Add documentation for CPU specific abstraction and Errata workarounds
This patch adds documentation for CPU specific abstraction in the firmware-
design.md and adds a new document cpu-errata-workarounds.md to describe
the cpu errata workaround build flags.
Change-Id: Ia08c2fec0b868a0a107d0264e87a60182797a1bd
diff --git a/docs/cpu-errata-workarounds.md b/docs/cpu-errata-workarounds.md
new file mode 100644
index 0000000..73e8e18
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+++ b/docs/cpu-errata-workarounds.md
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+ARM CPU Errata Workarounds
+==========================
+
+ARM Trusted Firmware exports a series of build flags which controls the
+errata workarounds that are applied to each CPU by the reset handler. The
+errata details can be found in the CPU specifc errata documents published
+by ARM. The errata workarounds are implemented for a particular revision
+or a set of processor revisions. This check is done in the debug build.
+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 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 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.
+
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+_Copyright (c) 2014, ARM Limited and Contributors. All rights reserved._