FROMLIST: genirq: Allow an interrupt to be marked as 'raw'

Some interrupts (such as the rescheduling IPI) rely on not going through
the irq_enter()/irq_exit() calls. To distinguish such interrupts, add
a new IRQ flag that allows the low-level handling code to sidestep the
enter()/exit() calls.

Only the architecture code is expected to use this. It will do the wrong
thing on normal interrupts. Note that this is a band-aid until we can
move to some more correct infrastructure (such as kernel/entry/common.c).

Bug: 191808738
Link: https://lore.kernel.org/lkml/20201124141449.572446-3-maz@kernel.org/
Change-Id: I0609a8b689219ba9e769c8b9f7fcf1e77a0ff1ca
Signed-off-by: Marc Zyngier <maz@kernel.org>
[minor port to 5.10]
Signed-off-by: Stephen Dickey <dickey@codeaurora.org>

include/linux/irq.h

@@ -72,6 +72,7 @@ enum irqchip_irq_state;
  *				  mechanism and from core side polling.
  * IRQ_DISABLE_UNLAZY		- Disable lazy irq disable
  * IRQ_HIDDEN			- Don't show up in /proc/interrupts
+ * IRQ_RAW			- Skip tick management and irqtime accounting
  */
 enum {
 	IRQ_TYPE_NONE		= 0x00000000,
@@ -99,6 +100,7 @@ enum {
 	IRQ_IS_POLLED		= (1 << 18),
 	IRQ_DISABLE_UNLAZY	= (1 << 19),
 	IRQ_HIDDEN		= (1 << 20),
+	IRQ_RAW			= (1 << 21),
 };
 
 #define IRQF_MODIFY_MASK	\

kernel/irq/Kconfig

@@ -109,6 +109,9 @@ config GENERIC_IRQ_MATRIX_ALLOCATOR
 config GENERIC_IRQ_RESERVATION_MODE
 	bool
 
+config ARCH_WANTS_IRQ_RAW
+	bool
+
 # Support forced irq threading
 config IRQ_FORCED_THREADING
        bool

kernel/irq/debugfs.c

@@ -140,6 +140,7 @@ static const struct irq_bit_descr irqdesc_states[] = {
 	BIT_MASK_DESCR(_IRQ_IS_POLLED),
 	BIT_MASK_DESCR(_IRQ_DISABLE_UNLAZY),
 	BIT_MASK_DESCR(_IRQ_HIDDEN),
+	BIT_MASK_DESCR(_IRQ_RAW),
 };
 
 static const struct irq_bit_descr irqdesc_istates[] = {

kernel/irq/irqdesc.c

@@ -667,10 +667,9 @@ int __handle_domain_irq(struct irq_domain *domain, unsigned int hwirq,
 {
 	struct pt_regs *old_regs = set_irq_regs(regs);
 	unsigned int irq = hwirq;
+	struct irq_desc *desc;
 	int ret = 0;
 
-	irq_enter();
-
 #ifdef CONFIG_IRQ_DOMAIN
 	if (lookup)
 		irq = irq_find_mapping(domain, hwirq);
@@ -680,14 +679,22 @@ int __handle_domain_irq(struct irq_domain *domain, unsigned int hwirq,
 	 * Some hardware gives randomly wrong interrupts.  Rather
 	 * than crashing, do something sensible.
 	 */
-	if (unlikely(!irq || irq >= nr_irqs)) {
+	if (unlikely(!irq || irq >= nr_irqs || !(desc = irq_to_desc(irq)))) {
 		ack_bad_irq(irq);
 		ret = -EINVAL;
-	} else {
-		generic_handle_irq(irq);
+		goto out;
 	}
 
-	irq_exit();
+	if (IS_ENABLED(CONFIG_ARCH_WANTS_IRQ_RAW) &&
+	    unlikely(irq_settings_is_raw(desc))) {
+		generic_handle_irq_desc(desc);
+	} else {
+		irq_enter();
+		generic_handle_irq_desc(desc);
+		irq_exit();
+	}
+
+out:
 	set_irq_regs(old_regs);
 	return ret;
 }

kernel/irq/settings.h

@@ -18,6 +18,7 @@ enum {
 	_IRQ_IS_POLLED		= IRQ_IS_POLLED,
 	_IRQ_DISABLE_UNLAZY	= IRQ_DISABLE_UNLAZY,
 	_IRQ_HIDDEN		= IRQ_HIDDEN,
+	_IRQ_RAW		= IRQ_RAW,
 	_IRQF_MODIFY_MASK	= IRQF_MODIFY_MASK,
 };
 
@@ -33,6 +34,7 @@ enum {
 #define IRQ_IS_POLLED		GOT_YOU_MORON
 #define IRQ_DISABLE_UNLAZY	GOT_YOU_MORON
 #define IRQ_HIDDEN		GOT_YOU_MORON
+#define IRQ_RAW			GOT_YOU_MORON
 #undef IRQF_MODIFY_MASK
 #define IRQF_MODIFY_MASK	GOT_YOU_MORON
 
@@ -180,3 +182,16 @@ static inline bool irq_settings_is_hidden(struct irq_desc *desc)
 {
 	return desc->status_use_accessors & _IRQ_HIDDEN;
 }
+
+static inline bool irq_settings_is_raw(struct irq_desc *desc)
+{
+	if (IS_ENABLED(CONFIG_ARCH_WANTS_IRQ_RAW))
+		return desc->status_use_accessors & _IRQ_RAW;
+
+	/*
+	 * Using IRQ_RAW on architectures that don't expect it is
+	 * likely to be wrong.
+	 */
+	WARN_ON_ONCE(1);
+	return false;
+}