[PATCH v3 22/26] coresight: etm4x: Add necessary synchronization for sysreg access

Suzuki K Poulose
2020-10-28T22:11:18Z

As per the specification any update to the TRCPRGCTLR must be synchronized
by a context synchronization event (in our case an explicist ISB) before
the TRCSTATR is checked.

Cc: Mike Leach <mike.leach@linaro.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index e36bc1c722c7..4bc2f15b6332 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -178,6 +178,15 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
/* Disable the trace unit before programming trace registers */
etm4x_relaxed_write32(csa, 0, TRCPRGCTLR);

+ /*
+ * If we use system instructions, we need to synchronize the
+ * write to the TRCPRGCTLR, before accessing the TRCSTATR.
+ * See ARM IHI0064F, section
+ * "4.3.7 Synchronization of register updates"
+ */
+ if (!csa->io_mem)
+ isb();
+
/* wait for TRCSTATR.IDLE to go up */
if (coresight_timeout(csa, TRCSTATR, TRCSTATR_IDLE_BIT, 1))
dev_err(etm_dev,
@@ -256,6 +265,10 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
/* Enable the trace unit */
etm4x_relaxed_write32(csa, 1, TRCPRGCTLR);

+ /* Synchronize the register updates for sysreg access */
+ if (!csa->io_mem)
+ isb();
+
/* wait for TRCSTATR.IDLE to go back down to '0' */
if (coresight_timeout(csa, TRCSTATR, TRCSTATR_IDLE_BIT, 0))
dev_err(etm_dev,
--
2.24.1