DSU erratum 936184 workaround

If the system is in near idle conditions, this erratum could cause a
deadlock or data corruption. This patch applies the workaround that
prevents this.

This DSU erratum affects only the DSUs that contain the ACP interface
and it was fixed in r2p0. The workaround is applied only to the DSUs
that are actually affected.

Link to respective Arm documentation:
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.epm138168/index.html

Change-Id: I033213b3077685130fc1e3f4f79c4d15d7483ec9
Signed-off-by: John Tsichritzis <john.tsichritzis@arm.com>

1 files changed, 28 insertions, 5 deletions

diff --git a/docs/cpu-specific-build-macros.rst b/docs/cpu-specific-build-macros.rst
index c11f64039..151c99e98 100644
--- a/docs/cpu-specific-build-macros.rst
+++ b/docs/cpu-specific-build-macros.rst
@@ -68,10 +68,10 @@ 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.
+The value of the build flags is 0 by default, that is, disabled. A value of 1
+will enable it.
 
-For Cortex-A53, following errata build flags are defined :
+For Cortex-A53, the 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.
@@ -97,7 +97,7 @@ For Cortex-A53, following errata build flags are defined :
    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 :
+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.
@@ -127,11 +127,33 @@ For Cortex-A57, following errata build flags are defined :
    CPU. This needs to be enabled only for revision <= r1p3 of the CPU.
 
 
-For Cortex-A72, following errata build flags are defined :
+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.
 
+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_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
 --------------------------
 
@@ -171,3 +193,4 @@ architecture that can be enabled by the platform as desired.
 .. _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
\ No newline at end of file