1 .. SPDX-License-Identifier: GPL-2.0+ 1 .. SPDX-License-Identifier: GPL-2.0+
2 2
3 HTE Kernel provider driver 3 HTE Kernel provider driver
4 ========================== 4 ==========================
5 5
6 Description 6 Description
7 ----------- 7 -----------
8 The Nvidia tegra HTE provider also known as GT 8 The Nvidia tegra HTE provider also known as GTE (Generic Timestamping Engine)
9 driver implements two GTE instances: 1) GPIO G 9 driver implements two GTE instances: 1) GPIO GTE and 2) LIC
10 (Legacy Interrupt Controller) IRQ GTE. Both GT 10 (Legacy Interrupt Controller) IRQ GTE. Both GTE instances get the timestamp
11 from the system counter TSC which has 31.25MHz 11 from the system counter TSC which has 31.25MHz clock rate, and the driver
12 converts clock tick rate to nanoseconds before 12 converts clock tick rate to nanoseconds before storing it as timestamp value.
13 13
14 GPIO GTE 14 GPIO GTE
15 -------- 15 --------
16 16
17 This GTE instance timestamps GPIO in real time 17 This GTE instance timestamps GPIO in real time. For that to happen GPIO
18 needs to be configured as input. Only the alwa 18 needs to be configured as input. Only the always on (AON) GPIO controller
19 instance supports timestamping GPIOs in real t 19 instance supports timestamping GPIOs in real time as it is tightly coupled with
20 the GPIO GTE. To support this, GPIOLIB adds tw 20 the GPIO GTE. To support this, GPIOLIB adds two optional APIs as mentioned
21 below. The GPIO GTE code supports both kernel 21 below. The GPIO GTE code supports both kernel and userspace consumers. The
22 kernel space consumers can directly talk to HT 22 kernel space consumers can directly talk to HTE subsystem while userspace
23 consumers timestamp requests go through GPIOLI 23 consumers timestamp requests go through GPIOLIB CDEV framework to HTE
24 subsystem. The hte devicetree binding describe 24 subsystem. The hte devicetree binding described at
25 ``Documentation/devicetree/bindings/timestamp` 25 ``Documentation/devicetree/bindings/timestamp`` provides an example of how a
26 consumer can request an GPIO line. 26 consumer can request an GPIO line.
27 27
28 See gpiod_enable_hw_timestamp_ns() and gpiod_d 28 See gpiod_enable_hw_timestamp_ns() and gpiod_disable_hw_timestamp_ns().
29 29
30 For userspace consumers, GPIO_V2_LINE_FLAG_EVE 30 For userspace consumers, GPIO_V2_LINE_FLAG_EVENT_CLOCK_HTE flag must be
31 specified during IOCTL calls. Refer to ``tools 31 specified during IOCTL calls. Refer to ``tools/gpio/gpio-event-mon.c``, which
32 returns the timestamp in nanoseconds. 32 returns the timestamp in nanoseconds.
33 33
34 LIC (Legacy Interrupt Controller) IRQ GTE 34 LIC (Legacy Interrupt Controller) IRQ GTE
35 ----------------------------------------- 35 -----------------------------------------
36 36
37 This GTE instance timestamps LIC IRQ lines in 37 This GTE instance timestamps LIC IRQ lines in real time. The hte devicetree
38 binding described at ``Documentation/devicetre 38 binding described at ``Documentation/devicetree/bindings/timestamp``
39 provides an example of how a consumer can requ 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, cons 40 one-to-one mapping with IRQ GTE provider, consumers can simply specify the IRQ
41 number that they are interested in. There is n 41 number that they are interested in. There is no userspace consumer support for
42 this GTE instance in the HTE framework. 42 this GTE instance in the HTE framework.
43 43
44 The provider source code of both IRQ and GPIO 44 The provider source code of both IRQ and GPIO GTE instances is located at
45 ``drivers/hte/hte-tegra194.c``. The test drive 45 ``drivers/hte/hte-tegra194.c``. The test driver
46 ``drivers/hte/hte-tegra194-test.c`` demonstrat 46 ``drivers/hte/hte-tegra194-test.c`` demonstrates HTE API usage for both IRQ
47 and GPIO GTE. 47 and GPIO GTE.
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.