linux-kernel - [PATCH] NTP: Let update_persistent

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Message-ID: <Pine.LNX.4.55.0805281856200.29522@cliff.in.clinika.pl>
Date:	Wed, 28 May 2008 19:15:41 +0100 (BST)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
cc:	Alessandro Zummo <a.zummo@...ertech.it>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] NTP: Let update_persistent_clock() sleep

 This is a change that makes the 11-minute RTC update be run in the
process context.  This is so that update_persistent_clock() can sleep,
which may be required for certain types of RTC hardware -- most notably
I2C devices.

Signed-off-by: Maciej W. Rozycki <macro@...ux-mips.org>
---
Hello,

 After the initial enthusiasm, I am not sure how my series of patches to
let read_persistent_clock() and update_persistent_clock() use the class
RTC subsystem is going to be handled.  As keeping the order of patches is 
required to avoid breakage in various places, I will try to coordinate the 
changes and submit them one by one as the dependencies get satisfied.  I 
hope this is OK and will take less than half a year. ;)

 Given this one applies to generic code and is required by all the other
changes, while not requiring anything and not meant to break anything, ;) 
I think this is ready to go.  It may be worth testing that moving the 
function into the process context does not cause any regressions for some 
obscure configuration.

 I am not sure who actually claims maintenance of kernel/time/ntp.c, but
it looks, Thomas, you seem to be our current time overseer -- could you
please speak out on this change?  I'd like this change to get applied
somewhere reasonable -- is it -mm?

  Maciej

patch-2.6.26-rc1-20080505-sync-cmos-work-0
diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/kernel/time/ntp.c linux-2.6.26-rc1-20080505/kernel/time/ntp.c
--- linux-2.6.26-rc1-20080505.macro/kernel/time/ntp.c	2008-05-05 02:56:03.000000000 +0000
+++ linux-2.6.26-rc1-20080505/kernel/time/ntp.c	2008-05-05 21:10:50.000000000 +0000
@@ -3,6 +3,8 @@
  *
  * NTP state machine interfaces and logic.
  *
+ * Copyright (c) 2008  Maciej W. Rozycki
+ *
  * This code was mainly moved from kernel/timer.c and kernel/time.c
  * Please see those files for relevant copyright info and historical
  * changelogs.
@@ -17,6 +19,7 @@
 #include <linux/capability.h>
 #include <linux/math64.h>
 #include <linux/clocksource.h>
+#include <linux/workqueue.h>
 #include <asm/timex.h>

 /*
@@ -218,11 +221,13 @@ void second_overflow(void)
 /* Disable the cmos update - used by virtualization and embedded */
 int no_sync_cmos_clock  __read_mostly;

-static void sync_cmos_clock(unsigned long dummy);
+static void sync_cmos_clock(unsigned long data);
+static void do_sync_cmos_clock(struct work_struct *work);

 static DEFINE_TIMER(sync_cmos_timer, sync_cmos_clock, 0, 0);
+static DECLARE_WORK(sync_cmos_work, do_sync_cmos_clock);

-static void sync_cmos_clock(unsigned long dummy)
+static void do_sync_cmos_clock(struct work_struct *work)
 {
 	struct timespec now, next;
 	int fail = 1;
@@ -261,6 +266,12 @@ static void sync_cmos_clock(unsigned lon
 	mod_timer(&sync_cmos_timer, jiffies + timespec_to_jiffies(&next));
 }

+static void sync_cmos_clock(unsigned long data)
+{
+	/* Some implementations of update_persistent_clock() may sleep.  */
+	schedule_work(&sync_cmos_work);
+}
+
 static void notify_cmos_timer(void)
 {
 	if (!no_sync_cmos_clock)
--
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