linux-kernel - [PATCH 6/6] coresight: docs: Document etm4x ts

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Message-Id: <20250811-james-cs-syncfreq-v1-6-b001cd6e3404@linaro.org>
Date: Mon, 11 Aug 2025 10:32:11 +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 6/6] coresight: docs: Document etm4x ts_interval

Document how the new field is used, maximum value and the interaction
with SYNC timestamps.

Signed-off-by: James Clark <james.clark@...aro.org>
---
 Documentation/trace/coresight/coresight.rst | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/Documentation/trace/coresight/coresight.rst b/Documentation/trace/coresight/coresight.rst
index 806699871b80..0cd83119b83f 100644
--- a/Documentation/trace/coresight/coresight.rst
+++ b/Documentation/trace/coresight/coresight.rst
@@ -619,6 +619,20 @@ They are also listed in the folder /sys/bus/event_source/devices/cs_etm/format/
      - Cycle count threshold value. If nothing is provided here or the provided value is 0, then the
        default value i.e 0x100 will be used. If provided value is less than minimum cycles threshold
        value, as indicated via TRCIDR3.CCITMIN, then the minimum value will be used instead.
+   * - ts_level
+     - Controls frequency of timestamps. The reload value of the
+       timestamp counter is 2 raised to the power of this value. If the value is
+       0 then the reload value is 1, if the value is 10 then the reload value is
+       1024. Maximum allowed value is 15, and setting the maximum disables
+       generation of timestamps via the counter, freeing the counter resources.
+       Timestamps will be generated after 2 ^ ts_level cycles.
+
+       Separately to this value, timestamps will also be emitted when a SYNC
+       packet is generated, although this is only for every 4096 bytes of trace.
+       Therefore it's not possible to generate timestamps less frequently than
+       that and ts_level timestamps are always in addition to SYNC timestamps.
+       Timestamps must be enabled for this to have effect.
+
 
 How to use the STM module
 -------------------------

-- 
2.34.1