[PATCH v2] 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 at centralesupelec.fr>
---
changes in v2 :
	- modified patch description
	- removed additional comments on testing
	- removed a check on architecture version of ETM
	- generated using "git format-patch"
	- same email address in from: and SOB
	
  drivers/hwtracing/coresight/coresight-etm.h         |  3 +++
  drivers/hwtracing/coresight/coresight-etm3x-sysfs.c | 12 ++++++++++++
  2 files changed, 15 insertions(+)

diff --git a/drivers/hwtracing/coresight/coresight-etm.h 
b/drivers/hwtracing/coresight/coresight-etm.h
index 4a18ee4..7a34860 100644
--- a/drivers/hwtracing/coresight/coresight-etm.h
+++ b/drivers/hwtracing/coresight/coresight-etm.h
@@ -110,8 +110,11 @@
  #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..4e0eab7 100644
--- a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
+++ b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
@@ -164,6 +164,18 @@ 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) {
+		if (config->mode & ETM_MODE_BBROAD)
+			dev_warn(drvdata->dev, "behavior is unpredictable\n");
+		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