[PATCH] irq: add disable_irq_handler()/enable_irq_handler() functions

[Boris Brezillon]

Sometime we need to disable a specific handler on a shared irq line.
Currently, the only way this can be achieved is by freeing the irq handler
when we want to disable the irq and creating a new one when we want to
enable it.
This is not only adding some overhead to the disable/enable operations, but
the request_irq function cannot be called in atomic context, which means
it prevents disabling the interrupt in such situation.

This patch introduces three new functions: disable_irq_handler(),
disable_irq_handler_nosync() and enable_irq_handler() to allow disabling
a specific handler on a shared irq line.

Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx>
---
 include/linux/irqdesc.h |  1 +
 kernel/irq/manage.c     | 82 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 83 insertions(+)

diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
index fcea4e4..c8bd055 100644
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -52,6 +52,7 @@ struct irq_desc {
 	irq_preflow_handler_t	preflow_handler;
 #endif
 	struct irqaction	*action;	/* IRQ action list */
+	struct irqaction	*disabled_actions;	/* IRQ disabled action list */
 	unsigned int		status_use_accessors;
 	unsigned int		core_internal_state__do_not_mess_with_it;
 	unsigned int		depth;		/* nested irq disables */
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index f974485..4690ab4 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -458,6 +458,47 @@ void disable_irq_nosync(unsigned int irq)
 }
 EXPORT_SYMBOL(disable_irq_nosync);
 
+static int __disable_irq_handler_nosync(unsigned int irq, void *dev_id)
+{
+	unsigned long flags;
+	struct irqaction *action, **prev;
+	struct irq_desc *desc = irq_get_desc_buslock(irq, &flags, IRQ_GET_DESC_CHECK_GLOBAL);
+	int ret = 0;
+
+	if (!desc)
+		return -EINVAL;
+
+	for (action = desc->action, prev = &desc->action; action; action = action->next) {
+		if (action->dev_id == dev_id)
+			break;
+
+		prev = &action->next;
+	}
+
+	if (!action)
+		goto out;
+
+	*prev = action->next;
+
+	action->next = desc->disabled_actions;
+	desc->disabled_actions = action;
+	if (!desc->action) {
+		__disable_irq(desc, irq);
+		ret = 1;
+	}
+
+out:
+	irq_put_desc_busunlock(desc, flags);
+	return ret;
+}
+
+static void disable_irq_handler_nosync(unsigned int irq, void *dev_id)
+{
+	__disable_irq_handler_nosync(irq, dev_id);
+}
+EXPORT_SYMBOL(disable_irq_handler_nosync);
+
+
 /**
  *	disable_irq - disable an irq and wait for completion
  *	@irq: Interrupt to disable
@@ -477,6 +518,13 @@ void disable_irq(unsigned int irq)
 }
 EXPORT_SYMBOL(disable_irq);
 
+void disable_irq_handler(unsigned int irq, )
+{
+	if (__disable_irq_handler_nosync(irq) > 0)
+		synchronize_irq(irq);
+}
+EXPORT_SYMBOL(disable_irq);
+
 /**
  *	disable_hardirq - disables an irq and waits for hardirq completion
  *	@irq: Interrupt to disable
@@ -552,6 +600,40 @@ out:
 }
 EXPORT_SYMBOL(enable_irq);
 
+void enable_irq_handler(unsigned int irq, void *dev_id)
+{
+	unsigned long flags;
+	struct irqaction *action, **prev;
+	struct irq_desc *desc = irq_get_desc_buslock(irq, &flags, IRQ_GET_DESC_CHECK_GLOBAL);
+
+	if (!desc)
+		return -EINVAL;
+
+	for (action = desc->disabled_actions, prev = &desc->action; action;
+	     action = action->next) {
+		if (action->dev_id == dev_id)
+			break;
+
+		prev = &action->next;
+	}
+
+	if (!action)
+		goto out;
+
+	*prev = action->next;
+
+	action->next = desc->action;
+	desc->action = action;
+
+	if (!action->next)
+		__enable_irq(desc, irq);
+
+out:
+	irq_put_desc_busunlock(desc, flags);
+
+}
+EXPORT_SYMBOL(enable_irq_handler);
+
 static int set_irq_wake_real(unsigned int irq, unsigned int on)
 {
 	struct irq_desc *desc = irq_to_desc(irq);
-- 
1.9.1
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