Re: [PATCH V3 2/3] coresight: etm: Make cycle count threshold user configurable

On 8/11/23 14:22, Mike Leach wrote:

On Fri, 11 Aug 2023 at 04:46, Anshuman Khandual
[off-list ref] wrote:

quoted

Cycle counting is enabled, when requested and supported but with a default
threshold value ETM_CYC_THRESHOLD_DEFAULT i.e 0x100 getting into TRCCCCTLR,
representing the minimum interval between cycle count trace packets.

This makes cycle threshold user configurable, from the user space via perf
event attributes. Although it falls back using ETM_CYC_THRESHOLD_DEFAULT,
in case no explicit request. As expected it creates a sysfs file as well.

/sys/bus/event_source/devices/cs_etm/format/cc_threshold

New 'cc_threshold' uses 'event->attr.config3' as no more space is available
in 'event->attr.config1' or 'event->attr.config2'.

Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Mike Leach <redacted>
Cc: James Clark <redacted>
Cc: Leo Yan <redacted>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <redacted>
---
 drivers/hwtracing/coresight/coresight-etm-perf.c   |  2 ++
 drivers/hwtracing/coresight/coresight-etm4x-core.c | 12 ++++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
index 5ca6278baff4..09f75dffae60 100644
--- a/drivers/hwtracing/coresight/coresight-etm-perf.c
+++ b/drivers/hwtracing/coresight/coresight-etm-perf.c

@@ -68,6 +68,7 @@ PMU_FORMAT_ATTR(preset,               "config:0-3");
 PMU_FORMAT_ATTR(sinkid,                "config2:0-31");
 /* config ID - set if a system configuration is selected */
 PMU_FORMAT_ATTR(configid,      "config2:32-63");
+PMU_FORMAT_ATTR(cc_threshold,  "config3:0-11");


 /*

@@ -101,6 +102,7 @@ static struct attribute *etm_config_formats_attr[] = {
        &format_attr_preset.attr,
        &format_attr_configid.attr,
        &format_attr_branch_broadcast.attr,
+       &format_attr_cc_threshold.attr,
        NULL,
 };

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 1f3d29a639ff..ad28ee044cba 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c

@@ -644,7 +644,7 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
        struct etmv4_config *config = &drvdata->config;
        struct perf_event_attr *attr = &event->attr;
        unsigned long cfg_hash;
-       int preset;
+       int preset, cc_threshold;

        /* Clear configuration from previous run */
        memset(config, 0, sizeof(struct etmv4_config));

@@ -667,7 +667,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
        if (attr->config & BIT(ETM_OPT_CYCACC)) {
                config->cfg |= TRCCONFIGR_CCI;
                /* TRM: Must program this for cycacc to work */
-               config->ccctlr = ETM_CYC_THRESHOLD_DEFAULT;
+               cc_threshold = attr->config3 & ETM_CYC_THRESHOLD_MASK;
+               if (cc_threshold) {
+                       if (cc_threshold < drvdata->ccitmin)
+                               config->ccctlr = drvdata->ccitmin;
+                       else
+                               config->ccctlr = cc_threshold;
+               } else {
+                       config->ccctlr = ETM_CYC_THRESHOLD_DEFAULT;

Don't normally have {} round a single statement else clause - did

I would believe single statement else clause could have { }, only
when the preceding if clause consists of multiple statements just
to be symmetrical ? 

checkpatch.pl not object here?

No, it does not object.

Otherwise

Reviewed-by: Mike Leach <redacted>

quoted

+               }
        }
        if (attr->config & BIT(ETM_OPT_TS)) {
                /*
--
2.25.1