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@xxxxxxxxxx> --- Changes in v2: - Removed explanation, instead added kernel-doc references. Changes in v3: - Addressed grammatical errors. Documentation/hte/hte.rst | 84 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 84 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..c39e57303d12 --- /dev/null +++ b/Documentation/hte/hte.rst @@ -0,0 +1,84 @@ +============================================ +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 <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: devm_of_hte_request_ts hte_req_ts_by_hte_name hte_release_ts hte_enable_ts hte_disable_ts 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 data +type. For now all the HTE APIs using struct hte_ts_data require tsc to be in +nanoseconds. An example of the typical hte_ts_data 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 and stores it in tsc. + - Stores GPIO direction in dir 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 starts a kernel thread and 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>/``. + +`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>/``. + + Read-only value + +`total_ts` + The total number of entities supported by the provider. + The attribute will be available at + ``/sys/kernel/debug/hte/<provider>/``. + + Read-only value + +`dropped_timestamps` + The dropped timestamps for a given line. + The attribute will be available at + ``/sys/kernel/debug/hte/<provider>/<label or line id>/``. + + Read-only value -- 2.17.1
