coresight: etm4x: Properly control filter in CPU idle with FEAT_TRF

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@linaro.org>
Tested-by: James Clark <james.clark@linaro.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20251111-arm_coresight_power_management_fix-v6-6-f55553b6c8b3@arm.com

2 files changed, 7 insertions, 10 deletions

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 5e707d082537..fdda924a2c71 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -1858,9 +1858,11 @@ static int __etm4_cpu_save(struct etmv4_drvdata *drvdata)
 		goto out;
 	}
 
+	if (!drvdata->paused)
+		etm4_disable_trace_unit(drvdata);
+
 	state = drvdata->save_state;
 
-	state->trcprgctlr = etm4x_read32(csa, TRCPRGCTLR);
 	if (drvdata->nr_pe)
 		state->trcprocselr = etm4x_read32(csa, TRCPROCSELR);
 	state->trcconfigr = etm4x_read32(csa, TRCCONFIGR);
@@ -1970,9 +1972,6 @@ static int etm4_cpu_save(struct etmv4_drvdata *drvdata)
 {
 	int ret = 0;
 
-	/* Save the TRFCR irrespective of whether the ETM is ON */
-	if (drvdata->trfcr)
-		drvdata->save_trfcr = read_trfcr();
 	/*
 	 * Save and restore the ETM Trace registers only if
 	 * the ETM is active.
@@ -1994,7 +1993,6 @@ static void __etm4_cpu_restore(struct etmv4_drvdata *drvdata)
 	etm4_cs_unlock(drvdata, csa);
 	etm4x_relaxed_write32(csa, state->trcclaimset, TRCCLAIMSET);
 
-	etm4x_relaxed_write32(csa, state->trcprgctlr, TRCPRGCTLR);
 	if (drvdata->nr_pe)
 		etm4x_relaxed_write32(csa, state->trcprocselr, TRCPROCSELR);
 	etm4x_relaxed_write32(csa, state->trcconfigr, TRCCONFIGR);
@@ -2079,13 +2077,15 @@ static void __etm4_cpu_restore(struct etmv4_drvdata *drvdata)
 
 	/* Unlock the OS lock to re-enable trace and external debug access */
 	etm4_os_unlock(drvdata);
+
+	if (!drvdata->paused)
+		etm4_enable_trace_unit(drvdata);
+
 	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 13ec9ecef46f..b8796b427102 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;