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    Subject[PATCH v2 07/25] arm64: cpufeature: Add a feature for FIQ support
    Date
    Apple ARM SoCs (A11 and newer) have some interrupt sources hard-wired to
    the FIQ line. Introduce a cpufeature that can be used to enable FIQ
    handling via alternatives.

    This is currently enabled for all Apple CPUs. If/when support is
    implemented for older (pre-A11) iPhone/iPad SoCs which do not need FIQs,
    or if newer SoCs are released without the FIQ requirement, we can
    revisit the condition.

    Signed-off-by: Hector Martin <marcan@marcan.st>
    ---
    arch/arm64/Kconfig | 11 +++++++++++
    arch/arm64/include/asm/cpucaps.h | 3 ++-
    arch/arm64/kernel/cpufeature.c | 14 ++++++++++++++
    3 files changed, 27 insertions(+), 1 deletion(-)

    diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
    index f39568b28ec1..fbc02af404b6 100644
    --- a/arch/arm64/Kconfig
    +++ b/arch/arm64/Kconfig
    @@ -1756,6 +1756,17 @@ config ARM64_DEBUG_PRIORITY_MASKING
    If unsure, say N
    endif

    +config ARM64_FIQ_SUPPORT
    + bool "Support for FIQ interrupts"
    + help
    + Adds support for handling FIQ interrupts as normal IRQs.
    + This is required on Apple platforms where some IRQ sources are
    + hardwired to the FIQ interrupt line.
    +
    + This option only affects platforms that require FIQ handling.
    + On all other platforms, unexpected FIQs will continue to
    + trigger a kernel panic.
    +
    config RELOCATABLE
    bool "Build a relocatable kernel image" if EXPERT
    select ARCH_HAS_RELR
    diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
    index b77d997b173b..c36d926ad801 100644
    --- a/arch/arm64/include/asm/cpucaps.h
    +++ b/arch/arm64/include/asm/cpucaps.h
    @@ -66,7 +66,8 @@
    #define ARM64_WORKAROUND_1508412 58
    #define ARM64_HAS_LDAPR 59
    #define ARM64_KVM_PROTECTED_MODE 60
    +#define ARM64_NEEDS_FIQ 61

    -#define ARM64_NCAPS 61
    +#define ARM64_NCAPS 62

    #endif /* __ASM_CPUCAPS_H */
    diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
    index e99eddec0a46..9fde84beabf1 100644
    --- a/arch/arm64/kernel/cpufeature.c
    +++ b/arch/arm64/kernel/cpufeature.c
    @@ -1237,6 +1237,12 @@ static bool has_cache_idc(const struct arm64_cpu_capabilities *entry,
    return ctr & BIT(CTR_IDC_SHIFT);
    }

    +static bool needs_fiq(const struct arm64_cpu_capabilities *entry, int __unused)
    +{
    + /* All supported Apple cores need this */
    + return read_cpuid_implementor() == ARM_CPU_IMP_APPLE;
    +}
    +
    static void cpu_emulate_effective_ctr(const struct arm64_cpu_capabilities *__unused)
    {
    /*
    @@ -2154,6 +2160,14 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
    .matches = has_cpuid_feature,
    .min_field_value = 1,
    },
    +#ifdef CONFIG_ARM64_FIQ_SUPPORT
    + {
    + .desc = "FIQs",
    + .capability = ARM64_NEEDS_FIQ,
    + .type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
    + .matches = needs_fiq,
    + },
    +#endif
    {},
    };

    --
    2.30.0
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