[PATCH v3] coresight-etm4x: add isb() before reading the TRCSTATR

[yuanfang zhang]

From: Yuanfang Zhang <quic_yuanfang@xxxxxxxxxxx>

As recommended by section 4.3.7 ("Synchronization when using system
instructions to progrom the trace unit") of ARM IHI 0064H.b, the
self-hosted trace analyzer must perform a Context synchronization
event between writing to the TRCPRGCTLR and reading the TRCSTATR.

Fixes: ebddaad09e10 ("coresight: etm4x: Add missing single-shot control API to sysfs")
Signed-off-by: Yuanfang Zhang <quic_yuanfang@xxxxxxxxxxx>
---
Changes in V3:
1. Remove dsb(sy) after polling TRCSTATR.
2. Add isb() after polling TRCSTATR.
---
 .../hwtracing/coresight/coresight-etm4x-core.c   | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 66d44a404ad0..c6ea00bba0cc 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -531,7 +531,6 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
 	 * As recommended by section 4.3.7 ("Synchronization when using the
 	 * memory-mapped interface") of ARM IHI 0064D
 	 */
-	dsb(sy);
 	isb();
 
 done:
@@ -906,10 +905,25 @@ static void etm4_disable_hw(void *info)
 	tsb_csync();
 	etm4x_relaxed_write32(csa, control, TRCPRGCTLR);
 
+	/*
+	 * As recommended by section 4.3.7 ("Synchronization when using system
+	 * instructions to progrom the trace unit") of ARM IHI 0064H.b, the
+	 * self-hosted trace analyzer must perform a Context synchronization
+	 * event between writing to the TRCPRGCTLR and reading the TRCSTATR.
+	 */
+	if (!csa->io_mem)
+		isb();
+
 	/* wait for TRCSTATR.PMSTABLE to go to '1' */
 	if (coresight_timeout(csa, TRCSTATR, TRCSTATR_PMSTABLE_BIT, 1))
 		dev_err(etm_dev,
 			"timeout while waiting for PM stable Trace Status\n");
+	/*
+	 * As recommended by section 4.3.7 (Synchronization of register updates)
+	 * of ARM IHI 0064H.b.
+	 */
+	isb();
+
 	/* read the status of the single shot comparators */
 	for (i = 0; i < drvdata->nr_ss_cmp; i++) {
 		config->ss_status[i] =
-- 
2.34.1