genirq: Allow the irqchip state of an IRQ to be save/restored

There is a number of cases where a kernel subsystem may want to
introspect the state of an interrupt at the irqchip level:

- When a peripheral is shared between virtual machines,
  its interrupt state becomes part of the guest's state,
  and must be switched accordingly. KVM on arm/arm64 requires
  this for its guest-visible timer
- Some GPIO controllers seem to require peeking into the
  interrupt controller they are connected to to report
  their internal state

This seem to be a pattern that is common enough for the core code
to try and support this without too many horrible hacks. Introduce
a pair of accessors (irq_get_irqchip_state/irq_set_irqchip_state)
to retrieve the bits that can be of interest to another subsystem:
pending, active, and masked.

- irq_get_irqchip_state returns the state of the interrupt according
  to a parameter set to IRQCHIP_STATE_PENDING, IRQCHIP_STATE_ACTIVE,
  IRQCHIP_STATE_MASKED or IRQCHIP_STATE_LINE_LEVEL.
- irq_set_irqchip_state similarly sets the state of the interrupt.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Tested-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Phong Vo <pvo@apm.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Tin Huynh <tnhuynh@apm.com>
Cc: Y Vo <yvo@apm.com>
Cc: Toan Le <toanle@apm.com>
Cc: Bjorn Andersson <bjorn@kryo.se>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Link: http://lkml.kernel.org/r/1426676484-21812-2-git-send-email-marc.zyngier@arm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

3 files changed, 111 insertions, 0 deletions

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 150dde04cf4f..950ae4501826 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -361,6 +361,20 @@ static inline int disable_irq_wake(unsigned int irq)
         return irq_set_irq_wake(irq, 0);
 }
 
+/*
+ * irq_get_irqchip_state/irq_set_irqchip_state specific flags
+ */
+enum irqchip_irq_state {
+        IRQCHIP_STATE_PENDING,          /* Is interrupt pending? */
+        IRQCHIP_STATE_ACTIVE,           /* Is interrupt in progress? */
+        IRQCHIP_STATE_MASKED,           /* Is interrupt masked? */
+        IRQCHIP_STATE_LINE_LEVEL,       /* Is IRQ line high? */
+};
+
+extern int irq_get_irqchip_state(unsigned int irq, enum irqchip_irq_state which,
+                                 bool *state);
+extern int irq_set_irqchip_state(unsigned int irq, enum irqchip_irq_state which,
+                                 bool state);
 
 #ifdef CONFIG_IRQ_FORCED_THREADING
 extern bool force_irqthreads;
diff --git a/include/linux/irq.h b/include/linux/irq.h
index d09ec7a1243e..77dd2e7f93f4 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -30,6 +30,7 @@
 struct seq_file;
 struct module;
 struct msi_msg;
+enum irqchip_irq_state;
 
 /*
  * IRQ line status.
@@ -324,6 +325,8 @@ static inline irq_hw_number_t irqd_to_hwirq(struct irq_data *d)
  *                              irq_request_resources
  * @irq_compose_msi_msg:        optional to compose message content for MSI
  * @irq_write_msi_msg:  optional to write message content for MSI
+ * @irq_get_irqchip_state:      return the internal state of an interrupt
+ * @irq_set_irqchip_state:      set the internal state of a interrupt
  * @flags:              chip specific flags
  */
 struct irq_chip {
@@ -363,6 +366,9 @@ struct irq_chip {
         void            (*irq_compose_msi_msg)(struct irq_data *data, struct msi_msg *msg);
         void            (*irq_write_msi_msg)(struct irq_data *data, struct msi_msg *msg);
 
+        int             (*irq_get_irqchip_state)(struct irq_data *data, enum irqchip_irq_state which, bool *state);
+        int             (*irq_set_irqchip_state)(struct irq_data *data, enum irqchip_irq_state which, bool state);
+
         unsigned long   flags;
 };
 
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index c0a1100d911f..e68932bb308e 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1798,3 +1798,94 @@ int request_percpu_irq(unsigned int irq, irq_handler_t handler,
 
         return retval;
 }
+
+/**
+ *      irq_get_irqchip_state - returns the irqchip state of a interrupt.
+ *      @irq: Interrupt line that is forwarded to a VM
+ *      @which: One of IRQCHIP_STATE_* the caller wants to know about
+ *      @state: a pointer to a boolean where the state is to be storeed
+ *
+ *      This call snapshots the internal irqchip state of an
+ *      interrupt, returning into @state the bit corresponding to
+ *      stage @which
+ *
+ *      This function should be called with preemption disabled if the
+ *      interrupt controller has per-cpu registers.
+ */
+int irq_get_irqchip_state(unsigned int irq, enum irqchip_irq_state which,
+                          bool *state)
+{
+        struct irq_desc *desc;
+        struct irq_data *data;
+        struct irq_chip *chip;
+        unsigned long flags;
+        int err = -EINVAL;
+
+        desc = irq_get_desc_buslock(irq, &flags, 0);
+        if (!desc)
+                return err;
+
+        data = irq_desc_get_irq_data(desc);
+
+        do {
+                chip = irq_data_get_irq_chip(data);
+                if (chip->irq_get_irqchip_state)
+                        break;
+#ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
+                data = data->parent_data;
+#else
+                data = NULL;
+#endif
+        } while (data);
+
+        if (data)
+                err = chip->irq_get_irqchip_state(data, which, state);
+
+        irq_put_desc_busunlock(desc, flags);
+        return err;
+}
+
+/**
+ *      irq_set_irqchip_state - set the state of a forwarded interrupt.
+ *      @irq: Interrupt line that is forwarded to a VM
+ *      @which: State to be restored (one of IRQCHIP_STATE_*)
+ *      @val: Value corresponding to @which
+ *
+ *      This call sets the internal irqchip state of an interrupt,
+ *      depending on the value of @which.
+ *
+ *      This function should be called with preemption disabled if the
+ *      interrupt controller has per-cpu registers.
+ */
+int irq_set_irqchip_state(unsigned int irq, enum irqchip_irq_state which,
+                          bool val)
+{
+        struct irq_desc *desc;
+        struct irq_data *data;
+        struct irq_chip *chip;
+        unsigned long flags;
+        int err = -EINVAL;
+
+        desc = irq_get_desc_buslock(irq, &flags, 0);
+        if (!desc)
+                return err;
+
+        data = irq_desc_get_irq_data(desc);
+
+        do {
+                chip = irq_data_get_irq_chip(data);
+                if (chip->irq_set_irqchip_state)
+                        break;
+#ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
+                data = data->parent_data;
+#else
+                data = NULL;
+#endif
+        } while (data);
+
+        if (data)
+                err = chip->irq_set_irqchip_state(data, which, val);
+
+        irq_put_desc_busunlock(desc, flags);
+        return err;
+}