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Message-Id: <200803101902.54407.david-b@pacbell.net> Date: Mon, 10 Mar 2008 18:02:54 -0800 From: David Brownell <david-b@...bell.net> To: Andrew Morton <akpm@...ux-foundation.org> Cc: lkml <linux-kernel@...r.kernel.org>, Russell King <rmk@....linux.org.uk> Subject: [patch 2.6.25-rc5] kerneldoc for <linux/clk.h> Add <linux/clk.h> to the generated kerneldoc, with some overview to go along with those per-function descriptions. Signed-off-by: David Brownell <dbrownell@...rs.sourceforge.net> --- Documentation/DocBook/kernel-api.tmpl | 55 ++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) --- g26.orig/Documentation/DocBook/kernel-api.tmpl 2008-03-10 16:44:57.000000000 -0700 +++ g26/Documentation/DocBook/kernel-api.tmpl 2008-03-10 18:52:11.000000000 -0700 @@ -650,4 +650,59 @@ X!Idrivers/video/console/fonts.c !Edrivers/i2c/i2c-core.c </chapter> + <chapter id="clk"> + <title>Clock Framework</title> + + <para> + 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 <structname>struct clk</structname> 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. + </para> + + <para> + 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. + Circuits will still have leakage current to be managed, which + costs more with finer cicuit geometries, but for CMOS circuits + power is mostly spent by clocked state changes. + 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 <emphasis>retention + mode</emphasis>, in contrast to <emphasis>off</emphasis> where + power is cut and no state is retained but where leakage currents + may have a significant impact on battery life. + </para> + + <para> + 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. + </para> + + <para> + 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. + </para> + +!Iinclude/linux/clk.h + </chapter> + </book> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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