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Commit ab9b32ee authored by Andi Kleen's avatar Andi Kleen Committed by Linus Torvalds
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[PATCH] x86_64: Better ATI timer fix 



The previous experiment for using apicmaintimer on ATI systems didn't
work out very well.  In particular laptops with C2/C3 support often
don't let it tick during idle, which makes it useless.  There were also
some other bugs that made the apicmaintimer often not used at all.

I tried some other experiments - running timer over RTC and some other
things but they didn't really work well neither.

I rechecked the specs now and it turns out this simple change is
actually enough to avoid the double ticks on the ATI systems.  We just
turn off IRQ 0 in the 8254 and only route it directly using the IO-APIC.

I tested it on a few ATI systems and it worked there.  In fact it worked
on all chipsets (NVidia, Intel, AMD, ATI) I tried it on.

According to the ACPI spec routing should always work through the
IO-APIC so I think it's the correct thing to do anyways (and most of the
old gunk in check_timer should be thrown away for x86-64).

But for 2.6.16 it's best to do a fairly minimal change:
 - Use the known to be working everywhere-but-ATI IRQ0 both over 8254
   and IO-APIC setup everywhere
 - Except on ATI disable IRQ0 in the 8254
 - Remove the code to select apicmaintimer on ATI chipsets
 - Add some boot options to allow to override this (just paranoia)

In 2.6.17 I hope to switch the default over to this for everybody.

Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent e8b91777

Documentation/x86_64/boot-options.txt

+4 −0
Original line number Diff line number Diff line
@@ -52,6 +52,10 @@ APICs 
		 apicmaintimer. Useful when your PIT timer is totally

		 broken.



   disable_8254_timer / enable_8254_timer

		 Enable interrupt 0 timer routing over the 8254 in addition to over

	         the IO-APIC. The kernel tries to set a sensible default.



Early Console



   syntax: earlyprintk=vga

arch/x86_64/kernel/io_apic.c

+29 −17
Original line number Diff line number Diff line
@@ -50,6 +50,8 @@ static int no_timer_check; 


int disable_timer_pin_1 __initdata;



int timer_over_8254 __initdata = 1;



/* Where if anywhere is the i8259 connect in external int mode */

static struct { int pin, apic; } ioapic_i8259 = { -1, -1 };
@@ -251,6 +253,20 @@ static int __init enable_ioapic_setup(char *str) 
__setup("noapic", disable_ioapic_setup);

__setup("apic", enable_ioapic_setup);



static int __init setup_disable_8254_timer(char *s)

{

	timer_over_8254 = -1;

	return 1;

}

static int __init setup_enable_8254_timer(char *s)

{

	timer_over_8254 = 2;

	return 1;

}



__setup("disable_8254_timer", setup_disable_8254_timer);

__setup("enable_8254_timer", setup_enable_8254_timer);



#include <asm/pci-direct.h>

#include <linux/pci_ids.h>

#include <linux/pci.h>
@@ -309,27 +325,20 @@ void __init check_ioapic(void) 
#endif

					/* RED-PEN skip them on mptables too? */

					return;



				/* This should be actually default, but

				   for 2.6.16 let's do it for ATI only where

				   it's really needed. */

				case PCI_VENDOR_ID_ATI:

					if (apic_runs_main_timer != 0)

						break;

#ifdef CONFIG_ACPI

					/* Don't do this for laptops right

					   right now because their timer

					   doesn't necessarily tick in C2/3 */

					if (acpi_fadt.revision >= 3 &&

			(acpi_fadt.plvl2_lat + acpi_fadt.plvl3_lat) < 1100) {

					if (timer_over_8254 == 1) {	

						timer_over_8254 = 0;	

					printk(KERN_INFO

"ATI board detected, but seems to be a laptop. Timer might be shakey, sorry\n");

						break;

		"ATI board detected. Disabling timer routing over 8254.\n");

					}	

#endif					

					printk(KERN_INFO

	     "ATI board detected. Using APIC/PM timer.\n");

					apic_runs_main_timer = 1;

					nohpet = 1;

					return;

				} 





				/* No multi-function device? */

				type = read_pci_config_byte(num,slot,func,

							    PCI_HEADER_TYPE);
@@ -1773,6 +1782,8 @@ static inline void unlock_ExtINT_logic(void) 
 * a wide range of boards and BIOS bugs.  Fortunately only the timer IRQ

 * is so screwy.  Thanks to Brian Perkins for testing/hacking this beast

 * fanatically on his truly buggy board.

 *

 * FIXME: really need to revamp this for modern platforms only.

 */

static inline void check_timer(void)

{
@@ -1795,6 +1806,7 @@ static inline void check_timer(void) 
	 */

	apic_write(APIC_LVT0, APIC_LVT_MASKED | APIC_DM_EXTINT);

	init_8259A(1);

	if (timer_over_8254 > 0)

		enable_8259A_irq(0);



	pin1  = find_isa_irq_pin(0, mp_INT);