Re: [PATCH v2 1/6] coresight: Add config flag to enable branch broadcast

When enabled, all taken branch addresses are output, even if the branch
was because of a direct branch instruction. This enables reconstruction
of the program flow without having access to the memory image of the
code being executed.

Use bit 8 for the config option which would be the correct bit for
programming ETMv3. Although branch broadcast can't be enabled on ETMv3
because it's not in the define ETM3X_SUPPORTED_OPTIONS, using the
correct bit might help prevent future collisions or allow it to be
enabled if needed.

Signed-off-by: James Clark <redacted>
---
 drivers/hwtracing/coresight/coresight-etm-perf.c   |  2 ++
 drivers/hwtracing/coresight/coresight-etm4x-core.c | 10 ++++++++++
 include/linux/coresight-pmu.h                      |  2 ++
 3 files changed, 14 insertions(+)

diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
index c039b6ae206f..43bbd5dc3d3b 100644
--- a/drivers/hwtracing/coresight/coresight-etm-perf.c
+++ b/drivers/hwtracing/coresight/coresight-etm-perf.c

@@ -52,6 +52,7 @@ static DEFINE_PER_CPU(struct coresight_device *, csdev_src);
  * The PMU formats were orignally for ETMv3.5/PTM's ETMCR 'config';
  * now take them as general formats and apply on all ETMs.
  */
+PMU_FORMAT_ATTR(branch_broadcast, "config:"__stringify(ETM_OPT_BRANCH_BROADCAST));
 PMU_FORMAT_ATTR(cycacc,                "config:" __stringify(ETM_OPT_CYCACC));
 /* contextid1 enables tracing CONTEXTIDR_EL1 for ETMv4 */
 PMU_FORMAT_ATTR(contextid1,    "config:" __stringify(ETM_OPT_CTXTID));

@@ -97,6 +98,7 @@ static struct attribute *etm_config_formats_attr[] = {
        &format_attr_sinkid.attr,
        &format_attr_preset.attr,
        &format_attr_configid.attr,
+       &format_attr_branch_broadcast.attr,
        NULL,
 };

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index bf18128cf5de..04669ecc0efa 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c

@@ -692,6 +692,16 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
                ret = cscfg_csdev_enable_active_config(csdev, cfg_hash, preset);
        }

+       /* branch broadcast - enable if selected and supported */
+       if (attr->config & BIT(ETM_OPT_BRANCH_BROADCAST)) {
+               if (!drvdata->trcbb) {
+                       ret = -EINVAL;
+                       goto out;
+               } else {
+                       config->cfg |= BIT(ETM4_CFG_BIT_BB);
+               }
+       }
+
 out:
        return ret;
 }

diff --git a/include/linux/coresight-pmu.h b/include/linux/coresight-pmu.h
index 4ac5c081af93..6c2fd6cc5a98 100644
--- a/include/linux/coresight-pmu.h
+++ b/include/linux/coresight-pmu.h

@@ -18,6 +18,7 @@
  * ETMv3.5/PTM doesn't define ETMCR config bits with prefix "ETM3_" and
  * directly use below macros as config bits.
  */
+#define ETM_OPT_BRANCH_BROADCAST 8
 #define ETM_OPT_CYCACC         12
 #define ETM_OPT_CTXTID         14
 #define ETM_OPT_CTXTID2                15

@@ -25,6 +26,7 @@
 #define ETM_OPT_RETSTK         29

 /* ETMv4 CONFIGR programming bits for the ETM OPTs */
+#define ETM4_CFG_BIT_BB         3
 #define ETM4_CFG_BIT_CYCACC    4
 #define ETM4_CFG_BIT_CTXTID    6
 #define ETM4_CFG_BIT_VMID      7
--

2.28.0