[PATCH 1/6] ARM: gic: use handle_fasteoi_irq for SPIs

[will.deacon@arm.com (Will Deacon)]

Currently, the gic uses handle_level_irq for handling SPIs (Shared
Peripheral Interrupts), requiring active interrupts to be masked at
the distributor level during IRQ handling.

On a virtualised system, only the CPU interfaces are virtualised in
hardware. Accesses to the distributor must be trapped by the
hypervisor, adding latency to the critical interrupt path in Linux.

This patch modifies the GIC code to use handle_fasteoi_irq for handling
interrupts, which only requires us to signal EOI to the CPU interface
when handling is complete. Cascaded IRQ handling is also updated so
that EOI is signalled after handling.

Note that commit 846afbd1 ("GIC: Dont disable INT in ack callback")
broke cascading interrupts by forgetting to add IRQ masking. This is
no longer an issue because the unmask call is now unnecessary.

Tested on Versatile Express and Realview EB (1176 w/ cascaded GICs).

Cc: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 arch/arm/common/gic.c |   23 +++++++++--------------
 1 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/arch/arm/common/gic.c b/arch/arm/common/gic.c
index 2243772..9def30b 100644
--- a/arch/arm/common/gic.c
+++ b/arch/arm/common/gic.c
@@ -71,13 +71,6 @@ static inline unsigned int gic_irq(struct irq_data *d)
 /*
  * Routines to acknowledge, disable and enable interrupts
  */
-static void gic_ack_irq(struct irq_data *d)
-{
-	spin_lock(&irq_controller_lock);
-	writel(gic_irq(d), gic_cpu_base(d) + GIC_CPU_EOI);
-	spin_unlock(&irq_controller_lock);
-}
-
 static void gic_mask_irq(struct irq_data *d)
 {
 	u32 mask = 1 << (d->irq % 32);
@@ -96,6 +89,11 @@ static void gic_unmask_irq(struct irq_data *d)
 	spin_unlock(&irq_controller_lock);
 }
 
+static void gic_eoi_irq(struct irq_data *d)
+{
+	writel(gic_irq(d), gic_cpu_base(d) + GIC_CPU_EOI);
+}
+
 static int gic_set_type(struct irq_data *d, unsigned int type)
 {
 	void __iomem *base = gic_dist_base(d);
@@ -174,9 +172,6 @@ static void gic_handle_cascade_irq(unsigned int irq, struct irq_desc *desc)
 	unsigned int cascade_irq, gic_irq;
 	unsigned long status;
 
-	/* primary controller ack'ing */
-	chip->irq_ack(&desc->irq_data);
-
 	spin_lock(&irq_controller_lock);
 	status = readl(chip_data->cpu_base + GIC_CPU_INTACK);
 	spin_unlock(&irq_controller_lock);
@@ -192,15 +187,15 @@ static void gic_handle_cascade_irq(unsigned int irq, struct irq_desc *desc)
 		generic_handle_irq(cascade_irq);
 
  out:
-	/* primary controller unmasking */
-	chip->irq_unmask(&desc->irq_data);
+	/* primary controller EOI */
+	chip->irq_eoi(&desc->irq_data);
 }
 
 static struct irq_chip gic_chip = {
 	.name			= "GIC",
-	.irq_ack		= gic_ack_irq,
 	.irq_mask		= gic_mask_irq,
 	.irq_unmask		= gic_unmask_irq,
+	.irq_eoi		= gic_eoi_irq,
 	.irq_set_type		= gic_set_type,
 #ifdef CONFIG_SMP
 	.irq_set_affinity	= gic_set_cpu,
@@ -275,7 +270,7 @@ static void __init gic_dist_init(struct gic_chip_data *gic,
 	for (i = irq_start; i < irq_limit; i++) {
 		set_irq_chip(i, &gic_chip);
 		set_irq_chip_data(i, gic);
-		set_irq_handler(i, handle_level_irq);
+		set_irq_handler(i, handle_fasteoi_irq);
 		set_irq_flags(i, IRQF_VALID | IRQF_PROBE);
 	}
 
-- 
1.7.0.4