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Wed, 12 Nov 2025 07:22:40 -0800 (PST) From: James Clark Date: Wed, 12 Nov 2025 15:22:19 +0000 Subject: [PATCH v4 13/13] coresight: docs: Document etm4x timestamp interval option Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20251112-james-cs-syncfreq-v4-13-165ba21401dc@linaro.org> References: <20251112-james-cs-syncfreq-v4-0-165ba21401dc@linaro.org> In-Reply-To: <20251112-james-cs-syncfreq-v4-0-165ba21401dc@linaro.org> To: Suzuki K Poulose , Mike Leach , Alexander Shishkin , Jonathan Corbet , Leo Yan Cc: coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, James Clark X-Mailer: b4 0.14.0 Document how the new field is used, maximum value and the interaction with SYNC timestamps. Signed-off-by: James Clark --- Documentation/trace/coresight/coresight.rst | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/Documentation/trace/coresight/coresight.rst b/Documentation/tr= ace/coresight/coresight.rst index 806699871b80..80b5ed09d69b 100644 --- a/Documentation/trace/coresight/coresight.rst +++ b/Documentation/trace/coresight/coresight.rst @@ -613,8 +613,19 @@ They are also listed in the folder /sys/bus/event_sour= ce/devices/cs_etm/format/ - Session local version of the system wide setting: :ref:`ETM_MODE_RE= TURNSTACK ` * - timestamp - - Session local version of the system wide setting: :ref:`ETMv4_MODE_= TIMESTAMP - ` + - Controls generation and interval of timestamps. + + 0 =3D off, 1 =3D maximum interval .. 15 =3D minimum interval. + + Values 1 - 14 use a counter that decrements every cycle to generate= a + timestamp on underflow. The reload value for the counter is 2 raise= d to + the power of timestamp interval - 1. If the value is 1 then the rel= oad + value is 1, if the value is 11 then the reload value is 1024 etc. + + Setting the minimum interval (15) will disable the counter generated + timestamps, freeing the counter resource, leaving only ones emitted= when + a SYNC packet is generated for every 4096 bytes of trace. + * - cc_threshold - Cycle count threshold value. If nothing is provided here or the pro= vided value is 0, then the default value i.e 0x100 will be used. If provided value is less tha= n minimum cycles threshold --=20 2.34.1