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

Hector Martin
2021-02-15T12:20:17Z

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