From 2ba7deef09dad6662dc4fa8b275af8d0794fd9fc Mon Sep 17 00:00:00 2001 From: Len Brown Date: Wed, 30 Jan 2008 13:31:02 +0100 Subject: [PATCH] x86: 32-bit IOAPIC: de-fang IRQ compression commit c434b7a6aedfe428ad17cd61b21b125a7b7a29ce (x86: avoid wasting IRQs for PCI devices) created a concept of "IRQ compression" on i386 to conserve IRQ numbers on systems with many sparsely populated IO APICs. The same scheme was also added to x86_64, but later removed when x86_64 recieved an IRQ over-haul that made it unnecessary -- including per-CPU IRQ vectors that greatly increased the IRQ capacity on the machine. i386 has not received the analogous over-haul, and thus a previous attempt to delete IRQ compression from i386 was rejected on the theory that there may exist machines that actually need it. The fact is that the author of IRQ compression patch was unable to confirm the actual existence of such a system. As a result, all i386 kernels with IOAPIC support pay the following: 1. confusion IRQ compression re-names the traditional IOAPIC pin numbers (aka ACPI GSI's) into sequential IRQ #s: ACPI: PCI Interrupt 0000:00:1c.0[A] -> GSI 20 (level, low) -> IRQ 16 ACPI: PCI Interrupt 0000:00:1c.1[B] -> GSI 21 (level, low) -> IRQ 17 ACPI: PCI Interrupt 0000:00:1c.2[C] -> GSI 22 (level, low) -> IRQ 18 ACPI: PCI Interrupt 0000:00:1c.3[D] -> GSI 23 (level, low) -> IRQ 19 ACPI: PCI Interrupt 0000:00:1c.4[A] -> GSI 20 (level, low) -> IRQ 16 This makes /proc/interrupts look different depending on system configuration and device probe order. It is also different than the x86_64 kernel running on the exact same system. As a result, programmers get confused when comparing systems. 2. complexity The IRQ code in Linux is already overly complex, and IRQ compression makes it worse. There have already been two bug workarounds related to IRQ compression -- the IRQ0 timer workaround and the VIA PCI IRQ workaround. 3. size All i386 kernels with IOAPIC support contain an int[4096] -- a 4 page array to contain the renamed IRQs. So while the irq compression code on i386 should really be deleted -- even before merging the x86_64 irq-overhaul, this patch simply disables it on all high volume systems to avoid problems #1 and #2 on most all i386 systems. A large system with pin numbers >=64 will still have compression to conserve limited IRQ numbers for sparse IOAPICS. However, the vast majority of the planet, those with only pin numbers < 64 will use an identity GSI -> IRQ mapping. Signed-off-by: Len Brown Signed-off-by: Ingo Molnar Signed-off-by: Thomas Gleixner Acked-by: "Eric W. Biederman" --- arch/x86/kernel/mpparse_32.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/mpparse_32.c b/arch/x86/kernel/mpparse_32.c index 22fc8d7dec11..bfcfc41f5607 100644 --- a/arch/x86/kernel/mpparse_32.c +++ b/arch/x86/kernel/mpparse_32.c @@ -1041,13 +1041,14 @@ void __init mp_config_acpi_legacy_irqs (void) } #define MAX_GSI_NUM 4096 +#define IRQ_COMPRESSION_START 64 int mp_register_gsi(u32 gsi, int triggering, int polarity) { int ioapic = -1; int ioapic_pin = 0; int idx, bit = 0; - static int pci_irq = 16; + static int pci_irq = IRQ_COMPRESSION_START; /* * Mapping between Global System Interrups, which * represent all possible interrupts, and IRQs @@ -1086,12 +1087,16 @@ int mp_register_gsi(u32 gsi, int triggering, int polarity) if ((1<= 64, use IRQ compression + */ + if ((gsi >= IRQ_COMPRESSION_START) + && (triggering == ACPI_LEVEL_SENSITIVE)) { /* * For PCI devices assign IRQs in order, avoiding gaps * due to unused I/O APIC pins.