Re: [PATCH v2 01/10] coresight: etm4x: Save restore TRFCR_EL1

[Anshuman Khandual]

On 7/23/21 6:16 PM, Suzuki K Poulose wrote:
> When the CPU enters a low power mode, the TRFCR_EL1 contents could be
> reset. Thus we need to save/restore the TRFCR_EL1 along with the ETM4x
> registers to allow the tracing.
> 
> The TRFCR related helpers are in a new header file, as we need to use
> them for TRBE in the later patches.
> 
> Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Cc: Mike Leach <mike.leach@xxxxxxxxxx>
> Cc: Leo Yan <leo.yan@xxxxxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> ---
> Changes since v1:
>  - Moved the TRFCR helpers in to a new header file
> ---
>  .../coresight/coresight-etm4x-core.c          | 43 +++++++++++++------
>  drivers/hwtracing/coresight/coresight-etm4x.h |  2 +
>  .../coresight/coresight-self-hosted-trace.h   | 25 +++++++++++
>  3 files changed, 58 insertions(+), 12 deletions(-)
>  create mode 100644 drivers/hwtracing/coresight/coresight-self-hosted-trace.h
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index da27cd4a3c38..3e548dac9b05 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -39,6 +39,7 @@
>  
>  #include "coresight-etm4x.h"
>  #include "coresight-etm-perf.h"
> +#include "coresight-self-hosted-trace.h"
>  
>  static int boot_enable;
>  module_param(boot_enable, int, 0444);
> @@ -985,7 +986,7 @@ static void cpu_enable_tracing(struct etmv4_drvdata *drvdata)
>  	if (is_kernel_in_hyp_mode())
>  		trfcr |= TRFCR_EL2_CX;
>  
> -	write_sysreg_s(trfcr, SYS_TRFCR_EL1);
> +	write_trfcr(trfcr);
>  }
>  
>  static void etm4_init_arch_data(void *info)
> @@ -1528,7 +1529,7 @@ static void etm4_init_trace_id(struct etmv4_drvdata *drvdata)
>  	drvdata->trcid = coresight_get_trace_id(drvdata->cpu);
>  }
>  
> -static int etm4_cpu_save(struct etmv4_drvdata *drvdata)
> +static int __etm4_cpu_save(struct etmv4_drvdata *drvdata)
>  {
>  	int i, ret = 0;
>  	struct etmv4_save_state *state;
> @@ -1667,7 +1668,23 @@ static int etm4_cpu_save(struct etmv4_drvdata *drvdata)
>  	return ret;
>  }
>  
> -static void etm4_cpu_restore(struct etmv4_drvdata *drvdata)
> +static int etm4_cpu_save(struct etmv4_drvdata *drvdata)
> +{
> +	int ret = 0;
> +
> +	/* Save the TRFCR irrespective of whether the ETM is ON */
> +	if (drvdata->trfc)
> +		drvdata->save_trfcr = read_trfcr();
> +	/*
> +	 * Save and restore the ETM Trace registers only if
> +	 * the ETM is active.
> +	 */
> +	if (local_read(&drvdata->mode) && drvdata->save_state)
> +		ret = __etm4_cpu_save(drvdata);
> +	return ret;
> +}
> +
> +static void __etm4_cpu_restore(struct etmv4_drvdata *drvdata)
>  {
>  	int i;
>  	struct etmv4_save_state *state = drvdata->save_state;
> @@ -1763,6 +1780,14 @@ static void etm4_cpu_restore(struct etmv4_drvdata *drvdata)
>  	etm4_cs_lock(drvdata, csa);
>  }
>  
> +static void etm4_cpu_restore(struct etmv4_drvdata *drvdata)
> +{
> +	if (drvdata->trfc)
> +		write_trfcr(drvdata->save_trfcr);
> +	if (drvdata->state_needs_restore)
> +		__etm4_cpu_restore(drvdata);
> +}
> +
>  static int etm4_cpu_pm_notify(struct notifier_block *nb, unsigned long cmd,
>  			      void *v)
>  {
> @@ -1774,23 +1799,17 @@ static int etm4_cpu_pm_notify(struct notifier_block *nb, unsigned long cmd,
>  
>  	drvdata = etmdrvdata[cpu];
>  
> -	if (!drvdata->save_state)
> -		return NOTIFY_OK;
> -
>  	if (WARN_ON_ONCE(drvdata->cpu != cpu))
>  		return NOTIFY_BAD;
>  
>  	switch (cmd) {
>  	case CPU_PM_ENTER:
> -		/* save the state if self-hosted coresight is in use */
> -		if (local_read(&drvdata->mode))
> -			if (etm4_cpu_save(drvdata))
> -				return NOTIFY_BAD;
> +		if (etm4_cpu_save(drvdata))
> +			return NOTIFY_BAD;
>  		break;
>  	case CPU_PM_EXIT:
>  	case CPU_PM_ENTER_FAILED:
> -		if (drvdata->state_needs_restore)
> -			etm4_cpu_restore(drvdata);
> +		etm4_cpu_restore(drvdata);
>  		break;
>  	default:
>  		return NOTIFY_DONE;
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
> index e5b79bdb9851..82cba16b73a6 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> @@ -921,6 +921,7 @@ struct etmv4_save_state {
>   * @lpoverride:	If the implementation can support low-power state over.
>   * @trfc:	If the implementation supports Arm v8.4 trace filter controls.
>   * @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
> @@ -973,6 +974,7 @@ struct etmv4_drvdata {
>  	bool				lpoverride;
>  	bool				trfc;
>  	struct etmv4_config		config;
> +	u64				save_trfcr;
>  	struct etmv4_save_state		*save_state;
>  	bool				state_needs_restore;
>  	bool				skip_power_up;
> diff --git a/drivers/hwtracing/coresight/coresight-self-hosted-trace.h b/drivers/hwtracing/coresight/coresight-self-hosted-trace.h
> new file mode 100644
> index 000000000000..53b35a28075e
> --- /dev/null
> +++ b/drivers/hwtracing/coresight/coresight-self-hosted-trace.h
> @@ -0,0 +1,25 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +/*
> + * Arm v8 Self-Hosted trace support.
> + *
> + * Copyright (C) 2021 ARM Ltd.
> + */
> +
> +#ifndef __CORESIGHT_SELF_HOSTED_TRACE_H
> +#define __CORESIGHT_SELF_HOSTED_TRACE_H
> +
> +#include <asm/sysreg.h>
> +
> +static inline u64 read_trfcr(void)
> +{
> +	return read_sysreg_s(SYS_TRFCR_EL1);
> +}
> +
> +static inline void write_trfcr(u64 val)
> +{
> +	write_sysreg_s(val, SYS_TRFCR_EL1);
> +	isb();
> +}
> +
> +#endif			/*  __CORESIGHT_SELF_HOSTED_TRACE_H */
> 

Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>