LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
* [patch 2.6.25-rc5] kerneldoc for <linux/clk.h>
@ 2008-03-11  2:02 David Brownell
  2008-03-12 22:58 ` David Brownell
  0 siblings, 1 reply; 2+ messages in thread
From: David Brownell @ 2008-03-11  2:02 UTC (permalink / raw)
  To: Andrew Morton; +Cc: lkml, Russell King

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@users.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>

^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [patch 2.6.25-rc5] kerneldoc for <linux/clk.h>
  2008-03-11  2:02 [patch 2.6.25-rc5] kerneldoc for <linux/clk.h> David Brownell
@ 2008-03-12 22:58 ` David Brownell
  0 siblings, 0 replies; 2+ messages in thread
From: David Brownell @ 2008-03-12 22:58 UTC (permalink / raw)
  To: Andrew Morton; +Cc: lkml, Russell King

Proof-reading doesn't always cut it ... an editor could help!

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
---
Just editorial fixes to the $SUBJECT patch.

 Documentation/DocBook/kernel-api.tmpl |   13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

--- g26.orig/Documentation/DocBook/kernel-api.tmpl	2008-03-12 00:43:43.000000000 -0700
+++ g26/Documentation/DocBook/kernel-api.tmpl	2008-03-12 15:41:48.000000000 -0700
@@ -671,16 +671,15 @@ X!Idrivers/video/console/fonts.c
 	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.
+	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 <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.
+	mode</emphasis>.
+	This mode still incurs leakage currents, especially with finer
+	circuit geometries, but for CMOS circuits power is mostly used
+	by clocked state changes.
      </para>
 
      <para>

^ permalink raw reply	[flat|nested] 2+ messages in thread

end of thread, other threads:[~2008-03-12 23:03 UTC | newest]

Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2008-03-11  2:02 [patch 2.6.25-rc5] kerneldoc for <linux/clk.h> David Brownell
2008-03-12 22:58 ` David Brownell

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).