genirq: Allow forcing cpu affinity of interrupts

The current implementation of irq_set_affinity() refuses rightfully to
route an interrupt to an offline cpu.

But there is a special case, where this is actually desired. Some of
the ARM SoCs have per cpu timers which require setting the affinity
during cpu startup where the cpu is not yet in the online mask.

If we can't do that, then the local timer interrupt for the about to
become online cpu is routed to some random online cpu.

The developers of the affected machines tried to work around that
issue, but that results in a massive mess in that timer code.

We have a yet unused argument in the set_affinity callbacks of the irq
chips, which I added back then for a similar reason. It was never
required so it got not used. But I'm happy that I never removed it.

That allows us to implement a sane handling of the above scenario. So
the affected SoC drivers can add the required force handling to their
interrupt chip, switch the timer code to irq_force_affinity() and
things just work.

This does not affect any existing user of irq_set_affinity().

Tagged for stable to allow a simple fix of the affected SoC clock
event drivers.

Reported-and-tested-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Tomasz Figa <t.figa@samsung.com>,
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>,
Cc: Kukjin Kim <kgene.kim@samsung.com>
Cc: linux-arm-kernel@lists.infradead.org,
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20140416143315.717251504@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 6 insertions, 11 deletions

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 2486a4c1a710..d34131ca372b 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -180,7 +180,7 @@ int irq_do_set_affinity(struct irq_data *data, const struct cpumask *mask,
         struct irq_chip *chip = irq_data_get_irq_chip(data);
         int ret;
 
-        ret = chip->irq_set_affinity(data, mask, false);
+        ret = chip->irq_set_affinity(data, mask, force);
         switch (ret) {
         case IRQ_SET_MASK_OK:
                 cpumask_copy(data->affinity, mask);
@@ -192,7 +192,8 @@ int irq_do_set_affinity(struct irq_data *data, const struct cpumask *mask,
         return ret;
 }
 
-int __irq_set_affinity_locked(struct irq_data *data, const struct cpumask *mask)
+int irq_set_affinity_locked(struct irq_data *data, const struct cpumask *mask,
+                            bool force)
 {
         struct irq_chip *chip = irq_data_get_irq_chip(data);
         struct irq_desc *desc = irq_data_to_desc(data);
@@ -202,7 +203,7 @@ int __irq_set_affinity_locked(struct irq_data *data, const struct cpumask *mask)
                 return -EINVAL;
 
         if (irq_can_move_pcntxt(data)) {
-                ret = irq_do_set_affinity(data, mask, false);
+                ret = irq_do_set_affinity(data, mask, force);
         } else {
                 irqd_set_move_pending(data);
                 irq_copy_pending(desc, mask);
@@ -217,13 +218,7 @@ int __irq_set_affinity_locked(struct irq_data *data, const struct cpumask *mask)
         return ret;
 }
 
-/**
- *      irq_set_affinity - Set the irq affinity of a given irq
- *      @irq:           Interrupt to set affinity
- *      @mask:          cpumask
- *
- */
-int irq_set_affinity(unsigned int irq, const struct cpumask *mask)
+int __irq_set_affinity(unsigned int irq, const struct cpumask *mask, bool force)
 {
         struct irq_desc *desc = irq_to_desc(irq);
         unsigned long flags;
@@ -233,7 +228,7 @@ int irq_set_affinity(unsigned int irq, const struct cpumask *mask)
                 return -EINVAL;
 
         raw_spin_lock_irqsave(&desc->lock, flags);
-        ret =  __irq_set_affinity_locked(irq_desc_get_irq_data(desc), mask);
+        ret = irq_set_affinity_locked(irq_desc_get_irq_data(desc), mask, force);
         raw_spin_unlock_irqrestore(&desc->lock, flags);
         return ret;
 }