ARC: Support for high priority interrupts in the in-core intc

There is a bit of hack/kludge right now where we disable preemption if a
L2 (High prio) IRQ is taken while L1 (Low prio) is active.

Need to revisit this

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

1 files changed, 103 insertions, 1 deletions

diff --git a/arch/arc/kernel/irq.c b/arch/arc/kernel/irq.c
index 3c18e66386c7..ca70894e2309 100644
--- a/arch/arc/kernel/irq.c
+++ b/arch/arc/kernel/irq.c
@@ -23,15 +23,32 @@
  * what it does ?
  * -setup Vector Table Base Reg - in case Linux not linked at 0x8000_0000
  * -Disable all IRQs (on CPU side)
+ * -Optionally, setup the High priority Interrupts as Level 2 IRQs
  */
 void __init arc_init_IRQ(void)
 {
-	int level_mask = level_mask;
+	int level_mask = 0;
 
 	write_aux_reg(AUX_INTR_VEC_BASE, _int_vec_base_lds);
 
 	/* Disable all IRQs: enable them as devices request */
 	write_aux_reg(AUX_IENABLE, 0);
+
+       /* setup any high priority Interrupts (Level2 in ARCompact jargon) */
+#ifdef CONFIG_ARC_IRQ3_LV2
+	level_mask |= (1 << 3);
+#endif
+#ifdef CONFIG_ARC_IRQ5_LV2
+	level_mask |= (1 << 5);
+#endif
+#ifdef CONFIG_ARC_IRQ6_LV2
+	level_mask |= (1 << 6);
+#endif
+
+	if (level_mask) {
+		pr_info("Level-2 interrupts bitset %x\n", level_mask);
+		write_aux_reg(AUX_IRQ_LEV, level_mask);
+	}
 }
 
 /*
@@ -141,6 +158,90 @@ int __init get_hw_config_num_irq(void)
 	return 0;
 }
 
+/*
+ * arch_local_irq_enable - Enable interrupts.
+ *
+ * 1. Explicitly called to re-enable interrupts
+ * 2. Implicitly called from spin_unlock_irq, write_unlock_irq etc
+ *    which maybe in hard ISR itself
+ *
+ * Semantics of this function change depending on where it is called from:
+ *
+ * -If called from hard-ISR, it must not invert interrupt priorities
+ *  e.g. suppose TIMER is high priority (Level 2) IRQ
+ *    Time hard-ISR, timer_interrupt( ) calls spin_unlock_irq several times.
+ *    Here local_irq_enable( ) shd not re-enable lower priority interrupts
+ * -If called from soft-ISR, it must re-enable all interrupts
+ *    soft ISR are low prioity jobs which can be very slow, thus all IRQs
+ *    must be enabled while they run.
+ *    Now hardware context wise we may still be in L2 ISR (not done rtie)
+ *    still we must re-enable both L1 and L2 IRQs
+ *  Another twist is prev scenario with flow being
+ *     L1 ISR ==> interrupted by L2 ISR  ==> L2 soft ISR
+ *     here we must not re-enable Ll as prev Ll Interrupt's h/w context will get
+ *     over-written (this is deficiency in ARC700 Interrupt mechanism)
+ */
+
+#ifdef CONFIG_ARC_COMPACT_IRQ_LEVELS	/* Complex version for 2 IRQ levels */
+
+void arch_local_irq_enable(void)
+{
+
+	unsigned long flags;
+	flags = arch_local_save_flags();
+
+	/* Allow both L1 and L2 at the onset */
+	flags |= (STATUS_E1_MASK | STATUS_E2_MASK);
+
+	/* Called from hard ISR (between irq_enter and irq_exit) */
+	if (in_irq()) {
+
+		/* If in L2 ISR, don't re-enable any further IRQs as this can
+		 * cause IRQ priorities to get upside down. e.g. it could allow
+		 * L1 be taken while in L2 hard ISR which is wrong not only in
+		 * theory, it can also cause the dreaded L1-L2-L1 scenario
+		 */
+		if (flags & STATUS_A2_MASK)
+			flags &= ~(STATUS_E1_MASK | STATUS_E2_MASK);
+
+		/* Even if in L1 ISR, allowe Higher prio L2 IRQs */
+		else if (flags & STATUS_A1_MASK)
+			flags &= ~(STATUS_E1_MASK);
+	}
+
+	/* called from soft IRQ, ideally we want to re-enable all levels */
+
+	else if (in_softirq()) {
+
+		/* However if this is case of L1 interrupted by L2,
+		 * re-enabling both may cause whaco L1-L2-L1 scenario
+		 * because ARC700 allows level 1 to interrupt an active L2 ISR
+		 * Thus we disable both
+		 * However some code, executing in soft ISR wants some IRQs
+		 * to be enabled so we re-enable L2 only
+		 *
+		 * How do we determine L1 intr by L2
+		 *  -A2 is set (means in L2 ISR)
+		 *  -E1 is set in this ISR's pt_regs->status32 which is
+		 *      saved copy of status32_l2 when l2 ISR happened
+		 */
+		struct pt_regs *pt = get_irq_regs();
+		if ((flags & STATUS_A2_MASK) && pt &&
+		    (pt->status32 & STATUS_A1_MASK)) {
+			/*flags &= ~(STATUS_E1_MASK | STATUS_E2_MASK); */
+			flags &= ~(STATUS_E1_MASK);
+		}
+	}
+
+	arch_local_irq_restore(flags);
+}
+
+#else /* ! CONFIG_ARC_COMPACT_IRQ_LEVELS */
+
+/*
+ * Simpler version for only 1 level of interrupt
+ * Here we only Worry about Level 1 Bits
+ */
 void arch_local_irq_enable(void)
 {
 	unsigned long flags;
@@ -158,4 +259,5 @@ void arch_local_irq_enable(void)
 	flags |= (STATUS_E1_MASK | STATUS_E2_MASK);
 	arch_local_irq_restore(flags);
 }
+#endif
 EXPORT_SYMBOL(arch_local_irq_enable);