Re: [PATCH v4 0/6] coresight: etm4x: save/restore ETMv4 context across CPU low power states

[Andrew Murray <andrew.murray@arm.com>]

On Tue, Jul 30, 2019 at 02:12:20PM -0600, Mathieu Poirier wrote:
> Hi Andrew,
> 
> On Tue, Jul 30, 2019 at 01:51:51PM +0100, Andrew Murray wrote:
> > 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 a self-hosted
> > coresight is in use.
> > 
> > Changes since v3:
> > 
> >  - Only save/restore when self-hosted is being used and detect this
> >    without relying on the coresight registers (which may not be
> >    available)
> > 
> >  - Only allocate memory for etmv4_save_state at probe time when
> >    configuration indicates it may be used
> > 
> >  - Set pm_save_enable param to 0444 such that it is static after
> >    boot
> > 
> >  - Save/restore TRCPDCR
> > 
> >  - Add missing comments to struct etm4_drvdata documentation
> > 
> >  - Rebased onto coresight/next (8f1f9857)
> > 
> > Changes since v2:
> > 
> >  - Move the PM notifier block from drvdata to file static
> > 
> >  - Add section names to document references
> > 
> >  - Add additional information to commit messages
> > 
> >  - Remove trcdvcvr and trcdvcmr from saved state and add a comment to
> >    describe why
> > 
> >  - Ensure TRCPDCR_PU is set after restore and add a comment to explain
> >    why we bother toggling TRCPDCR_PU on save/restore
> > 
> >  - Reword the pm_save_enable options and add comments
> > 
> >  - Miscellaneous style changes
> > 
> >  - Move device tree binding documentation to its own patch
> > 
> > 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 (6):
> >   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
> 
> I have picked up the first 4 patches, so no need to send them with your next
> revision.  Note that for patch 2/6 I have removed the "stable" tag as the patch
> doesn't apply to any of the stable tree.  Since I have another one like that in
> my tree I will rework both patches and send them directly to Greg for stable
> consideration.

Ah many thanks for this.

Andrew Murray

> 
> Thanks,
> Mathieu
> 
> 
> >   coresight: etm4x: save/restore state across CPU low power states
> >   dt-bindings: arm: coresight: Add support for
> >     coresight-needs-save-restore
> > 
> >  .../devicetree/bindings/arm/coresight.txt     |   3 +
> >  drivers/hwtracing/coresight/coresight-etm4x.c | 346 +++++++++++++++++-
> >  drivers/hwtracing/coresight/coresight-etm4x.h |  64 ++++
> >  3 files changed, 406 insertions(+), 7 deletions(-)
> > 
> > -- 
> > 2.21.0
> > 

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