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Message-Id: <20251126-james-cs-syncfreq-v7-3-7fae5e0e5e16@linaro.org>
Date: Wed, 26 Nov 2025 10:54:32 +0000
From: James Clark <james.clark@...aro.org>
To: Suzuki K Poulose <suzuki.poulose@....com>,
Mike Leach <mike.leach@...aro.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jonathan Corbet <corbet@....net>, Leo Yan <leo.yan@....com>,
Randy Dunlap <rdunlap@...radead.org>
Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
James Clark <james.clark@...aro.org>
Subject: [PATCH v7 03/13] coresight: Refactor etm4_config_timestamp_event()
Remove some of the magic numbers and try to clarify some of the
documentation so it's clearer how this sets up the timestamp interval.
Return errors directly instead of jumping to out and returning ret,
nothing needs to be cleaned up at the end and it only obscures the flow
and return value.
Add utilities for programming resource selectors that do compile time
checks for constants or WARN_ONs for non-constant values. FIELD_PREP
includes compile time checks so we only need to add an additional
BUILD_BUG_ON for resource == 0 in pair mode.
Signed-off-by: James Clark <james.clark@...aro.org>
---
drivers/hwtracing/coresight/coresight-etm4x-core.c | 96 ++++++++++++++--------
drivers/hwtracing/coresight/coresight-etm4x.h | 54 ++++++++++--
2 files changed, 112 insertions(+), 38 deletions(-)
diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 560975b70474..2ec2ae1fef58 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -642,18 +642,33 @@ static void etm4_enable_sysfs_smp_call(void *info)
* 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.
+ * event that will insert a timestamp packet in the stream:
+ *
+ * +--------------+
+ * | Resource 1 | fixed "always-true" resource
+ * +--------------+
+ * |
+ * +------v-------+
+ * | Counter x | (reload to 1 on underflow)
+ * +--------------+
+ * |
+ * +------v--------------+
+ * | Resource Selector y | (trigger on counter x == 0)
+ * +---------------------+
+ * |
+ * +------v---------------+
+ * | Timestamp Generator | (timestamp on resource y)
+ * +----------------------+
*/
static int etm4_config_timestamp_event(struct etmv4_drvdata *drvdata)
{
- int ctridx, ret = -EINVAL;
- int counter, rselector;
- u32 val = 0;
+ int ctridx;
+ int rselector;
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;
+ return -EINVAL;
/* Find a counter that hasn't been initialised */
for (ctridx = 0; ctridx < drvdata->nr_cntr; ctridx++)
@@ -663,15 +678,19 @@ static int etm4_config_timestamp_event(struct etmv4_drvdata *drvdata)
/* 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;
+ return -ENOSPC;
}
/*
- * 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.
+ * Searching for an available resource selector to use, starting at '2'
+ * since resource 0 is the fixed 'always returns false' resource and 1
+ * is the fixed 'always returns true' resource. See IHI0064H_b '7.3.64
+ * TRCRSCTLRn, Resource Selection Control Registers, n=2-31'. If there
+ * are no resources, there would also be no counters so wouldn't get
+ * here.
+ *
+ * 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])
@@ -680,13 +699,9 @@ static int etm4_config_timestamp_event(struct etmv4_drvdata *drvdata)
if (rselector == drvdata->nr_resource * 2) {
pr_debug("%s: no available resource selector found\n",
__func__);
- ret = -ENOSPC;
- goto out;
+ return -ENOSPC;
}
- /* 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.
@@ -694,26 +709,41 @@ static int etm4_config_timestamp_event(struct etmv4_drvdata *drvdata)
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;
+ /*
+ * Trace Counter Control Register TRCCNTCTLRn
+ *
+ * CNTCHAIN = 0, don't reload on the previous counter
+ * RLDSELF = true, reload counter automatically on underflow
+ * RLDEVENT = RES_SEL_FALSE (0), reload on single false resource (never reload)
+ * CNTEVENT = RES_SEL_TRUE (1), count single fixed 'always true' resource (always decrement)
+ */
+ config->cntr_ctrl[ctridx] = TRCCNTCTLRn_RLDSELF |
+ FIELD_PREP(TRCCNTCTLRn_RLDEVENT_MASK,
+ etm4_res_sel_single(ETM4_RES_SEL_FALSE)) |
+ FIELD_PREP(TRCCNTCTLRn_CNTEVENT_MASK,
+ etm4_res_sel_single(ETM4_RES_SEL_TRUE));
- val = 0x0 << 7 | /* Select single resource selector */
- rselector; /* Resource selector */
+ /*
+ * Resource Selection Control Register TRCRSCTLRn
+ *
+ * PAIRINV = 0, INV = 0, don't invert
+ * GROUP = 2, SELECT = ctridx, trigger when counter 'ctridx' reaches 0
+ *
+ * Multiple counters can be selected, and each bit signifies a counter,
+ * so set bit 'ctridx' to select our counter.
