coresight: etm-perf: Clarify comment on perf options

In theory, the options should be arbitrary values and are neutral for
any ETM version; so far perf tool uses ETMv3.5/PTM ETMCR config bits
except for register's bit definitions, also uses as options.

This can introduce confusion, especially if we want to add a new option
but the new option is not supported by ETMv3.5/PTM ETMCR.  But on the
other hand, we cannot change options since these options are generic
CoreSight PMU ABI.

For easier maintenance and avoid confusion, this patch refines the
comment to clarify perf options, and gives out the background info for
these bits are coming from ETMv3.5/PTM.  Afterwards, we should take
these options as general knobs, and if there have any confliction with
ETMv3.5/PTM, should consider to define saperate macros for ETMv3.5/PTM
ETMCR config bits.

Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20210206150833.42120-2-leo.yan@linaro.org
Link: https://lore.kernel.org/r/20210211172038.2483517-2-mathieu.poirier@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
index bdc34ca449f7145ba06755738e4e97029310564f..465ef1aa8c82598e11ea95a4534324ab549f06f7 100644 (file)
--- a/drivers/hwtracing/coresight/coresight-etm-perf.c
+++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
@@ -27,7 +27,10 @@ static bool etm_perf_up;
 static DEFINE_PER_CPU(struct perf_output_handle, ctx_handle);
 static DEFINE_PER_CPU(struct coresight_device *, csdev_src);
 
-/* ETMv3.5/PTM's ETMCR is 'config' */
+/*
+ * 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(cycacc,                "config:" __stringify(ETM_OPT_CYCACC));
 PMU_FORMAT_ATTR(contextid,     "config:" __stringify(ETM_OPT_CTXTID));
 PMU_FORMAT_ATTR(timestamp,     "config:" __stringify(ETM_OPT_TS));

diff --git a/include/linux/coresight-pmu.h b/include/linux/coresight-pmu.h
index b0e35eec6499bf4367da462c1f180c77821336e2..5dc47cfdcf07533585969bc7ad2a6f2fe337be50 100644 (file)
--- a/include/linux/coresight-pmu.h
+++ b/include/linux/coresight-pmu.h
@@ -10,11 +10,18 @@
 #define CORESIGHT_ETM_PMU_NAME "cs_etm"
 #define CORESIGHT_ETM_PMU_SEED  0x10
 
-/* ETMv3.5/PTM's ETMCR config bit */
-#define ETM_OPT_CYCACC  12
-#define ETM_OPT_CTXTID 14
-#define ETM_OPT_TS      28
-#define ETM_OPT_RETSTK 29
+/*
+ * Below are the definition of bit offsets for perf option, and works as
+ * arbitrary values for all ETM versions.
+ *
+ * Most of them are orignally from ETMv3.5/PTM's ETMCR config, therefore,
+ * ETMv3.5/PTM doesn't define ETMCR config bits with prefix "ETM3_" and
+ * directly use below macros as config bits.
+ */
+#define ETM_OPT_CYCACC         12
+#define ETM_OPT_CTXTID         14
+#define ETM_OPT_TS             28
+#define ETM_OPT_RETSTK         29
 
 /* ETMv4 CONFIGR programming bits for the ETM OPTs */
 #define ETM4_CFG_BIT_CYCACC    4