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