[PATCH v3 2/2] docs: timers: hpet: Document userspace API and ioctl commands

["Habil Eren Türker" <habilerenturker@gmail.com>]

Add a dedicated 'Userspace API and ioctl Commands' section to clearly
document the supported ioctl interfaces extrapolated from
include/uapi/linux/hpet.h, including the layout of struct hpet_info.

Assisted-by: Google Gemini
Signed-off-by: Habil Eren Türker <habilerenturker@hotmail.com>
---
 Documentation/timers/hpet.rst | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/Documentation/timers/hpet.rst b/Documentation/timers/hpet.rst
index 8bb51d971..007e906ae 100644
--- a/Documentation/timers/hpet.rst
+++ b/Documentation/timers/hpet.rst
@@ -28,3 +28,32 @@ initialization.  An example of this initialization can be found in
 The driver provides a userspace API which resembles the API found in the
 RTC driver framework.  An example user space program is provided in
 ``samples/timers/hpet_example.c``
+
+Userspace API and ioctl Commands
+================================
+
+* ``HPET_IE_ON`` / ``HPET_IE_OFF``
+  Enables or disables the interrupt generation for the timer channel.
+
+* ``HPET_INFO``
+  It is used to query the capabilities and current status of the HPET. 
+  When the ioctl call is made, the kernel populates the ``struct hpet_info`` 
+  structure and returns it to userspace:
+
+  .. code-block:: c
+
+     struct hpet_info {
+         unsigned long hi_ireqfreq;	/* Hz */
+         unsigned long hi_flags;	/* information */
+         unsigned short hi_hpet;
+         unsigned short hi_timer;
+     };
+
+* ``HPET_EPI`` / ``HPET_DPI``
+  Enables or disables periodic interrupts. When activated, the timer 
+  triggers continuously at the specified frequency.
+
+* ``HPET_IRQFREQ``
+  Sets the interrupt frequency for the periodic timer. This request 
+  takes an unsigned long argument specifying the desired frequency in Hz.
+
-- 
2.47.3