[PATCH v6 05/19] coresight: Add callback to determine if PM is needed

[Suzuki K Poulose]

On 05/03/2026 10:17, Leo Yan wrote:
> Add a callback in the source device that returns a boolean indicating
> whether power management operations are required. The save and restore
> flow is skipped if the callback returns false.
> 
> The ETMv4 driver implements its own version's callback.
> 
> Reviewed-by: James Clark <james.clark at linaro.org>
> Tested-by: James Clark <james.clark at linaro.org>
> Signed-off-by: Leo Yan <leo.yan at arm.com>
> ---
>   drivers/hwtracing/coresight/coresight-core.c       |  9 ++++++++-
>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 16 ++++++++++++++++
>   include/linux/coresight.h                          |  1 +
>   3 files changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index 5f7930ef537e2877649c404858d9fe6f593af037..6956429ca507d850c8b8c62c65de4b6fe1a1740c 100644
> --- a/drivers/hwtracing/coresight/coresight-core.c
> +++ b/drivers/hwtracing/coresight/coresight-core.c
> @@ -1681,7 +1681,14 @@ static bool coresight_pm_is_needed(struct coresight_device *csdev)
>   	    !coresight_ops(csdev)->pm_restore_enable)
>   		return false;
>   
> -	return true;
> +	/*
> +	 * PM callbacks are provided but pm_is_neended() is absent, it means
> +	 * no extra check is needed.
> +	 */
> +	if (!coresight_ops(csdev)->pm_is_needed)
> +		return true;

Do we really need this call back ? The ETM can skip registering the PM 
ops when it is not needed (make them NULL) ? And the oresight_get_mode() 
is any way available for all devices and use that simply in the core 
function ?

Suzuki


> +
> +	return coresight_ops(csdev)->pm_is_needed(csdev);
>   }
>   
>   static int coresight_pm_save(struct coresight_device *csdev)
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index ab2031647616111d0689442149bcfdb0accbb218..d005983ee1e595f4ddc0b1f87596b1fbe4a0e41a 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -1861,6 +1861,21 @@ static int etm4_dying_cpu(unsigned int cpu)
>   	return 0;
>   }
>   
> +static bool etm4_need_save_restore_context(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 i, ret = 0;
> @@ -2136,6 +2151,7 @@ static const struct coresight_ops etm4_cs_ops = {
>   	.trace_id		= coresight_etm_get_trace_id,
>   	.pm_save_disable	= etm4_cpu_save,
>   	.pm_restore_enable	= etm4_cpu_restore,
> +	.pm_is_needed		= etm4_need_save_restore_context,
>   	.source_ops		= &etm4_source_ops,
>   };
>   
> diff --git a/include/linux/coresight.h b/include/linux/coresight.h
> index 63d77a064d9431d512b6407946c403f5c331d086..2de2ef94d2e046effb264cc97e5cd1a61e609249 100644
> --- a/include/linux/coresight.h
> +++ b/include/linux/coresight.h
> @@ -439,6 +439,7 @@ struct coresight_ops {
>   			struct coresight_device *sink);
>   	int (*pm_save_disable)(struct coresight_device *csdev);
>   	void (*pm_restore_enable)(struct coresight_device *csdev);
> +	bool (*pm_is_needed)(struct coresight_device *csdev);
>   	const struct coresight_ops_sink *sink_ops;
>   	const struct coresight_ops_link *link_ops;
>   	const struct coresight_ops_source *source_ops;
>