Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=6b3964cde70cfe6db79d35b42137431ef7d2f7e4
Commit:     6b3964cde70cfe6db79d35b42137431ef7d2f7e4
Parent:     8559840c4ca3f2fff73a882803bc8916078fac1f
Author:     Thomas Gleixner <[EMAIL PROTECTED]>
AuthorDate: Thu Mar 22 22:46:18 2007 +0100
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Thu Mar 22 19:33:30 2007 -0700

    [PATCH] i386: clockevents fix breakage on Geode/Cyrix PIT implementations
    
    The PIT has no dedicated mode for shut down. The only way to disable PIT
    is to put it into one shot mode. AMD implementations of PIT on Geode
    (also observed on Cyrix) are confused by an "empty" transition from
    CLOCK_EVT_MODE_UNUSED to CLOCK_EVT_MODE_SHUTDOWN, which puts the PIT
    into one shot mode momentarily.
    
    I realized after staring helpless at the bug report
    http://bugzilla.kernel.org/show_bug.cgi?id=8027 for quite a while, that
    the only change, which might influence the bogomips calibration, is the
    above transition during the PIT initialization.
    
    Avoiding the unnecessary switch to oneshot and later to periodic mode
    fixes the weird bogomips value and also the resulting slowness.
    
    The fix is confirmed on OLPC and another Geode based box.
    
    Note: this is unrelated to the Dual Core problem discussed here:
    http://lkml.org/lkml/2007/3/17/48
    
    Signed-off-by: Thomas Gleixner <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
 arch/i386/kernel/i8253.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/arch/i386/kernel/i8253.c b/arch/i386/kernel/i8253.c
index 5cbb776..10cef5c 100644
--- a/arch/i386/kernel/i8253.c
+++ b/arch/i386/kernel/i8253.c
@@ -47,9 +47,17 @@ static void init_pit_timer(enum clock_event_mode mode,
                outb(LATCH >> 8 , PIT_CH0);     /* MSB */
                break;
 
-       case CLOCK_EVT_MODE_ONESHOT:
+       /*
+        * Avoid unnecessary state transitions, as it confuses
+        * Geode / Cyrix based boxen.
+        */
        case CLOCK_EVT_MODE_SHUTDOWN:
+               if (evt->mode == CLOCK_EVT_MODE_UNUSED)
+                       break;
        case CLOCK_EVT_MODE_UNUSED:
+               if (evt->mode == CLOCK_EVT_MODE_SHUTDOWN)
+                       break;
+       case CLOCK_EVT_MODE_ONESHOT:
                /* One shot setup */
                outb_p(0x38, PIT_MODE);
                udelay(10);
-
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