[v2,0/5] coresight: etm4x: save/restore ETMv4 context across CPU low power states

Message

Andrew Murray June 27, 2019, 8:35 a.m. UTC

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-needs-save-restore' - 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.

The hardware state is only ever saved and restored when the claim
tags indicate that self-hosted mode is in use.

Changes since v1:

 - Rebased onto coresight/next

 - Correcly pass bit number rather than BIT macro to coresight_timeout

 - Abort saving state if a timeout occurs

 - Fix completely broken pm_notify handling and unregister handler on error

 - Use state_needs_restore to ensure state is restored only once

 - Add module parameter description to existing boot_enable parameter
   and use module_param instead of module_param_named

 - Add firmware bindings for coresight-needs-save-restore

 - Rename 'disable_pm_save' to 'pm_save_enable' which allows for
   disabled, enabled or firmware

 - Update comment on etm4_os_lock, it incorrectly indicated that
   the code unlocks the trace registers

 - Add comments to explain use of OS lock during save/restore

 - Fix incorrect error description whilst waiting for PM stable

 - Add WARN_ON_ONCE when cpu isn't as expected during save/restore

 - Various updates to commit messages


Andrew Murray (5):
  coresight: etm4x: remove superfluous setting of os_unlock
  coresight: etm4x: use explicit barriers on enable/disable
  coresight: etm4x: use module_param instead of module_param_named
  coresight: etm4x: improve clarity of etm4_os_unlock comment
  coresight: etm4x: save/restore state across CPU low power states

 .../devicetree/bindings/arm/coresight.txt     |   3 +
 drivers/hwtracing/coresight/coresight-etm4x.c | 315 +++++++++++++++++-
 drivers/hwtracing/coresight/coresight-etm4x.h |  66 ++++
 drivers/hwtracing/coresight/coresight.c       |   2 +-
 include/linux/coresight.h                     |   8 +
 5 files changed, 387 insertions(+), 7 deletions(-)