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switch-l4t-atf/docs/cpu-specific-build-macros.md
Andre Przywara b75dc0e41c Add workaround for ARM Cortex-A53 erratum 855873 
ARM erratum 855873 applies to all Cortex-A53 CPUs.
The recommended workaround is to promote "data cache clean"
instructions to "data cache clean and invalidate" instructions.
For core revisions of r0p3 and later this can be done by setting a bit
in the CPUACTLR_EL1 register, so that hardware takes care of the promotion.
As CPUACTLR_EL1 is both IMPLEMENTATION DEFINED and can be trapped to EL3,
we set the bit in firmware.
Also we dump this register upon crashing to provide more debug
information.

Enable the workaround for the Juno boards.

Change-Id: I3840114291958a406574ab6c49b01a9d9847fec8
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
2017-03-20 10:57:46 +00:00

6.4 KiB
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ARM CPU Specific Build Macros

Contents

  1. Introduction

  2. CPU Errata Workarounds

  3. CPU Specific optimizations

  4. Introduction

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.

  1. CPU Errata Workarounds

ARM Trusted Firmware 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:

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 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 are 0 by default, that is, disabled. Any other value will enable it.

For Cortex-A53, following errata build flags are defined :

  • 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_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_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-A57, 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_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.

  1. 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.

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