tegra194-hte.rst (2229B)
1.. SPDX-License-Identifier: GPL-2.0+ 2 3HTE Kernel provider driver 4========================== 5 6Description 7----------- 8The Nvidia tegra194 HTE provider driver implements two GTE 9(Generic Timestamping Engine) instances: 1) GPIO GTE and 2) LIC 10(Legacy Interrupt Controller) IRQ GTE. Both GTE instances get the 11timestamp from the system counter TSC which has 31.25MHz clock rate, and the 12driver converts clock tick rate to nanoseconds before storing it as timestamp 13value. 14 15GPIO GTE 16-------- 17 18This GTE instance timestamps GPIO in real time. For that to happen GPIO 19needs to be configured as input. The always on (AON) GPIO controller instance 20supports timestamping GPIOs in real time and it has 39 GPIO lines. The GPIO GTE 21and AON GPIO controller are tightly coupled as it requires very specific bits 22to be set in GPIO config register before GPIO GTE can be used, for that GPIOLIB 23adds two optional APIs as below. The GPIO GTE code supports both kernel 24and userspace consumers. The kernel space consumers can directly talk to HTE 25subsystem while userspace consumers timestamp requests go through GPIOLIB CDEV 26framework to HTE subsystem. 27 28.. kernel-doc:: drivers/gpio/gpiolib.c 29 :functions: gpiod_enable_hw_timestamp_ns gpiod_disable_hw_timestamp_ns 30 31For userspace consumers, GPIO_V2_LINE_FLAG_EVENT_CLOCK_HTE flag must be 32specified during IOCTL calls. Refer to ``tools/gpio/gpio-event-mon.c``, which 33returns the timestamp in nanoseconds. 34 35LIC (Legacy Interrupt Controller) IRQ GTE 36----------------------------------------- 37 38This GTE instance timestamps LIC IRQ lines in real time. There are 352 IRQ 39lines which this instance can add timestamps to in real time. The hte 40devicetree binding described at ``Documentation/devicetree/bindings/hte/`` 41provides an example of how a consumer can request an IRQ line. Since it is a 42one-to-one mapping with IRQ GTE provider, consumers can simply specify the IRQ 43number that they are interested in. There is no userspace consumer support for 44this GTE instance in the HTE framework. 45 46The provider source code of both IRQ and GPIO GTE instances is located at 47``drivers/hte/hte-tegra194.c``. The test driver 48``drivers/hte/hte-tegra194-test.c`` demonstrates HTE API usage for both IRQ 49and GPIO GTE.