UPSTREAM: dt-bindings: arm: coresight: Add support for coresight-loses-context-with-cpu

Some coresight components, because of choices made during hardware
integration, require their state to be saved and restored across CPU low
power states.

The software has no reliable method of detecting when save/restore is
required thus let's add a binding to inform the kernel.

Signed-off-by: Andrew Murray <andrew.murray@arm.com>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20191104181251.26732-3-mathieu.poirier@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(Upstream commit b7909065e8).

Bug: 140266694
Change-Id: Ie43bcbe7c80de3efef1f77900fe04595dc4904e0
Signed-off-by: Yabin Cui <yabinc@google.com>

Documentation/devicetree/bindings/arm/coresight.txt

@@ -75,6 +75,15 @@ its hardware characteristcs.
 
 	* port or ports: same as above.
 
+* Optional properties for all components:
+
+	* arm,coresight-loses-context-with-cpu : boolean. Indicates that the
+	  hardware will lose register context on CPU power down (e.g. CPUIdle).
+	  An example of where this may be needed are systems which contain a
+	  coresight component and CPU in the same power domain. When the CPU
+	  powers down the coresight component also powers down and loses its
+	  context. This property is currently only used for the ETM 4.x driver.
+
 * Optional properties for ETM/PTMs:
 
 	* arm,cp14: must be present if the system accesses ETM/PTM management