From d11d5794e0c21a1054e6cd57381050a999ad7232 Mon Sep 17 00:00:00 2001 From: "Maciej W. Rozycki" Date: Wed, 21 May 2008 22:09:11 +0100 Subject: [PATCH] x86: I/O APIC: AEOI timer acknowledgement clean-ups The code that used to be in do_slow_gettimeoffset() that relied on the IRR bit of the master 8259A PIC for IRQ0 to check the state of the output timer 0 of the PIT is no longer there. As a result, there is no need to use the POLL command to acknowledge the timer interrupt in the "8259A Virtual Wire", except for the NMI watchdog when the i82489DX APIC is used (this is because this particular APIC treats NMIs as level-triggered and keeping the input asserted would keep motherboard NMI sources held off for too long). Remove the unneeded bits and adjust comments accordingly. Signed-off-by: Maciej W. Rozycki Signed-off-by: Ingo Molnar --- arch/x86/kernel/io_apic_32.c | 20 +++++++++----------- arch/x86/kernel/io_apic_64.c | 7 ++----- arch/x86/kernel/nmi_32.c | 2 +- arch/x86/kernel/time_32.c | 3 +-- 4 files changed, 13 insertions(+), 19 deletions(-) diff --git a/arch/x86/kernel/io_apic_32.c b/arch/x86/kernel/io_apic_32.c index a40d54fc1f..c64b3f5cc1 100644 --- a/arch/x86/kernel/io_apic_32.c +++ b/arch/x86/kernel/io_apic_32.c @@ -2146,19 +2146,17 @@ static inline void __init check_timer(void) set_intr_gate(vector, interrupt[0]); /* - * Subtle, code in do_timer_interrupt() expects an AEOI - * mode for the 8259A whenever interrupts are routed - * through I/O APICs. Also IRQ0 has to be enabled in - * the 8259A which implies the virtual wire has to be - * disabled in the local APIC. Finally timer interrupts - * need to be acknowledged manually in the 8259A for - * timer_interrupt() and for the i82489DX when using - * the NMI watchdog. + * As IRQ0 is to be enabled in the 8259A, the virtual + * wire has to be disabled in the local APIC. Also + * timer interrupts need to be acknowledged manually in + * the 8259A for the i82489DX when using the NMI + * watchdog as that APIC treats NMIs as level-triggered. + * The AEOI mode will finish them in the 8259A + * automatically. */ apic_write_around(APIC_LVT0, APIC_LVT_MASKED | APIC_DM_EXTINT); init_8259A(1); - timer_ack = !cpu_has_tsc; - timer_ack |= (nmi_watchdog == NMI_IO_APIC && !APIC_INTEGRATED(ver)); + timer_ack = (nmi_watchdog == NMI_IO_APIC && !APIC_INTEGRATED(ver)); if (timer_over_8254 > 0) enable_8259A_irq(0); @@ -2219,6 +2217,7 @@ static inline void __init check_timer(void) printk(KERN_WARNING "timer doesn't work through the IO-APIC - disabling NMI Watchdog!\n"); nmi_watchdog = 0; } + timer_ack = 0; printk(KERN_INFO "...trying to set up timer as Virtual Wire IRQ..."); @@ -2237,7 +2236,6 @@ static inline void __init check_timer(void) printk(KERN_INFO "...trying to set up timer as ExtINT IRQ..."); - timer_ack = 0; init_8259A(0); make_8259A_irq(0); apic_write_around(APIC_LVT0, APIC_DM_EXTINT); diff --git a/arch/x86/kernel/io_apic_64.c b/arch/x86/kernel/io_apic_64.c index ef1a8dfcc5..7c34e38e42 100644 --- a/arch/x86/kernel/io_apic_64.c +++ b/arch/x86/kernel/io_apic_64.c @@ -1669,11 +1669,8 @@ static inline void __init check_timer(void) assign_irq_vector(0, TARGET_CPUS); /* - * Subtle, code in do_timer_interrupt() expects an AEOI - * mode for the 8259A whenever interrupts are routed - * through I/O APICs. Also IRQ0 has to be enabled in - * the 8259A which implies the virtual wire has to be - * disabled in the local APIC. + * As IRQ0 is to be enabled in the 8259A, the virtual + * wire has to be disabled in the local APIC. */ apic_write(APIC_LVT0, APIC_LVT_MASKED | APIC_DM_EXTINT); init_8259A(1); diff --git a/arch/x86/kernel/nmi_32.c b/arch/x86/kernel/nmi_32.c index 11b14bbaa6..d322901c38 100644 --- a/arch/x86/kernel/nmi_32.c +++ b/arch/x86/kernel/nmi_32.c @@ -131,7 +131,7 @@ int __init check_nmi_watchdog(void) kfree(prev_nmi_count); return 0; error: - timer_ack = !cpu_has_tsc; + timer_ack = 0; return -1; } diff --git a/arch/x86/kernel/time_32.c b/arch/x86/kernel/time_32.c index 2ff21f3989..5f29f12da5 100644 --- a/arch/x86/kernel/time_32.c +++ b/arch/x86/kernel/time_32.c @@ -84,8 +84,7 @@ irqreturn_t timer_interrupt(int irq, void *dev_id) if (timer_ack) { /* * Subtle, when I/O APICs are used we have to ack timer IRQ - * manually to reset the IRR bit for do_slow_gettimeoffset(). - * This will also deassert NMI lines for the watchdog if run + * manually to deassert NMI lines for the watchdog if run * on an 82489DX-based system. */ spin_lock(&i8259A_lock); -- 2.39.5