| .. 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. |
