From e275ac477161a3df5c27e40c55f7af94cfb396cf Mon Sep 17 00:00:00 2001 From: David Brownell Date: Mon, 28 Apr 2008 02:11:56 -0700 Subject: [PATCH] kerneldoc for Add to the generated kerneldoc, with some overview to go along with those per-function descriptions. Signed-off-by: David Brownell Cc: Russell King Cc: Alessandro Zummo Cc: "Randy.Dunlap" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/DocBook/kernel-api.tmpl | 54 +++++++++++++++++++++++++++++++++++ 1 file changed, 54 insertions(+) diff --git a/Documentation/DocBook/kernel-api.tmpl b/Documentation/DocBook/kernel-api.tmpl index 488dd4a..617c2d9 100644 --- a/Documentation/DocBook/kernel-api.tmpl +++ b/Documentation/DocBook/kernel-api.tmpl @@ -645,4 +645,58 @@ X!Idrivers/video/console/fonts.c !Edrivers/i2c/i2c-core.c + + Clock Framework + + + The clock framework defines programming interfaces to support + software management of the system clock tree. + This framework is widely used with System-On-Chip (SOC) platforms + to support power management and various devices which may need + custom clock rates. + Note that these "clocks" don't relate to timekeeping or real + time clocks (RTCs), each of which have separate frameworks. + These struct clk instances may be used + to manage for example a 96 MHz signal that is used to shift bits + into and out of peripherals or busses, or otherwise trigger + synchronous state machine transitions in system hardware. + + + + Power management is supported by explicit software clock gating: + unused clocks are disabled, so the system doesn't waste power + changing the state of transistors that aren't in active use. + On some systems this may be backed by hardware clock gating, + where clocks are gated without being disabled in software. + Sections of chips that are powered but not clocked may be able + to retain their last state. + This low power state is often called a retention + mode. + This mode still incurs leakage currents, especially with finer + circuit geometries, but for CMOS circuits power is mostly used + by clocked state changes. + + + + Power-aware drivers only enable their clocks when the device + they manage is in active use. Also, system sleep states often + differ according to which clock domains are active: while a + "standby" state may allow wakeup from several active domains, a + "mem" (suspend-to-RAM) state may require a more wholesale shutdown + of clocks derived from higher speed PLLs and oscillators, limiting + the number of possible wakeup event sources. A driver's suspend + method may need to be aware of system-specific clock constraints + on the target sleep state. + + + + Some platforms support programmable clock generators. These + can be used by external chips of various kinds, such as other + CPUs, multimedia codecs, and devices with strict requirements + for interface clocking. + + +!Iinclude/linux/clk.h + + -- 2.7.4