[PATCH v3 16/31] coresight: Add callback to determine if context save/restore is needed

[Mike Leach]

Hi Leo

On Mon, 15 Sept 2025 at 11:34, Leo Yan <leo.yan at arm.com> wrote:
>
> Add a callback in the source device that returns a boolean indicating
> whether context save and restore operations are required. The save and
> restore flow is skipped if the callback returns false.
>
> The ETMv4 driver implements its own version's callback.
>
> Signed-off-by: Leo Yan <leo.yan at arm.com>
> ---
>  drivers/hwtracing/coresight/coresight-core.c       | 16 +++++++++++-
>  drivers/hwtracing/coresight/coresight-etm4x-core.c | 30 +++++++++++++++++-----
>  include/linux/coresight.h                          |  2 ++
>  3 files changed, 40 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index f944a610c85e9e3fce43497543ccc48ab7c2c0d9..94803cacf1a374ae8a3b9513d7d029d5c77d5925 100644
> --- a/drivers/hwtracing/coresight/coresight-core.c
> +++ b/drivers/hwtracing/coresight/coresight-core.c
> @@ -423,6 +423,20 @@ int coresight_resume_source(struct coresight_device *csdev)
>  }
>  EXPORT_SYMBOL_GPL(coresight_resume_source);
>
> +static bool coresight_need_save_restore_source(struct coresight_device *csdev)
> +{
> +       if (!csdev)
> +               return false;
> +
> +       if (source_ops(csdev)->need_context_save_restore)

check the actual save and restore ops here too?

> +               return source_ops(csdev)->need_context_save_restore(csdev);
> +
> +       if (coresight_get_mode(csdev))
> +               return true;
> +

Not needed - should decide only on the previous
need_context_save_restore() test.
Components such as STM, ETR, ETB all use the mode status, but may not
support / need save and restore.

> +       return false;
> +}
> +
>  static int coresight_save_source(struct coresight_device *csdev)
>  {
>         if (csdev && source_ops(csdev)->save)
> @@ -1597,7 +1611,7 @@ static int coresight_cpu_pm_notify(struct notifier_block *nb, unsigned long cmd,
>         unsigned int cpu = smp_processor_id();
>         struct coresight_device *source = per_cpu(csdev_source, cpu);
>
> -       if (!source)
> +       if (!coresight_need_save_restore_source(source))
>                 return NOTIFY_OK;
>
>         switch (cmd) {
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index ec7e8d09ce58d62dac826fba9edafc967504a1a5..66aefdb002f075446572df9c4eed9093da19a066 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -1839,6 +1839,21 @@ static int etm4_dying_cpu(unsigned int cpu)
>         return 0;
>  }
>
> +static bool etm4_need_context_save_restore(struct coresight_device *csdev)
> +{
> +       if (pm_save_enable != PARAM_PM_SAVE_SELF_HOSTED)
> +               return false;
> +
> +       /*
> +        * Save and restore the ETM Trace registers only if
> +        * the ETM is active.
> +        */
> +       if (coresight_get_mode(csdev))
> +               return true;
> +
> +       return false;
> +}
> +
>  static int __etm4_cpu_save(struct etmv4_drvdata *drvdata)
>  {
>         int ret = 0;
> @@ -1927,13 +1942,14 @@ static void etm4_cpu_restore(struct coresight_device *csdev)
>  }
>
>  static const struct coresight_ops_source etm4_source_ops = {
> -       .cpu_id         = etm4_cpu_id,
> -       .enable         = etm4_enable,
> -       .disable        = etm4_disable,
> -       .resume_perf    = etm4_resume_perf,
> -       .pause_perf     = etm4_pause_perf,
> -       .save           = etm4_cpu_save,
> -       .restore        = etm4_cpu_restore,
> +       .cpu_id                    = etm4_cpu_id,
> +       .enable                    = etm4_enable,
> +       .disable                   = etm4_disable,
> +       .resume_perf               = etm4_resume_perf,
> +       .pause_perf                = etm4_pause_perf,
> +       .save                      = etm4_cpu_save,
> +       .restore                   = etm4_cpu_restore,

Above are just white space change noise as far as I can see.

> +       .need_context_save_restore = etm4_need_context_save_restore,
>  };
>
>  static const struct coresight_ops etm4_cs_ops = {
> diff --git a/include/linux/coresight.h b/include/linux/coresight.h
> index d0764a9c7692181d2619c277acb83701c6b0115e..39781ba24ee2ad9f3065770409aafb0e5af57fa8 100644
> --- a/include/linux/coresight.h
> +++ b/include/linux/coresight.h
> @@ -400,6 +400,7 @@ struct coresight_ops_link {
>   * @disable:   disables tracing for a source.
>   * @resume_perf: resumes tracing for a source in perf session.
>   * @pause_perf:        pauses tracing for a source in perf session.
> + * @need_context_save_restore: if need to save and restore context.
>   * @save:      save context for a source.
>   * @restore:   restore context for a source.
>   */
> @@ -411,6 +412,7 @@ struct coresight_ops_source {
>                         struct perf_event *event);
>         int (*resume_perf)(struct coresight_device *csdev);
>         void (*pause_perf)(struct coresight_device *csdev);
> +       bool (*need_context_save_restore)(struct coresight_device *csdev);
>         int (*save)(struct coresight_device *csdev);
>         void (*restore)(struct coresight_device *csdev);
>  };
>
> --
> 2.34.1
>

Regards

Mike

-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK