+
+ /* a BPR of 0 means the group priority bits are [7:1];
+ * a BPR of 1 means they are [7:2], and so on down to
+ * a BPR of 7 meaning no group priority bits at all.
+ */
+ mask = ~0U << ((bpr & 7) + 1);
+
+ return GIC_GET_PRIORITY(irq, cpu) & mask;
+}
+
+static void gic_activate_irq(GICState *s, int cpu, int irq)
+{
+ /* Set the appropriate Active Priority Register bit for this IRQ,
+ * and update the running priority.
+ */
+ int prio = gic_get_group_priority(s, cpu, irq);
+ int preemption_level = prio >> (GIC_MIN_BPR + 1);
+ int regno = preemption_level / 32;
+ int bitno = preemption_level % 32;
+
+ if (gic_has_groups(s) && GIC_TEST_GROUP(irq, (1 << cpu))) {
+ s->nsapr[regno][cpu] |= (1 << bitno);
+ } else {
+ s->apr[regno][cpu] |= (1 << bitno);
+ }
+
+ s->running_priority[cpu] = prio;
+ GIC_SET_ACTIVE(irq, 1 << cpu);
+}
+
+static int gic_get_prio_from_apr_bits(GICState *s, int cpu)
+{
+ /* Recalculate the current running priority for this CPU based
+ * on the set bits in the Active Priority Registers.
+ */
+ int i;
+ for (i = 0; i < GIC_NR_APRS; i++) {
+ uint32_t apr = s->apr[i][cpu] | s->nsapr[i][cpu];
+ if (!apr) {
+ continue;
+ }
+ return (i * 32 + ctz32(apr)) << (GIC_MIN_BPR + 1);
+ }
+ return 0x100;
+}
+
+static void gic_drop_prio(GICState *s, int cpu, int group)
+{
+ /* Drop the priority of the currently active interrupt in the
+ * specified group.
+ *
+ * Note that we can guarantee (because of the requirement to nest
+ * GICC_IAR reads [which activate an interrupt and raise priority]
+ * with GICC_EOIR writes [which drop the priority for the interrupt])
+ * that the interrupt we're being called for is the highest priority
+ * active interrupt, meaning that it has the lowest set bit in the
+ * APR registers.
+ *
+ * If the guest does not honour the ordering constraints then the
+ * behaviour of the GIC is UNPREDICTABLE, which for us means that
+ * the values of the APR registers might become incorrect and the
+ * running priority will be wrong, so interrupts that should preempt
+ * might not do so, and interrupts that should not preempt might do so.
+ */
+ int i;
+
+ for (i = 0; i < GIC_NR_APRS; i++) {
+ uint32_t *papr = group ? &s->nsapr[i][cpu] : &s->apr[i][cpu];
+ if (!*papr) {
+ continue;
+ }
+ /* Clear lowest set bit */
+ *papr &= *papr - 1;
+ break;
+ }
+
+ s->running_priority[cpu] = gic_get_prio_from_apr_bits(s, cpu);