irqchip/gic-v3: Fix priority comparison when non-secure priorities are used

When non-secure priorities are used, compared to the raw priority set,
the value read back from RPR is also right-shifted by one and the
highest bit set.

Add a macro to do the modifications to the raw priority when doing the
comparison against the RPR value. This corrects the pseudo-NMI behavior
when non-secure priorities in the GIC are used. Tested on 5.10 with
the "IPI as pseudo-NMI" series [1] applied on MT8195.

[1] https://lore.kernel.org/linux-arm-kernel/1604317487-14543-1-git-send-email-sumit.garg@linaro.org/

Fixes: 33678059 ("irqchip/gic-v3: Support pseudo-NMIs when SCR_EL3.FIQ == 0")
Reviewed-by: NAlexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: NChen-Yu Tsai <wenst@chromium.org>
[maz: Added comment contributed by Alex]
Signed-off-by: NMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210811171505.1502090-1-wenst@chromium.org

drivers/irqchip/irq-gic-v3.c

@@ -100,6 +100,27 @@ EXPORT_SYMBOL(gic_pmr_sync);
 DEFINE_STATIC_KEY_FALSE(gic_nonsecure_priorities);
 EXPORT_SYMBOL(gic_nonsecure_priorities);
 
+/*
+ * When the Non-secure world has access to group 0 interrupts (as a
+ * consequence of SCR_EL3.FIQ == 0), reading the ICC_RPR_EL1 register will
+ * return the Distributor's view of the interrupt priority.
+ *
+ * When GIC security is enabled (GICD_CTLR.DS == 0), the interrupt priority
+ * written by software is moved to the Non-secure range by the Distributor.
+ *
+ * If both are true (which is when gic_nonsecure_priorities gets enabled),
+ * we need to shift down the priority programmed by software to match it
+ * against the value returned by ICC_RPR_EL1.
+ */
+#define GICD_INT_RPR_PRI(priority)					\
+	({								\
+		u32 __priority = (priority);				\
+		if (static_branch_unlikely(&gic_nonsecure_priorities))	\
+			__priority = 0x80 | (__priority >> 1);		\
+									\
+		__priority;						\
+	})
+
 /* ppi_nmi_refs[n] == number of cpus having ppi[n + 16] set as NMI */
 static refcount_t *ppi_nmi_refs;
 
@@ -687,7 +708,7 @@ static asmlinkage void __exception_irq_entry gic_handle_irq(struct pt_regs *regs
 		return;
 
 	if (gic_supports_nmi() &&
-	    unlikely(gic_read_rpr() == GICD_INT_NMI_PRI)) {
+	    unlikely(gic_read_rpr() == GICD_INT_RPR_PRI(GICD_INT_NMI_PRI))) {
 		gic_handle_nmi(irqnr, regs);
 		return;
 	}