From 9cc63f8bcd560c760d0b12e15bba8f81c86237cf Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@kernel.org>
Date: Fri, 14 Aug 2026 15:43:51 -0700
Subject: Merge branches 'expcb.2026.07.24a', 'misc.2026.07.30a',
 'rcu-tasks.2026.07.30a', 'srcu.2026.08.11a' and 'torture.2026.08.14a' into
 HEAD

Changes:

Make expedited grace periods expedite normal RCU callbacks

Miscellaneous fixes:
 * Improve diagnostic output with character task states.
 * Mark accesses to inform KCSAN of concurrency design.
 * Move from kmalloc() to kmalloc_obj().
 * Documentation updates.
 * Improve handling of RCU deferred quiescent states.
 * Clean up unused function arguments and structure fields.
 * Reduce show_rcu_gp_kthreads() stack space.

Tasks RCU updates:
 * Clean up after SRCU re-implementation of Tasks Trace RCU.
 * Mark accesses to inform KCSAN of concurrency design.
 * Add ->lazy_timer status to diagnostic output.
 * Remove an unnecessary memory barrier.
 * Fix a data race, courtesy of KCSAN.
 * Documentation updates.
 * Convert cond_resched_tasks_rcu_qs() from macro to static inline
   function.

SRCU updates:
 * Add Rust helpers for SRCU.
 * Avoid losing queued work at cleanup_srcu_struct() time.

Torture-test updates:
 * Preparation work for immediate RCU priority deboosting.
 * Test RCU readers from real interrupt handlers (as opposed to softirq).
 * Simplify code through use of cpumask_next_wrap().
 * Improve diagnostic output with character task states.
 * Add rcutorture.nwriters parameter to allow lightweight stall testing,
   and rcutorture.stall_only to make doing so easier.
 * Test an RCU Tasks Trace grace period implying an RCU grace period.
 * Make RCU Tasks Trace torturing track reader batches.
 * Fix a data race, courtesy of KCSAN.
 * Plug a shuffle_tmp_mask memory leak on kthread spawn failure.
---
 Documentation/driver-api/hte/hte.rst       | 79 ++++++++++++++++++++++++++++++
 Documentation/driver-api/hte/index.rst     | 22 +++++++++
 Documentation/driver-api/hte/tegra-hte.rst | 47 ++++++++++++++++++
 3 files changed, 148 insertions(+)
 create mode 100644 Documentation/driver-api/hte/hte.rst
 create mode 100644 Documentation/driver-api/hte/index.rst
 create mode 100644 Documentation/driver-api/hte/tegra-hte.rst

(limited to 'Documentation/driver-api/hte')

