linux-kernel - Re: [PATCH v4 13/13] coresight: docs: Document etm4x timestamp interval option

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Message-ID: <0eb1a2b7-8064-4ac5-bcf8-b4898a8b5ac7@infradead.org>
Date: Thu, 13 Nov 2025 21:02:13 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: James Clark <james.clark@...aro.org>,
 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
Subject: Re: [PATCH v4 13/13] coresight: docs: Document etm4x timestamp
 interval option



On 11/12/25 7:22 AM, 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@...aro.org>
> ---
>  Documentation/trace/coresight/coresight.rst | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/trace/coresight/coresight.rst b/Documentation/trace/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_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 = maximum interval .. 15 = 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 raised to
> +       the power of timestamp 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.

	  value = 11: 2^11-1 = 2047

Maybe add some parens?


-- 
~Randy