linux-kernel - RE: [PATCH] x86: apic

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Date:	Fri, 10 Oct 2008 09:11:06 -0700
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>, Ingo Molnar <mingo@...e.hu>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] x86: apic - unify APIC_DIVISOR



>-----Original Message-----
>From: Cyrill Gorcunov [mailto:gorcunov@...il.com]
>Sent: Friday, October 10, 2008 8:00 AM
>To: Ingo Molnar; Maciej W. Rozycki
>Cc: LKML; Pallipadi, Venkatesh
>Subject: [PATCH] x86: apic - unify APIC_DIVISOR
>
>Use APIC_DIVISOR being set to 16 for both 32/64bit
>mode. To escape APIC timer underflow during calibration
>set it to the maximum possible value.
>
>Also typo error (CONFG instead of proper CONFIG) fixed.
>The error was catched by Venkatesh Pallipadi, thanks a lot Venkatesh!
>See details on http://lkml.org/lkml/2008/10/9/425
>
>Reported-by: Venkatesh Pallipad <venkatesh.pallipadi@...el.com>
>Signed-off-by: Cyrill Gorcunov <gorcunov@...il.com>
>---
>
>Index: linux-2.6.git/arch/x86/kernel/apic.c
>===================================================================
>--- linux-2.6.git.orig/arch/x86/kernel/apic.c   2008-09-26
>20:43:47.000000000 +0400
>+++ linux-2.6.git/arch/x86/kernel/apic.c        2008-10-10
>16:37:26.000000000 +0400
>@@ -332,11 +332,7 @@ int lapic_get_maxlvt(void)
>  */
>
> /* Clock divisor */
>-#ifdef CONFG_X86_64
>-#define APIC_DIVISOR 1
>-#else
> #define APIC_DIVISOR 16
>-#endif
>
> /*
>  * This function sets up the local APIC timer, with a timeout of
>@@ -592,10 +588,10 @@ static int __init calibrate_APIC_clock(v
>        global_clock_event->event_handler = lapic_cal_handler;
>
>        /*
>-        * Setup the APIC counter to 1e9. There is no way the lapic
>+        * Setup the APIC counter to maximum. There is no way the lapic
>         * can underflow in the 100ms detection time frame
>         */
>-       __setup_APIC_LVTT(1000000000, 0, 0);
>+       __setup_APIC_LVTT(0xffffffff, 0, 0);
>
>        /* Let the interrupts run */
>        local_irq_enable();
>

Agree with the APIC_DIVISOR part.

But, not sure why/how the second change is related to this APIC_DIVISOR being 16.
Also, another nit. Technically we are not setting the "APIC counter to maximum"
as we do divide by 16 before programming initial count register in __setup_APIC_LVTT().

Thanks,
Venki
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