diff --git a/Documentation/driver-api/hte/hte.rst b/Documentation/driver-api/hte/hte.rst
new file mode 100644
index 000000000..153f3233c
--- /dev/null
+++ b/Documentation/driver-api/hte/hte.rst
@@ -0,0 +1,79 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+============================================
+The Linux Hardware Timestamping Engine (HTE)
+============================================
+
+:Author: Dipen Patel
+
+Introduction
+------------
+
+Certain devices have built in hardware timestamping engines which can
+monitor sets of system signals, lines, buses etc... in realtime for state
+change; upon detecting the change they can automatically store the timestamp at
+the moment of occurrence. Such functionality may help achieve better accuracy
+in obtaining timestamps than using software counterparts i.e. ktime and
+friends.
+
+This document describes the API that can be used by hardware timestamping
+engine provider and consumer drivers that want to use the hardware timestamping
+engine (HTE) framework. Both consumers and providers must include
+``#include <linux/hte.h>``.
+
+The HTE framework APIs for the providers
+----------------------------------------
+
+.. kernel-doc:: drivers/hte/hte.c
+   :functions: devm_hte_register_chip hte_push_ts_ns
+
+The HTE framework APIs for the consumers
+----------------------------------------
+
+.. kernel-doc:: drivers/hte/hte.c
+   :functions: hte_init_line_attr hte_ts_get hte_ts_put devm_hte_request_ts_ns hte_request_ts_ns hte_enable_ts hte_disable_ts of_hte_req_count hte_get_clk_src_info
+
+The HTE framework public structures
+-----------------------------------
+.. kernel-doc:: include/linux/hte.h
+
+More on the HTE timestamp data
+------------------------------
+The ``struct hte_ts_data`` is used to pass timestamp details between the
+consumers and the providers. It expresses timestamp data in nanoseconds in
+u64. An example of the typical timestamp data life cycle, for the GPIO line is
+as follows::
+
+ - Monitors GPIO line change.
+ - Detects the state change on GPIO line.
+ - Converts timestamps in nanoseconds.
+ - Stores GPIO raw level in raw_level variable if the provider has that
+ hardware capability.
+ - Pushes this hte_ts_data object to HTE subsystem.
+ - HTE subsystem increments seq counter and invokes consumer provided callback.
+ Based on callback return value, the HTE core invokes secondary callback in
+ the thread context.
+
+HTE subsystem debugfs attributes
+--------------------------------
+HTE subsystem creates debugfs attributes at ``/sys/kernel/debug/hte/``.
+It also creates line/signal-related debugfs attributes at
+``/sys/kernel/debug/hte/<provider>/<label or line id>/``. Note that these
+attributes are read-only.
+
+`ts_requested`
+		The total number of entities requested from the given provider,
+		where entity is specified by the provider and could represent
+		lines, GPIO, chip signals, buses etc...
+                The attribute will be available at
+		``/sys/kernel/debug/hte/<provider>/``.
+
+`total_ts`
+		The total number of entities supported by the provider.
+                The attribute will be available at
+		``/sys/kernel/debug/hte/<provider>/``.
+
+`dropped_timestamps`
+		The dropped timestamps for a given line.
+                The attribute will be available at
+		``/sys/kernel/debug/hte/<provider>/<label or line id>/``.
diff --git a/Documentation/driver-api/hte/index.rst b/Documentation/driver-api/hte/index.rst
new file mode 100644
index 000000000..29011de9a
--- /dev/null
+++ b/Documentation/driver-api/hte/index.rst
@@ -0,0 +1,22 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+============================================
+The Linux Hardware Timestamping Engine (HTE)
+============================================
+
+The HTE Subsystem
+=================
+
+.. toctree::
+   :maxdepth: 1
+
+   hte
+
+HTE Tegra Provider
+==================
+
+.. toctree::
+   :maxdepth: 1
+
+   tegra-hte
+
diff --git a/Documentation/driver-api/hte/tegra-hte.rst b/Documentation/driver-api/hte/tegra-hte.rst
new file mode 100644
index 000000000..85e654772
--- /dev/null
+++ b/Documentation/driver-api/hte/tegra-hte.rst
@@ -0,0 +1,47 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+HTE Kernel provider driver
+==========================
+
+Description
+-----------
+The Nvidia tegra HTE provider also known as GTE (Generic Timestamping Engine)
+driver implements two GTE instances: 1) GPIO GTE and 2) LIC
+(Legacy Interrupt Controller) IRQ GTE. Both GTE instances get the timestamp
+from the system counter TSC which has 31.25MHz clock rate, and the driver
+converts clock tick rate to nanoseconds before storing it as timestamp value.
+
+GPIO GTE
+--------
+
+This GTE instance timestamps GPIO in real time. For that to happen GPIO
+needs to be configured as input. Only the always on (AON) GPIO controller
+instance supports timestamping GPIOs in real time as it is tightly coupled with
+the GPIO GTE. To support this, GPIOLIB adds two optional APIs as mentioned
+below. The GPIO GTE code supports both kernel and userspace consumers. The
+kernel space consumers can directly talk to HTE subsystem while userspace
+consumers timestamp requests go through GPIOLIB CDEV framework to HTE
+subsystem. The hte devicetree binding described at
+``Documentation/devicetree/bindings/timestamp`` provides an example of how a
+consumer can request an GPIO line.
+
+See gpiod_enable_hw_timestamp_ns() and gpiod_disable_hw_timestamp_ns().
+
+For userspace consumers, GPIO_V2_LINE_FLAG_EVENT_CLOCK_HTE flag must be
+specified during IOCTL calls. Refer to ``tools/gpio/gpio-event-mon.c``, which
+returns the timestamp in nanoseconds.
+
+LIC (Legacy Interrupt Controller) IRQ GTE
+-----------------------------------------
+
+This GTE instance timestamps LIC IRQ lines in real time. The hte devicetree
+binding described at ``Documentation/devicetree/bindings/timestamp``
+provides an example of how a consumer can request an IRQ line. Since it is a
+one-to-one mapping with IRQ GTE provider, consumers can simply specify the IRQ
+number that they are interested in. There is no userspace consumer support for
+this GTE instance in the HTE framework.
+
+The provider source code of both IRQ and GPIO GTE instances is located at
+``drivers/hte/hte-tegra194.c``. The test driver
+``drivers/hte/hte-tegra194-test.c`` demonstrates HTE API usage for both IRQ
+and GPIO GTE.
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