[PATCH v6 01/10] Documentation: Add HTE subsystem guide

[Dipen Patel <dipenp@nvidia.com>]

Adding hte document which can help understand various APIs implemented
in HTE framework for the HTE producers and the consumers.

Signed-off-by: Dipen Patel <dipenp@nvidia.com>
---
Changes in v2:
- Removed explanation, instead added kernel-doc references.

Changes in v3:
- Addressed grammatical errors.

Changes in v4:
- Added new API hte_req_ts_by_linedata_ns description.
- Removed hte_req_ts_by_hte_name.

Changes in v6:
- Added hte_init_line_attr, hte_ts_get, of_hte_req_count.
- Removed devm_of_hte_request_ts_ns, hte_req_ts_by_linedata_ns, hte_release_ts.
- Replaced above with devm_hte_request_ts_ns, hte_request_ts_ns, hte_ts_put.
- Addressed review comments.

 Documentation/hte/hte.rst | 77 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 Documentation/hte/hte.rst

diff --git a/Documentation/hte/hte.rst b/Documentation/hte/hte.rst
new file mode 100644
index 000000000000..75100a9bc35f
--- /dev/null
+++ b/Documentation/hte/hte.rst
@@ -0,0 +1,77 @@
+============================================
+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>/``.
-- 
2.17.1