linux-kernel - [tip:irq/urgent] genirq: Allow irq chips to mark themself oneshot safe

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Date:	Wed, 25 Jul 2012 03:53:04 -0700
From:	tip-bot for Thomas Gleixner <tglx@...utronix.de>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	torvalds@...ux-foundation.org, mtosatti@...hat.com,
	jan.kiszka@....de, tglx@...utronix.de, avi@...hat.com
Subject: [tip:irq/urgent] genirq:
  Allow irq chips to mark themself oneshot safe

Commit-ID:  dc9b229a58dc0dfed34272ff26c6d5fd17c674e0
Gitweb:     http://git.kernel.org/tip/dc9b229a58dc0dfed34272ff26c6d5fd17c674e0
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Fri, 13 Jul 2012 19:29:45 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Wed, 25 Jul 2012 12:46:38 +0200

genirq: Allow irq chips to mark themself oneshot safe

Some interrupt chips like MSI are oneshot safe by implementation. For
those interrupts we can avoid the mask/unmask sequence for threaded
interrupt handlers.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1207132056540.32033@ionos
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Avi Kivity <avi@...hat.com>
Cc: Marcelo Tosatti <mtosatti@...hat.com>
Cc: Jan Kiszka <jan.kiszka@....de>
---
 include/linux/irq.h |    1 +
 kernel/irq/manage.c |   15 ++++++++++++++-
 2 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/include/linux/irq.h b/include/linux/irq.h
index 553fb66..216b0ba 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -349,6 +349,7 @@ enum {
 	IRQCHIP_MASK_ON_SUSPEND		= (1 <<  2),
 	IRQCHIP_ONOFFLINE_ENABLED	= (1 <<  3),
 	IRQCHIP_SKIP_SET_WAKE		= (1 <<  4),
+	IRQCHIP_ONESHOT_SAFE		= (1 <<  5),
 };
 
 /* This include will go away once we isolated irq_desc usage to core code */
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 8c54823..2e326d1 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -960,6 +960,18 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
 	}
 
 	/*
+	 * Drivers are often written to work w/o knowledge about the
+	 * underlying irq chip implementation, so a request for a
+	 * threaded irq without a primary hard irq context handler
+	 * requires the ONESHOT flag to be set. Some irq chips like
+	 * MSI based interrupts are per se one shot safe. Check the
+	 * chip flags, so we can avoid the unmask dance at the end of
+	 * the threaded handler for those.
+	 */
+	if (desc->irq_data.chip->flags & IRQCHIP_ONESHOT_SAFE)
+		new->flags &= ~IRQF_ONESHOT;
+
+	/*
 	 * The following block of code has to be executed atomically
 	 */
 	raw_spin_lock_irqsave(&desc->lock, flags);
@@ -1033,7 +1045,8 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
 		 */
 		new->thread_mask = 1 << ffz(thread_mask);
 
-	} else if (new->handler == irq_default_primary_handler) {
+	} else if (new->handler == irq_default_primary_handler &&
+		   !(desc->irq_data.chip->flags & IRQCHIP_ONESHOT_SAFE)) {
 		/*
 		 * The interrupt was requested with handler = NULL, so
 		 * we use the default primary handler for it. But it
--
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