanism available
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for it to specify which errata workarounds should be enabled or not.
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The value of the build flags are 0 by default, that is, disabled. Any other
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value will enable it.
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For Cortex-A53, following errata build flags are defined :
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- ``ERRATA_A53_826319``: This applies errata 826319 workaround to Cortex-A53
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CPU. This needs to be enabled only for revision <= r0p2 of the CPU.
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- ``ERRATA_A53_835769``: This applies erratum 835769 workaround at compile and
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link time to Cortex-A53 CPU. This needs to be enabled for some variants of
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revision <= r0p4. This workaround can lead the linker to create ``*.stub``
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sections.
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- ``ERRATA_A53_836870``: This applies errata 836870 workaround to Cortex-A53
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CPU. This needs to be enabled only for revision <= r0p3 of the CPU. From
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r0p4 and onwards, this errata is enabled by default in hardware.
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- ``ERRATA_A53_843419``: This applies erratum 843419 workaround at link time
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to Cortex-A53 CPU. This needs to be enabled for some variants of revision
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<= r0p4. This workaround can lead the linker to emit ``*.stub`` sections
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which are 4kB aligned.
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- ``ERRATA_A53_855873``: This applies errata 855873 workaround to Cortex-A53
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CPUs. Though the erratum is present in every revision of the CPU,
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this workaround is only applied to CPUs from r0p3 onwards, which feature
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a chicken bit in CPUACTLR\_EL1 to enable a hardware workaround.
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Earlier revisions of the CPU have other errata which require the same
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workaround in software, so they should be covered anyway.
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For Cortex-A57, following errata build flags are defined :
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- ``ERRATA_A57_806969``: This applies errata 806969 workaround to Cortex-A57
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CPU. This needs to be enabled only for revision r0p0 of the CPU.
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- ``ERRATA_A57_813419``: This applies errata 813419 workaround to Cortex-A57
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CPU. This needs to be enabled only for revision r0p0 of the CPU.
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- ``ERRATA_A57_813420``: This applies errata 813420 workaround to Cortex-A57
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CPU. This needs to be enabled only for revision r0p0 of the CPU.
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- ``ERRATA_A57_826974``: This applies errata 826974 workaround to Cortex-A57
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CPU. This needs to be enabled only for revision <= r1p1 of the CPU.
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- ``ERRATA_A57_826977``: This applies errata 826977 workaround to Cortex-A57
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CPU. This needs to be enabled only for revision <= r1p1 of the CPU.
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- ``ERRATA_A57_828024``: This applies errata 828024 workaround to Cortex-A57
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CPU. This needs to be enabled only for revision <= r1p1 of the CPU.
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- ``ERRATA_A57_829520``: This applies errata 829520 workaround to Cortex-A57
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CPU. This needs to be enabled only for revision <= r1p2 of the CPU.
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- ``ERRATA_A57_833471``: This applies errata 833471 workaround to Cortex-A57
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CPU. This needs to be enabled only for revision <= r1p2 of the CPU.
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CPU Specific optimizations
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--------------------------
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This section describes some of the optimizations allowed by the CPU micro
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architecture that can be enabled by the platform as desired.
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- ``SKIP_A57_L1_FLUSH_PWR_DWN``: This flag enables an optimization in the
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Cortex-A57 cluster power down sequence by not flushing the Level 1 data
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cache. The L1 data cache and the L2 unified cache are inclusive. A flush
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of the L2 by set/way flushes any dirty lines from the L1 as well. This
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is a known safe deviation from the Cortex-A57 TRM defined power down
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sequence. Each Cortex-A57 based platform must make its own decision on
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whether to use the optimization.
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- ``A53_DISABLE_NON_TEMPORAL_HINT``: This flag disables the cache non-temporal
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hint. The LDNP/STNP instructions as implemented on Cortex-A53 do not behave
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in a way most programmers expect, and will most probably result in a
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significant speed degradation to any code that employs them. The ARMv8-A
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architecture (see ARM DDI 0487A.h, section D3.4.3) allows cores to ignore
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the non-temporal hint and treat LDNP/STNP as LDP/STP instead. Enabling this
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flag enforces this behaviour. This needs to be enabled only for revisions
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<= r0p3 of the CPU and is enabled by default.
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- ``A57_DISABLE_NON_TEMPORAL_HINT``: This flag has the same behaviour as
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``A53_DISABLE_NON_TEMPORAL_HINT`` but for Cortex-A57. This needs to be
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enabled only for revisions <= r1p2 of the CPU and is enabled by default,
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as recommended in section "4.7 Non-Temporal Loads/Stores" of the
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`Cortex-A57 Software Optimization Guide`_.
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--------------
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*Copyright (c) 2014-2016, ARM Limited and Contributors. All rights reserved.*
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.. _Cortex-A53 MPCore Software Developers Errata Notice: http://infocenter.arm.com/help/topic/com.arm.doc.epm048406/index.html
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.. _Cortex-A57 MPCore Software Developers Errata Notice: http://infocenter.arm.com/help/topic/com.arm.doc.epm049219/cortex_a57_mpcore_software_developers_errata_notice.pdf
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.. _Firmware Design guide: firmware-design.rst
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.. _Cortex-A57 Software Optimization Guide: http://infocenter.arm.com/help/topic/com.arm.doc.uan0015b/Cortex_A57_Software_Optimization_Guide_external.pdf
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