linux-kernel - [PATCH] let setup_irq reenable a shared irq

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Date:	Mon, 28 Apr 2008 13:12:51 +0200
From:	Uwe Kleine-König <Uwe.Kleine-Koenig@...i.com>
To:	<linux-kernel@...r.kernel.org>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] let setup_irq reenable a shared irq

Consider two devices A and B sharing an irq and B already asserts the irq on
a booting machine.
If the driver for A is loaded first the irq starts triggering and gets
disabled after some time by note_interrupt().  Later when the driver for B
is loaded the interrupt should be reenabled---other wise both A and B don't
work properly.

Signed-off-by: Uwe Kleine-König <Uwe.Kleine-Koenig@...i.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/irq/manage.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 438a014..831ebb2 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -365,11 +365,18 @@ int setup_irq(unsigned int irq, struct irqaction *new)
 
 		desc->status &= ~(IRQ_AUTODETECT | IRQ_WAITING |
 				  IRQ_INPROGRESS);
+	}
+
+	/* in the shared case the interrupt might be disabled if a device
+	 * asserts the irq but the corresponding driver wasn't the first to be
+	 * loaded.  So retry enabling the irq.
+	 */
+	if (!shared || desc->status & IRQ_DISABLED) {
 
 		if (!(desc->status & IRQ_NOAUTOEN)) {
 			desc->depth = 0;
 			desc->status &= ~IRQ_DISABLED;
-			if (desc->chip->startup)
+			if (!shared && desc->chip->startup)
 				desc->chip->startup(irq);
 			else
 				desc->chip->enable(irq);
-- 
1.5.5.1

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