coresight: etm4x: Save/restore state across CPU low power states

Some hardware will ignore bit TRCPDCR.PU which is used to signal
to hardware that power should not be removed from the trace unit.
Let's mitigate against this by conditionally saving and restoring
the trace unit state when the CPU enters low power states.

This patchset introduces a firmware property named
'arm,coresight-loses-context-with-cpu' - when this is present the
hardware state will be conditionally saved and restored.

A module parameter 'pm_save_enable' is also introduced which can
be configured to override the firmware property. This can be set
to never allow save/restore or to conditionally allow it (only for
self-hosted). The default value is determined by firmware.

We avoid saving the hardware state when self-hosted coresight isn't
in use to reduce PM latency - we can't determine this by reading the
claim tags (TRCCLAIMCLR) as these are 'trace' registers which need
power and clocking, something we can't easily provide in the PM
context. Therefore we rely on the existing drvdata->mode internal
state that is set when self-hosted coresight is used (and powered).

Signed-off-by: Andrew Murray <andrew.murray@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20191104181251.26732-2-mathieu.poirier@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/linux/coresight.h b/include/linux/coresight.h
index a2b68823717b..44e552de419c 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h
@@ -285,6 +285,8 @@ extern void coresight_disclaim_device(void __iomem *base);
 extern void coresight_disclaim_device_unlocked(void __iomem *base);
 extern char *coresight_alloc_device_name(struct coresight_dev_list *devs,
 					 struct device *dev);
+
+extern bool coresight_loses_context_with_cpu(struct device *dev);
 #else
 static inline struct coresight_device *
 coresight_register(struct coresight_desc *desc) { return NULL; }
@@ -307,6 +309,10 @@ static inline int coresight_claim_device(void __iomem *base)
 static inline void coresight_disclaim_device(void __iomem *base) {}
 static inline void coresight_disclaim_device_unlocked(void __iomem *base) {}
 
+static inline bool coresight_loses_context_with_cpu(struct device *dev)
+{
+	return false;
+}
 #endif
 
 extern int coresight_get_cpu(struct device *dev);