[PATCH v7 13/13] coresight: docs: Document etm4x timestamp interval option

[Leo Yan]

On Wed, Nov 26, 2025 at 10:54:42AM +0000, James Clark wrote:
> Document how the new field is used, maximum value and the interaction
> with SYNC timestamps.
> 
> Signed-off-by: James Clark <james.clark at linaro.org>

Reviewed-by: Leo Yan <leo.yan at arm.com>

> ---
>  Documentation/trace/coresight/coresight.rst | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/trace/coresight/coresight.rst b/Documentation/trace/coresight/coresight.rst
> index 806699871b80..d461de4e067e 100644
> --- a/Documentation/trace/coresight/coresight.rst
> +++ b/Documentation/trace/coresight/coresight.rst
> @@ -613,8 +613,20 @@ They are also listed in the folder /sys/bus/event_source/devices/cs_etm/format/
>       - Session local version of the system wide setting: :ref:`ETM_MODE_RETURNSTACK
>         <coresight-return-stack>`
>     * - timestamp
> -     - Session local version of the system wide setting: :ref:`ETMv4_MODE_TIMESTAMP
> -       <coresight-timestamp>`
> +     - Controls generation and interval of timestamps.
> +
> +       0 = off, 1 = minimum interval .. 15 = maximum 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 ^ (interval
> +       - 1). If the value is 1 then the reload value is 1, if the value is 11
> +       then the reload value is 1024 etc.
> +
> +       Setting the maximum interval (15) will disable the counter generated
> +       timestamps, freeing the counter resource, leaving only ones emitted when
> +       a SYNC packet is generated. The sync interval is controlled with
> +       TRCSYNCPR.PERIOD which is every 4096 bytes of trace by default.
> +
>     * - cc_threshold
>       - 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
> 
> -- 
> 2.34.1
>