linux-kernel - [PATCH v3 0/5] coresight: Add format attribute for setting the timestamp interval

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Message-Id: <20251002-james-cs-syncfreq-v3-0-fe5df2bf91d1@linaro.org>
Date: Thu, 02 Oct 2025 11:09:28 +0100
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>
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 v3 0/5] coresight: Add format attribute for setting the
 timestamp interval

Do some cleanups then add a new format attribute to set the timestamp
interval for ETMv4 in Perf mode. The current interval is too high for
most use cases, and particularly on the FVP the number of timestamps
generated is excessive.

Although it would be good to make only SYNC timestamps the default and
have counter timestamps opt-in, this would be a breaking change. We
can always do that later, or disable counter timestamps from Perf.

This is added as an event format attribute, rather than a Coresight
config because it's something that the driver is already configuring
automatically in Perf mode with any unused counter, so it's not possible
to modify this with a config.

Applies to coresight/next

Signed-off-by: James Clark <james.clark@...aro.org>
---
Changes in v3:
- Move the format attr definitions to coresight-etm-perf.h we can
  compile on arm32 without #ifdefs - (Leo)
- Convert the new #ifdefs to a single one in an is_visible() function so
  that the code is cleaner - (Leo)
- Drop the change to remove the holes in struct etmv4_config as they
  were grouped by function - (Mike)
- Link to v2: https://lore.kernel.org/r/20250814-james-cs-syncfreq-v2-0-c76fcb87696d@linaro.org

Changes in v2:
- Only show the attribute for ETMv4 to improve usability and fix the
  arm32 build error. Wrapping everything in
  IS_ENABLED(CONFIG_CORESIGHT_SOURCE_ETM4X) isn't ideal, but the -perf.c
  file is shared between ETMv3 and ETMv4, and there is already precedent
  for doing it this way.
- Link to v1: https://lore.kernel.org/r/20250811-james-cs-syncfreq-v1-0-b001cd6e3404@linaro.org

---
James Clark (5):
      coresight: Change syncfreq to be a u8
      coresight: Repack struct etmv4_drvdata
      coresight: Refactor etm4_config_timestamp_event()
      coresight: Add format attribute for setting the timestamp interval
      coresight: docs: Document etm4x ts_interval

 Documentation/trace/coresight/coresight.rst        |  14 +++
 drivers/hwtracing/coresight/coresight-etm-perf.c   |  16 ++-
 drivers/hwtracing/coresight/coresight-etm-perf.h   |   7 ++
 drivers/hwtracing/coresight/coresight-etm4x-core.c | 110 +++++++++++++--------
 drivers/hwtracing/coresight/coresight-etm4x.h      |  61 +++++++-----
 5 files changed, 143 insertions(+), 65 deletions(-)
---
base-commit: 01f96b812526a2c8dcd5c0e510dda37e09ec8bcd
change-id: 20250724-james-cs-syncfreq-7c2257a38ed3

Best regards,
-- 
James Clark <james.clark@...aro.org>