ARM CPU Specific Build Macros

Contents

1. Introduction
2. CPU Errata Workarounds
3. CPU Specific optimizations

1. 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.

2. 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 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 is ERRATA_<Processor name>_<ID> where the Processor name is either A57 for the Cortex_A57 CPU or A53 for Cortex_A53 CPU.

All workarounds are disabled by default. The platform is reponsible 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.

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_813420: This applies errata 813420 workaround to Cortex-A57 CPU. This needs to be enabled only for revision r0p0 of the CPU.

• 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.

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