[PATCH v3] Adding missing features of Coresight PTM components

[Muhammad Abdul WAHAB]

In the current driver for Coresight components, two features of PTM
components are missing:

1. Branch Broadcasting (present also in ETM but called Branch Output)
2. Return Stack (only present in PTM v1.0 and PTMv1.1)

These features can be added simply to the code using `mode` field of
`etm_config` struct.

1. **Branch Broadcast** : The branch broadcast feature is present in ETM
components as well and is called Branch output. It allows to retrieve
addresses for direct branch addresses alongside the indirect branch
addresses. For example, it could be useful in cases when tracing without
source code.
2. **Return Stack** : The return stack option allows to retrieve the return
 addresses of function calls. It can be useful to avoid CRA
(Code Reuse Attacks) by keeping a shadowstack.

Signed-off-by: Muhammad Abdul Wahab <muhammadabdul.wahab@xxxxxxxxxxxxxxxxxx>
---
changes in v3 :
	- deleted warning message
	- bit field definition of Branch Broadcast and Return Stack

 drivers/hwtracing/coresight/coresight-etm.h         |  5 +++++
 drivers/hwtracing/coresight/coresight-etm3x-sysfs.c | 10 ++++++++++
 2 files changed, 15 insertions(+)

diff --git a/drivers/hwtracing/coresight/coresight-etm.h 
b/drivers/hwtracing/coresight/coresight-etm.h
index 4a18ee4..ad063d7 100644
--- a/drivers/hwtracing/coresight/coresight-etm.h
+++ b/drivers/hwtracing/coresight/coresight-etm.h
@@ -89,11 +89,13 @@
 /* ETMCR - 0x00 */
 #define ETMCR_PWD_DWN		BIT(0)
 #define ETMCR_STALL_MODE	BIT(7)
+#define ETMCR_BRANCH_BROADCAST	BIT(8)
 #define ETMCR_ETM_PRG		BIT(10)
 #define ETMCR_ETM_EN		BIT(11)
 #define ETMCR_CYC_ACC		BIT(12)
 #define ETMCR_CTXID_SIZE	(BIT(14)|BIT(15))
 #define ETMCR_TIMESTAMP_EN	BIT(28)
+#define ETMCR_RETURN_STACK	BIT(29)
 /* ETMCCR - 0x04 */
 #define ETMCCR_FIFOFULL		BIT(23)
 /* ETMPDCR - 0x310 */
@@ -110,8 +112,11 @@
 #define ETM_MODE_STALL		BIT(2)
 #define ETM_MODE_TIMESTAMP	BIT(3)
 #define ETM_MODE_CTXID		BIT(4)
+#define ETM_MODE_BBROAD		BIT(5)
+#define ETM_MODE_RET_STACK	BIT(6)
 #define ETM_MODE_ALL		(ETM_MODE_EXCLUDE | ETM_MODE_CYCACC | \
 				 ETM_MODE_STALL | ETM_MODE_TIMESTAMP | \
+				 ETM_MODE_BBROAD | ETM_MODE_RET_STACK | \
 				 ETM_MODE_CTXID | ETM_MODE_EXCL_KERN | \
 				 ETM_MODE_EXCL_USER)

diff --git a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c 
b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
index 5ea0909..a76009a 100644
--- a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
+++ b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
@@ -164,6 +164,16 @@ static ssize_t mode_store(struct device *dev,
 	else
 		config->ctrl &= ~ETMCR_CTXID_SIZE;

+	if (config->mode & ETM_MODE_BBROAD)
+		config->ctrl |= ETMCR_BRANCH_BROADCAST;
+	else
+		config->ctrl &= ~ETMCR_BRANCH_BROADCAST;
+
+	if (config->mode & ETM_MODE_RET_STACK)
+		config->ctrl |= ETMCR_RETURN_STACK_EN;
+	else
+		config->ctrl &= ~ETMCR_RETURN_STACK_EN;
+
 	if (config->mode & (ETM_MODE_EXCL_KERN | ETM_MODE_EXCL_USER))
 		etm_config_trace_mode(config);

--
1.9.1