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From:   Kurt Kanzenbach <kurt@linutronix.de>
To:     John Stultz <john.stultz@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Stephen Boyd <sboyd@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>
Cc:     Richard Cochran <richardcochran@gmail.com>,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        Kurt Kanzenbach <kurt@linutronix.de>
Subject: [PATCH v2 3/3] tracing: Add documentation for trace clock tai
Date:   Thu, 14 Apr 2022 11:18:05 +0200
Message-Id: <20220414091805.89667-4-kurt@linutronix.de>
In-Reply-To: <20220414091805.89667-1-kurt@linutronix.de>
References: <20220414091805.89667-1-kurt@linutronix.de>
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Add documentation for newly introduced trace clock "tai".
This clock corresponds to CLOCK_TAI.

Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
---
 Documentation/trace/ftrace.rst | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index 45b8c56af67a..b37dc19e4d40 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -517,6 +517,18 @@ of ftrace. Here is a list of some of the key files:
 		processing should be able to handle them. See comments in the
 		ktime_get_boot_fast_ns() function for more information.
 
+	tai:
+		This is the tai clock (CLOCK_TAI) and is derived from the wall-
+		clock time. However, this clock does not experience
+		discontinuities and backwards jumps caused by NTP inserting leap
+		seconds. Since the clock access is designed for use in tracing,
+		side effects are possible. The clock access may yield wrong
+		readouts in case the internal TAI offset is updated e.g., caused
+		by setting the system time or using adjtimex() with an offset.
+		These effects are rare and post processing should be able to
+		handle them. See comments in the ktime_get_tai_fast_ns()
+		function for more information.
+
 	To set a clock, simply echo the clock name into this file::
 
 	  # echo global > trace_clock
-- 
2.30.2