[PATCH v4 07/11] coresight: etm4x: Properly control filter in CPU idle with FEAT_TRF

[Suzuki K Poulose]

On 24/10/2025 17:45, Leo Yan wrote:
> If a CPU supports FEAT_TRF, as described in the section K5.5 "Context
> switching", Arm ARM (ARM DDI 0487 L.a), it defines a flow to prohibit
> program-flow trace, execute a TSB CSYNC instruction for flushing,
> followed by clearing TRCPRGCTLR.EN bit.
> 
> To restore the state, the reverse sequence is required.
> 
> This differs from the procedure described in the section 3.4.1 "The
> procedure when powering down the PE" of ARM IHI0064H.b, which involves
> the OS Lock to prevent external debugger accesses and implicitly
> disables trace.
> 
> To be compatible with different ETM versions, explicitly control trace
> unit using etm4_disable_trace_unit() and etm4_enable_trace_unit()
> during CPU idle to comply with FEAT_TRF.
> 
> As a result, the save states for TRFCR_ELx and trcprgctlr are redundant,
> remove them.
> 
> Fixes: f188b5e76aae ("coresight: etm4x: Save/restore state across CPU low power states")
> Reviewed-by: Mike Leach <mike.leach 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-etm4x-core.c | 28 ++++++++++++++++------
>   drivers/hwtracing/coresight/coresight-etm4x.h      |  3 ---
>   2 files changed, 21 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index 7eb30e85bf03d1eda8212faa3c831338b70f86c3..df3260f2dfa72456c60fba4a8fa655fb6b48b95b 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -1882,9 +1882,18 @@ static int __etm4_cpu_save(struct etmv4_drvdata *drvdata)
>   		goto out;
>   	}
>  



> +	if (!drvdata->paused)
> +		etm4_disable_trace_unit(drvdata);
> +
> +	/*
> +	 * As recommended by section 4.3.7 (Synchronization of register updates)
> +	 * of ARM IHI 0064H.b, the self-hosted trace analyzer always executes an
> +	 * ISB instruction after programming the trace unit registers.
> +	 */
> +	isb();
> +



>   	/* Unlock the OS lock to re-enable trace and external debug access */
>   	etm4_os_unlock(drvdata);
> +
> +	if (!drvdata->paused)
> +		etm4_enable_trace_unit(drvdata);
> +
> +	/*
> +	 * As recommended by section 4.3.7 (Synchronization of register updates)
> +	 * of ARM IHI 0064H.b, the self-hosted trace analyzer always executes an
> +	 * ISB instruction after programming the trace unit registers.
> +	 */
> +	isb();

I guess these ISBs are not required according to the comment on the 
previous patch ? Otherwise looks good to me.

Suzuki


> +
>   	etm4_cs_lock(drvdata, csa);
>   }
>   
>   static void etm4_cpu_restore(struct etmv4_drvdata *drvdata)
>   {
> -	if (drvdata->trfcr)
> -		write_trfcr(drvdata->save_trfcr);
>   	if (drvdata->state_needs_restore)
>   		__etm4_cpu_restore(drvdata);
>   }
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
> index 13ec9ecef46f5b60a38c464e8ebde3ef72e7d50b..b8796b4271025f6aba79fe3cd6e4d17d0b56952d 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> @@ -866,7 +866,6 @@ struct etmv4_config {
>    * struct etm4_save_state - state to be preserved when ETM is without power
>    */
>   struct etmv4_save_state {
> -	u32	trcprgctlr;
>   	u32	trcprocselr;
>   	u32	trcconfigr;
>   	u32	trcauxctlr;
> @@ -980,7 +979,6 @@ struct etmv4_save_state {
>    *		at runtime, due to the additional setting of TRFCR_CX when
>    *		in EL2. Otherwise, 0.
>    * @config:	structure holding configuration parameters.
> - * @save_trfcr:	Saved TRFCR_EL1 register during a CPU PM event.
>    * @save_state:	State to be preserved across power loss
>    * @state_needs_restore: True when there is context to restore after PM exit
>    * @skip_power_up: Indicates if an implementation can skip powering up
> @@ -1037,7 +1035,6 @@ struct etmv4_drvdata {
>   	bool				lpoverride;
>   	u64				trfcr;
>   	struct etmv4_config		config;
> -	u64				save_trfcr;
>   	struct etmv4_save_state		*save_state;
>   	bool				state_needs_restore;
>   	bool				skip_power_up;
>