Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 47 insertions, 0 deletions

diff --git a/Documentation/driver-api/hte/tegra-hte.rst b/Documentation/driver-api/hte/tegra-hte.rst
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+.. 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.