[RFC PATCH 06/36] arm64: irq: introduce a helper for GIC priority initialization

[Vladimir Murzin]

From: Ada Couprie Diaz <ada.coupriediaz at arm.com>

Arm64's `init_IRQ()` calls `local_daif_restore()` to synchronize
interrupt masking via DAIF and switch to masking via PMR.  This
depends on a very specific behaviour of `local_daif_restore()` which
will clear DAIF if masking interrupts via PMR, which will get removed
in the future.

As `setup_arch()` cleared DA only earlier, introduce a dedicated
helper that explicitly initializes the PMR to mask interrupts and
clears DAIF, switching to IRQ priority masking.

Given it is a dedicated helper, add a lockdep assertion as
`setup_arch()` should always have called `trace_hardirqs_off()` when
clearing DA, otherwise something bad happened.

Signed-off-by: Ada Couprie Diaz <ada.coupriediaz at arm.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin at arm.com>
---
 arch/arm64/include/asm/daifflags.h | 15 +++++++++++++++
 arch/arm64/kernel/irq.c            |  7 +++----
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/daifflags.h b/arch/arm64/include/asm/daifflags.h
index 795b35128467..56341578e7e3 100644
--- a/arch/arm64/include/asm/daifflags.h
+++ b/arch/arm64/include/asm/daifflags.h
@@ -141,4 +141,19 @@ static __always_inline void local_daif_inherit(struct pt_regs *regs)
 	 */
 	write_sysreg(flags, daif);
 }
+
+/*
+ * During early boot, we unmask PSR.DA before the GIC has been set up.
+ * If we use IRQ priority masking, the PMR and PSR will be out of sync
+ * after the GIC is enabled : sync them up.
+ */
+static inline void local_interrupt_priority_init(void)
+{
+	WARN_ON(read_sysreg(daif) & PSR_A_BIT);
+	lockdep_assert_irqs_disabled();
+
+	gic_write_pmr(GIC_PRIO_IRQOFF);
+	write_sysreg(DAIF_PROCCTX, daif);
+}
+
 #endif
diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c
index 9fafd826002b..c73faa30268d 100644
--- a/arch/arm64/kernel/irq.c
+++ b/arch/arm64/kernel/irq.c
@@ -126,10 +126,9 @@ void __init init_IRQ(void)
 
 	if (system_uses_irq_prio_masking()) {
 		/*
-		 * Now that we have a stack for our IRQ handler, set
-		 * the PMR/PSR pair to a consistent state.
+		 * Now that we have a stack for our IRQ handler,
+		 * let's mask interrupts via the PMR.
 		 */
-		WARN_ON(read_sysreg(daif) & PSR_A_BIT);
-		local_daif_restore(DAIF_PROCCTX_NOIRQ);
+		local_interrupt_priority_init();
 	}
 }
-- 
2.34.1