[PATCH v2 07/25] arm64: cpufeature: Add a feature for FIQ support

[Hector Martin]

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 <mar...@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