From 2c3c1048746a4622d8c89a29670120dc8fab93c4 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 20:49:45 +0200 Subject: Adding upstream version 6.1.76. Signed-off-by: Daniel Baumann --- Documentation/timers/hpet.rst | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) create mode 100644 Documentation/timers/hpet.rst (limited to 'Documentation/timers/hpet.rst') diff --git a/Documentation/timers/hpet.rst b/Documentation/timers/hpet.rst new file mode 100644 index 000000000..c9d05d3ca --- /dev/null +++ b/Documentation/timers/hpet.rst @@ -0,0 +1,30 @@ +=========================================== +High Precision Event Timer Driver for Linux +=========================================== + +The High Precision Event Timer (HPET) hardware follows a specification +by Intel and Microsoft, revision 1. + +Each HPET has one fixed-rate counter (at 10+ MHz, hence "High Precision") +and up to 32 comparators. Normally three or more comparators are provided, +each of which can generate oneshot interrupts and at least one of which has +additional hardware to support periodic interrupts. The comparators are +also called "timers", which can be misleading since usually timers are +independent of each other ... these share a counter, complicating resets. + +HPET devices can support two interrupt routing modes. In one mode, the +comparators are additional interrupt sources with no particular system +role. Many x86 BIOS writers don't route HPET interrupts at all, which +prevents use of that mode. They support the other "legacy replacement" +mode where the first two comparators block interrupts from 8254 timers +and from the RTC. + +The driver supports detection of HPET driver allocation and initialization +of the HPET before the driver module_init routine is called. This enables +platform code which uses timer 0 or 1 as the main timer to intercept HPET +initialization. An example of this initialization can be found in +arch/x86/kernel/hpet.c. + +The driver provides a userspace API which resembles the API found in the +RTC driver framework. An example user space program is provided in +file:samples/timers/hpet_example.c -- cgit v1.2.3