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Subject[PATCH 16/32] coresight: etm4x: Configure tracers to emit timestamps
Date
Configure timestamps to be emitted at regular intervals in the trace
stream to temporally correlate instructions executed on different CPUs.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Tested-by: Leo Yan <leo.yan@linaro.org>
Tested-by: Robert Walker <robert.walker@arm.com>
---
drivers/hwtracing/coresight/coresight-etm4x.c | 102 +++++++++++++++++-
1 file changed, 101 insertions(+), 1 deletion(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c
index d64192c29860..8bb0092c7ec2 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x.c
@@ -204,6 +204,91 @@ static void etm4_enable_hw_smp_call(void *info)
arg->rc = etm4_enable_hw(arg->drvdata);
}

+/*
+ * The goal of function etm4_config_timestamp_event() is to configure a
+ * counter that will tell the tracer to emit a timestamp packet when it
+ * reaches zero. This is done in order to get a more fine grained idea
+ * of when instructions are executed so that they can be correlated
+ * with execution on other CPUs.
+ *
+ * To do this the counter itself is configured to self reload and
+ * TRCRSCTLR1 (always true) used to get the counter to decrement. From
+ * there a resource selector is configured with the counter and the
+ * timestamp control register to use the resource selector to trigger the
+ * event that will insert a timestamp packet in the stream.
+ */
+static int etm4_config_timestamp_event(struct etmv4_drvdata *drvdata)
+{
+ int ctridx, ret = -EINVAL;
+ int counter, rselector;
+ u32 val = 0;
+ struct etmv4_config *config = &drvdata->config;
+
+ /* No point in trying if we don't have at least one counter */
+ if (!drvdata->nr_cntr)
+ goto out;
+
+ /* Find a counter that hasn't been initialised */
+ for (ctridx = 0; ctridx < drvdata->nr_cntr; ctridx++)
+ if (config->cntr_val[ctridx] == 0)
+ break;
+
+ /* All the counters have been configured already, bail out */
+ if (ctridx == drvdata->nr_cntr) {
+ pr_debug("%s: no available counter found\n", __func__);
+ ret = -ENOSPC;
+ goto out;
+ }
+
+ /*
+ * Searching for an available resource selector to use, starting at
+ * '2' since every implementation has at least 2 resource selector.
+ * ETMIDR4 gives the number of resource selector _pairs_,
+ * hence multiply by 2.
+ */
+ for (rselector = 2; rselector < drvdata->nr_resource * 2; rselector++)
+ if (!config->res_ctrl[rselector])
+ break;
+
+ if (rselector == drvdata->nr_resource * 2) {
+ pr_debug("%s: no available resource selector found\n",
+ __func__);
+ ret = -ENOSPC;
+ goto out;
+ }
+
+ /* Remember what counter we used */
+ counter = 1 << ctridx;
+
+ /*
+ * Initialise original and reload counter value to the smallest
+ * possible value in order to get as much precision as we can.
+ */
+ config->cntr_val[ctridx] = 1;
+ config->cntrldvr[ctridx] = 1;
+
+ /* Set the trace counter control register */
+ val = 0x1 << 16 | /* Bit 16, reload counter automatically */
+ 0x0 << 7 | /* Select single resource selector */
+ 0x1; /* Resource selector 1, i.e always true */
+
+ config->cntr_ctrl[ctridx] = val;
+
+ val = 0x2 << 16 | /* Group 0b0010 - Counter and sequencers */
+ counter << 0; /* Counter to use */
+
+ config->res_ctrl[rselector] = val;
+
+ val = 0x0 << 7 | /* Select single resource selector */
+ rselector; /* Resource selector */
+
+ config->ts_ctrl = val;
+
+ ret = 0;
+out:
+ return ret;
+}
+
static int etm4_parse_event_config(struct etmv4_drvdata *drvdata,
struct perf_event *event)
{
@@ -239,9 +324,24 @@ static int etm4_parse_event_config(struct etmv4_drvdata *drvdata,
/* TRM: Must program this for cycacc to work */
config->ccctlr = ETM_CYC_THRESHOLD_DEFAULT;
}
- if (attr->config & BIT(ETM_OPT_TS))
+ if (attr->config & BIT(ETM_OPT_TS)) {
+ /*
+ * Configure timestamps to be emitted at regular intervals in
+ * order to correlate instructions executed on different CPUs
+ * (CPU-wide trace scenarios).
+ */
+ ret = etm4_config_timestamp_event(drvdata);
+
+ /*
+ * No need to go further if timestamp intervals can't
+ * be configured.
+ */
+ if (ret)
+ goto out;
+
/* bit[11], Global timestamp tracing bit */
config->cfg |= BIT(11);
+ }

if (attr->config & BIT(ETM_OPT_CTXTID))
/* bit[6], Context ID tracing bit */
--
2.17.1
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