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    Subject[RFC -tip] x86,apic -- reduce disable_apic usage
    Here is an attempt to bring more consistency for apic
    presence check. I hope I covered all the code flows.
    Though it's RFC. Please review and test if possible.

    -- Cyrill
    ---
    Instead of messing with (cpu_has_apic|disable_apic)
    to check if we have apic functional, better to distinguish
    them by logical kind. cpu_has_apic -- to check if we may
    use apic functionality, disable_apic -- to note that
    apic was disabled via command line.

    Other interesting (and a side one) issue I guess is that
    X86_FEATURE_APIC feature bit is always cleared if apic
    disabled via command line but not the reverse.

    Eventually this allow us to save a few lines of code.

    Also:

    1) No need to clear bit twice in APIC_init_uniprocessor.
    cpu_has_apic check for boot_cpu_data bit anyway.
    2) Don't check for disable_apic in print_all_ICs. It's
    already set. Always.
    3) Don't set disable_apic if there is no MPS support built in
    with acpi enabled. Even having SMP built kernel we're
    protected by acpi_lapic check in smp_sanity_check.
    At least we should be.

    Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
    ---
    arch/x86/kernel/apic/apic.c | 3 +--
    arch/x86/kernel/apic/io_apic.c | 6 +++---
    arch/x86/kernel/setup.c | 6 +-----
    3 files changed, 5 insertions(+), 10 deletions(-)

    Index: linux-2.6.git/arch/x86/kernel/apic/apic.c
    =====================================================================
    --- linux-2.6.git.orig/arch/x86/kernel/apic/apic.c
    +++ linux-2.6.git/arch/x86/kernel/apic/apic.c
    @@ -1173,7 +1173,7 @@ void __cpuinit setup_local_APIC(void)
    unsigned int value;
    int i, j;

    - if (disable_apic) {
    + if (!cpu_has_apic) {
    arch_disable_smp_support();
    return;
    }
    @@ -1651,7 +1651,6 @@ int __init APIC_init_uniprocessor(void)
    APIC_INTEGRATED(apic_version[boot_cpu_physical_apicid])) {
    pr_err("BIOS bug, local APIC 0x%x not detected!...\n",
    boot_cpu_physical_apicid);
    - clear_cpu_cap(&boot_cpu_data, X86_FEATURE_APIC);
    return -1;
    }
    #endif
    Index: linux-2.6.git/arch/x86/kernel/apic/io_apic.c
    =====================================================================
    --- linux-2.6.git.orig/arch/x86/kernel/apic/io_apic.c
    +++ linux-2.6.git/arch/x86/kernel/apic/io_apic.c
    @@ -1884,7 +1884,7 @@ __apicdebuginit(int) print_all_ICs(void)
    print_PIC();

    /* don't print out if apic is not there */
    - if (!cpu_has_apic || disable_apic)
    + if (!cpu_has_apic)
    return 0;

    print_all_local_APICs();
    @@ -3261,7 +3261,7 @@ static int msi_compose_msg(struct pci_de
    int err;
    unsigned dest;

    - if (disable_apic)
    + if (!cpu_has_apic)
    return -ENXIO;

    cfg = irq_cfg(irq);
    @@ -3714,7 +3714,7 @@ int arch_setup_ht_irq(unsigned int irq,
    struct irq_cfg *cfg;
    int err;

    - if (disable_apic)
    + if (!cpu_has_apic)
    return -ENXIO;

    cfg = irq_cfg(irq);
    Index: linux-2.6.git/arch/x86/kernel/setup.c
    =====================================================================
    --- linux-2.6.git.orig/arch/x86/kernel/setup.c
    +++ linux-2.6.git/arch/x86/kernel/setup.c
    @@ -795,12 +795,8 @@ void __init setup_arch(char **cmdline_p)
    /* after early param, so could get panic from serial */
    reserve_early_setup_data();

    - if (acpi_mps_check()) {
    -#ifdef CONFIG_X86_LOCAL_APIC
    - disable_apic = 1;
    -#endif
    + if (acpi_mps_check())
    setup_clear_cpu_cap(X86_FEATURE_APIC);
    - }

    #ifdef CONFIG_PCI
    if (pci_early_dump_regs)

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