[RFC PATCH 16/49] ARM: GIC: allow reading pending state of a hardware IRQ

[Andre Przywara <andre.przywara@linaro.org>]

To synchronize level triggered interrupts which are mapped into a guest,
we need to update the virtual line level at certain points in time.
For a hardware mapped interrupt the GIC is the only place where we can
easily access this information.
Implement a gic_hw_operations member to return the pending state of a
particular interrupt. Due to hardware limitations this only works for
private interrupts of the current CPU, so there is not CPU field in the
prototype.

Signed-off-by: Andre Przywara <andre.przywara@linaro.org>
---
 xen/arch/arm/gic-v2.c     |  6 ++++++
 xen/arch/arm/gic-v3.c     | 13 +++++++++++++
 xen/arch/arm/gic.c        |  5 +++++
 xen/include/asm-arm/gic.h |  5 +++++
 4 files changed, 29 insertions(+)

diff --git a/xen/arch/arm/gic-v2.c b/xen/arch/arm/gic-v2.c
index 5339f69fbc..30081640ac 100644
--- a/xen/arch/arm/gic-v2.c
+++ b/xen/arch/arm/gic-v2.c
@@ -514,6 +514,11 @@ static unsigned int gicv2_read_apr(int apr_reg)
    return readl_gich(GICH_APR);
 }
 
+bool gicv2_read_pending_state(int irq)
+{
+    return readl_gicd(GICD_ISPENDR + (irq / 32) * 4) & (1U << (irq % 32));
+}
+
 static void gicv2_irq_enable(struct irq_desc *desc)
 {
     unsigned long flags;
@@ -1261,6 +1266,7 @@ const static struct gic_hw_operations gicv2_ops = {
     .write_lr            = gicv2_write_lr,
     .read_vmcr_priority  = gicv2_read_vmcr_priority,
     .read_apr            = gicv2_read_apr,
+    .read_pending_state  = gicv2_read_pending_state,
     .make_hwdom_dt_node  = gicv2_make_hwdom_dt_node,
     .make_hwdom_madt     = gicv2_make_hwdom_madt,
     .get_hwdom_extra_madt_size = gicv2_get_hwdom_extra_madt_size,
diff --git a/xen/arch/arm/gic-v3.c b/xen/arch/arm/gic-v3.c
index 595eaef43a..2cbfeb8e03 100644
--- a/xen/arch/arm/gic-v3.c
+++ b/xen/arch/arm/gic-v3.c
@@ -1081,6 +1081,18 @@ static unsigned int gicv3_read_apr(int apr_reg)
     }
 }
 
+static bool gicv3_read_pending_state(int irq)
+{
+    void __iomem *base;
+
+    if ( irq >= NR_GIC_LOCAL_IRQS)
+        base = GICD + (irq / 32) * 4;
+    else
+        base = GICD_RDIST_SGI_BASE;
+
+    return readl(base + GICD_ISPENDR) & (1U << (irq % 32));
+}
+
 static void gicv3_irq_enable(struct irq_desc *desc)
 {
     unsigned long flags;
@@ -1749,6 +1761,7 @@ static const struct gic_hw_operations gicv3_ops = {
     .write_lr            = gicv3_write_lr,
     .read_vmcr_priority  = gicv3_read_vmcr_priority,
     .read_apr            = gicv3_read_apr,
+    .read_pending_state  = gicv3_read_pending_state,
     .secondary_init      = gicv3_secondary_cpu_init,
     .make_hwdom_dt_node  = gicv3_make_hwdom_dt_node,
     .make_hwdom_madt     = gicv3_make_hwdom_madt,
diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
index dfc2108c4d..ce9ab2367e 100644
--- a/xen/arch/arm/gic.c
+++ b/xen/arch/arm/gic.c
@@ -116,6 +116,11 @@ static void gic_set_irq_priority(struct irq_desc *desc, unsigned int priority)
     gic_hw_ops->set_irq_priority(desc, priority);
 }
 
+bool gic_read_pending_state(int irq)
+{
+    return gic_hw_ops->read_pending_state(irq);
+}
+
 /* Program the GIC to route an interrupt to the host (i.e. Xen)
  * - needs to be called with desc.lock held
  */
diff --git a/xen/include/asm-arm/gic.h b/xen/include/asm-arm/gic.h
index d330860580..d7fd18fd47 100644
--- a/xen/include/asm-arm/gic.h
+++ b/xen/include/asm-arm/gic.h
@@ -244,6 +244,9 @@ void gic_set_active_state(int irq, bool state);
 /* Program the IRQ type into the GIC */
 void gic_set_irq_type(struct irq_desc *desc, unsigned int type);
 
+/* Read the pending state of an interrupt from the distributor. */
+bool gic_read_pending_state(int irq);
+
 /* Program the GIC to route an interrupt */
 extern void gic_route_irq_to_xen(struct irq_desc *desc, unsigned int priority);
 extern int gic_route_irq_to_guest(struct domain *, unsigned int virq,
@@ -376,6 +379,8 @@ struct gic_hw_operations {
     unsigned int (*read_vmcr_priority)(void);
     /* Read APRn register */
     unsigned int (*read_apr)(int apr_reg);
+    /* Query the pending state of an interrupt at the distributor level. */
+    bool (*read_pending_state)(int irq);
     /* Secondary CPU init */
     int (*secondary_init)(void);
     /* Create GIC node for the hardware domain */
-- 
2.14.1


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