+ */
+ config->res_ctrl[rselector] = FIELD_PREP(TRCRSCTLRn_GROUP_MASK, 2) |
+ FIELD_PREP(TRCRSCTLRn_SELECT_MASK, 1 << ctridx);
- config->ts_ctrl = val;
+ /*
+ * Global Timestamp Control Register TRCTSCTLR
+ *
+ * EVENT = generate timestamp on single resource 'rselector'
+ */
+ config->ts_ctrl = FIELD_PREP(TRCTSCTLR_EVENT_MASK,
+ etm4_res_sel_single(rselector));
- ret = 0;
-out:
- return ret;
+ return 0;
}
static int etm4_parse_event_config(struct coresight_device *csdev,
diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
index d178d79d9827..89d81ce4e04e 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x.h
+++ b/drivers/hwtracing/coresight/coresight-etm4x.h
@@ -225,6 +225,50 @@
#define TRCRSCTLRn_GROUP_MASK GENMASK(19, 16)
#define TRCRSCTLRn_SELECT_MASK GENMASK(15, 0)
+#define TRCCNTCTLRn_CNTCHAIN BIT(17)
+#define TRCCNTCTLRn_RLDSELF BIT(16)
+#define TRCCNTCTLRn_RLDEVENT_MASK GENMASK(15, 8)
+#define TRCCNTCTLRn_CNTEVENT_MASK GENMASK(7, 0)
+
+#define TRCTSCTLR_EVENT_MASK GENMASK(7, 0)
+
+#define ETM4_RES_SEL_FALSE 0 /* Fixed function 'always false' resource selector */
+#define ETM4_RES_SEL_TRUE 1 /* Fixed function 'always true' resource selector */
+
+#define ETM4_RES_SEL_SINGLE_MASK GENMASK(4, 0)
+#define ETM4_RES_SEL_PAIR_MASK GENMASK(3, 0)
+#define ETM4_RES_SEL_TYPE_PAIR BIT(7)
+
+/*
+ * Utilities for programming EVENT resource selectors, e.g. TRCCNTCTLRn_RLDEVENT.
+ *
+ * Resource selectors have a common format across registers:
+ *
+ * 7 6 5 4 0
+ * +------+------+-------+
+ * | TYPE | RES0 | SEL |
+ * +------+------+-------+
+ *
+ * Where TYPE indicates whether the selector is for a single event or a pair.
+ * When TYPE is pair, SEL is 4 bits wide and using pair 0 is UNPREDICTABLE.
+ * Otherwise for single it's 5 bits wide.
+ */
+static inline u32 etm4_res_sel_single(u8 res_sel_idx)
+{
+ WARN_ON_ONCE(!FIELD_FIT(ETM4_RES_SEL_SINGLE_MASK, res_sel_idx));
+ return FIELD_PREP(ETM4_RES_SEL_SINGLE_MASK, res_sel_idx);
+}
+
+static inline u32 etm4_res_sel_pair(u8 res_sel_idx)
+{
+ if (__builtin_constant_p(res_sel_idx))
+ BUILD_BUG_ON(res_sel_idx == 0);
+ WARN_ON_ONCE(!FIELD_FIT(ETM4_RES_SEL_PAIR_MASK, res_sel_idx) ||
+ (res_sel_idx == 0));
+ return FIELD_PREP(ETM4_RES_SEL_PAIR_MASK, res_sel_idx) |
+ ETM4_RES_SEL_TYPE_PAIR;
+}
+
/*
* System instructions to access ETM registers.
* See ETMv4.4 spec ARM IHI0064F section 4.3.6 System instructions
@@ -824,7 +868,7 @@ struct etmv4_config {
u32 eventctrl0;
u32 eventctrl1;
u32 stall_ctrl;
- u32 ts_ctrl;
+ u32 ts_ctrl; /* TRCTSCTLR */
u32 ccctlr;
u32 bb_ctrl;
u32 vinst_ctrl;
@@ -837,11 +881,11 @@ struct etmv4_config {
u32 seq_rst;
u32 seq_state;
u8 cntr_idx;
- u32 cntrldvr[ETMv4_MAX_CNTR];
- u32 cntr_ctrl[ETMv4_MAX_CNTR];
- u32 cntr_val[ETMv4_MAX_CNTR];
+ u32 cntrldvr[ETMv4_MAX_CNTR]; /* TRCCNTRLDVRn */
+ u32 cntr_ctrl[ETMv4_MAX_CNTR]; /* TRCCNTCTLRn */
+ u32 cntr_val[ETMv4_MAX_CNTR]; /* TRCCNTVRn */
u8 res_idx;
- u32 res_ctrl[ETM_MAX_RES_SEL];
+ u32 res_ctrl[ETM_MAX_RES_SEL]; /* TRCRSCTLRn */
u8 ss_idx;
u32 ss_ctrl[ETM_MAX_SS_CMP];
u32 ss_status[ETM_MAX_SS_CMP];
--
2.34.1
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