[PATCH 10/18] arm64: Introduce FIQ support

Hector Martin
2021-02-04T20:47:18Z

Apple SoCs (A11 and newer) have some interrupt sources hardwired to the
FIQ line. Implement support for this by simply treating IRQs and FIQs
the same way in the interrupt vectors. This is conditional on the
ARM64_NEEDS_FIQ CPU feature flag, and thus will not affect other
systems.

Root irqchip drivers can discriminate between IRQs and FIQs by checking
the ISR_EL1 system register.

Signed-off-by: Hector Martin <marcan@marcan.st>
---
arch/arm64/include/asm/assembler.h | 4 ++++
arch/arm64/include/asm/daifflags.h | 7 +++++++
arch/arm64/include/asm/irqflags.h | 17 +++++++++++++----
arch/arm64/kernel/entry.S | 27 +++++++++++++++++++++++----
4 files changed, 47 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index bf125c591116..6acfc372dc76 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -42,7 +42,11 @@

/* IRQ is the lowest priority flag, unconditionally unmask the rest. */
.macro enable_da_f
+alternative_if ARM64_NEEDS_FIQ
+ msr daifclr, #(8 | 4)
+alternative_else
msr daifclr, #(8 | 4 | 1)
+alternative_endif
.endm

/*
diff --git a/arch/arm64/include/asm/daifflags.h b/arch/arm64/include/asm/daifflags.h
index 1c26d7baa67f..228a6039c701 100644
--- a/arch/arm64/include/asm/daifflags.h
+++ b/arch/arm64/include/asm/daifflags.h
@@ -112,6 +112,13 @@ static inline void local_daif_restore(unsigned long flags)
* So we don't need additional synchronization here.
*/
gic_write_pmr(pmr);
+ } else if (system_uses_fiqs()) {
+ /*
+ * On systems that use FIQs, disable FIQs if IRQs are disabled.
+ * This can happen if the DAIF_* flags at the top of this file
+ * are used to set DAIF directly.
+ */
+ flags |= PSR_F_BIT;
}

write_sysreg(flags, daif);
diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
index ff328e5bbb75..689c573c4b47 100644
--- a/arch/arm64/include/asm/irqflags.h
+++ b/arch/arm64/include/asm/irqflags.h
@@ -19,8 +19,9 @@
* side effects for other flags. Keeping to this order makes it easier for
* entry.S to know which exceptions should be unmasked.
*
- * FIQ is never expected, but we mask it when we disable debug exceptions, and
- * unmask it at all other times.
+ * FIQ is never expected on most platforms, but we mask it when we disable
+ * debug exceptions, and unmask it at all other times. On platforms that
+ * require FIQs, it tracks IRQ masking.
*/

/*
@@ -34,8 +35,14 @@ static inline void arch_local_irq_enable(void)
WARN_ON_ONCE(pmr != GIC_PRIO_IRQON && pmr != GIC_PRIO_IRQOFF);
}

- asm volatile(ALTERNATIVE(
+ /*
+ * Yes, ALTERNATIVE() nests properly... only one of these should be
+ * active on any given platform.
+ */
+ asm volatile(ALTERNATIVE(ALTERNATIVE(
"msr daifclr, #2 // arch_local_irq_enable",
+ "msr daifclr, #3 // arch_local_irq_enable",
+ ARM64_NEEDS_FIQ),
__msr_s(SYS_ICC_PMR_EL1, "%0"),
ARM64_HAS_IRQ_PRIO_MASKING)
:
@@ -53,8 +60,10 @@ static inline void arch_local_irq_disable(void)
WARN_ON_ONCE(pmr != GIC_PRIO_IRQON && pmr != GIC_PRIO_IRQOFF);
}

- asm volatile(ALTERNATIVE(
+ asm volatile(ALTERNATIVE(ALTERNATIVE(
"msr daifset, #2 // arch_local_irq_disable",
+ "msr daifset, #3 // arch_local_irq_disable",
+ ARM64_NEEDS_FIQ),
__msr_s(SYS_ICC_PMR_EL1, "%0"),
ARM64_HAS_IRQ_PRIO_MASKING)
:
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index c9bae73f2621..81ca04ebe37b 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -60,7 +60,7 @@
#define BAD_FIQ 2
#define BAD_ERROR 3

- .macro kernel_ventry, el, label, regsize = 64
+ .macro kernel_ventry, el, label, regsize = 64, altlabel = 0, alt = 0
.align 7
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
.if \el == 0
@@ -87,7 +87,15 @@ alternative_else_nop_endif
tbnz x0, #THREAD_SHIFT, 0f
sub x0, sp, x0 // x0'' = sp' - x0' = (sp + x0) - sp = x0
sub sp, sp, x0 // sp'' = sp' - x0 = (sp + x0) - x0 = sp
+ .if \altlabel != 0
+ alternative_if \alt
+ b el\()\el\()_\altlabel
+ alternative_else
b el\()\el\()_\label
+ alternative_endif
+ .else
+ b el\()\el\()_\label
+ .endif

0:
/*
@@ -119,7 +127,15 @@ alternative_else_nop_endif
sub sp, sp, x0
mrs x0, tpidrro_el0
#endif
+ .if \altlabel != 0
+ alternative_if \alt
+ b el\()\el\()_\altlabel
+ alternative_else
b el\()\el\()_\label
+ alternative_endif
+ .else
+ b el\()\el\()_\label
+ .endif
.endm

.macro tramp_alias, dst, sym
@@ -547,18 +563,21 @@ SYM_CODE_START(vectors)

kernel_ventry 1, sync // Synchronous EL1h
kernel_ventry 1, irq // IRQ EL1h
- kernel_ventry 1, fiq_invalid // FIQ EL1h
+ // FIQ EL1h
+ kernel_ventry 1, fiq_invalid, 64, irq, ARM64_NEEDS_FIQ
kernel_ventry 1, error // Error EL1h

kernel_ventry 0, sync // Synchronous 64-bit EL0
kernel_ventry 0, irq // IRQ 64-bit EL0
- kernel_ventry 0, fiq_invalid // FIQ 64-bit EL0
+ // FIQ 64-bit EL0
+ kernel_ventry 0, fiq_invalid, 64, irq, ARM64_NEEDS_FIQ
kernel_ventry 0, error // Error 64-bit EL0

#ifdef CONFIG_COMPAT
kernel_ventry 0, sync_compat, 32 // Synchronous 32-bit EL0
kernel_ventry 0, irq_compat, 32 // IRQ 32-bit EL0
- kernel_ventry 0, fiq_invalid_compat, 32 // FIQ 32-bit EL0
+ // FIQ 32-bit EL0
+ kernel_ventry 0, fiq_invalid_compat, 32, irq_compat, ARM64_NEEDS_FIQ
kernel_ventry 0, error_compat, 32 // Error 32-bit EL0
#else
kernel_ventry 0, sync_invalid, 32 // Synchronous 32-bit EL0
--
2.30.0