[PATCH v2 15/16] xen/riscv: implement setup_irq()

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

Introduce support for IRQ setup on RISC-V by implementing setup_irq() and
__setup_irq(), adapted and extended from an initial implementation by [1].

__setup_irq() does the following:
  - Sets up an IRQ action.
  - Validates that shared IRQs have non-NULL `dev_id` and are only used when
    existing handlers allow sharing.
  - Uses smp_wmb() to enforce memory ordering after assigning desc->action
    to ensure visibility before enabling the IRQ.
  - Supports multi-action setups via CONFIG_IRQ_HAS_MULTIPLE_ACTION.

setup_irq() does the following:
  - Converts IRQ number to descriptor and acquires its lock.
  - Rejects registration if the IRQ is already assigned to a guest domain,
    printing an error.
  - Delegates the core setup to __setup_irq().
  - On first-time setup, disables the IRQ, routes it to Xen using
    intc_route_irq_to_xen(), sets default CPU affinity (current CPU),
    calls the handler’s startup routine, and finally enables the IRQ.

irq_set_affinity() invokes set_affinity() callback from the IRQ handler
if present.

Defined IRQ_NO_PRIORITY as default priority used when routing IRQs to Xen.

[1] 
https://gitlab.com/xen-project/people/olkur/xen/-/commit/7390e2365828b83e27ead56b03114a56e3699dd5

Co-developed-by: Romain Caritey <Romain.Caritey@xxxxxxxxxxxxx>
Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
Changes in V2:
 - Added implenmtation of aplic_set_irq_type() as it is going to be used in
   this commit. And also, update the implementation of it. Make default case
   of switch to do panic().
 - Move all forward declaration up  in asm/irq.h.
 - s/__setup_irq/_setup_irq.
 - Code style fixes.
 - Update commit message.
 - use smp_wmb() instead of smp_mb() in _setup_irq().
 - Drop irq_set_affinity().
 - Use plain C operator instead if {clear,set}_bit() for desc->status as it
   is always used under spinlock().
 - Drop set_bit(_IRQ_DISABLED, &desc->status) in setup_irq() as in the case
   when IRQ is setuped for a first time, desc->status should be already set
   to IRQ_DISABLED in init_one_irq_desc().
----
 xen/arch/riscv/include/asm/irq.h |  2 +
 xen/arch/riscv/irq.c             | 84 ++++++++++++++++++++++++++++++++
 2 files changed, 86 insertions(+)

diff --git a/xen/arch/riscv/include/asm/irq.h b/xen/arch/riscv/include/asm/irq.h
index 1a05c5ff88..d35fac0a86 100644
--- a/xen/arch/riscv/include/asm/irq.h
+++ b/xen/arch/riscv/include/asm/irq.h
@@ -9,6 +9,8 @@
 
 #define NR_IRQS 1024
 
+#define IRQ_NO_PRIORITY 0
+
 /* TODO */
 #define nr_irqs 0U
 #define nr_static_irqs 0
diff --git a/xen/arch/riscv/irq.c b/xen/arch/riscv/irq.c
index 056bdf3ca8..969e22395d 100644
--- a/xen/arch/riscv/irq.c
+++ b/xen/arch/riscv/irq.c
@@ -7,6 +7,7 @@
  */
 
 #include <xen/bug.h>
+#include <xen/cpumask.h>
 #include <xen/device_tree.h>
 #include <xen/errno.h>
 #include <xen/init.h>
@@ -58,6 +59,89 @@ int platform_get_irq(const struct dt_device_node *device, 
int index)
     return dt_irq.irq;
 }
 
+static int _setup_irq(struct irq_desc *desc, unsigned int irqflags,
+                      struct irqaction *new)
+{
+    bool shared = irqflags & IRQF_SHARED;
+
+    ASSERT(new != NULL);
+
+    /*
+     * Sanity checks:
+     *  - if the IRQ is marked as shared
+     *  - dev_id is not NULL when IRQF_SHARED is set
+     */
+    if ( desc->action != NULL && (!(desc->status & IRQF_SHARED) || !shared) )
+        return -EINVAL;
+    if ( shared && new->dev_id == NULL )
+        return -EINVAL;
+
+    if ( shared )
+        desc->status |= IRQF_SHARED;
+
+#ifdef CONFIG_IRQ_HAS_MULTIPLE_ACTION
+    new->next = desc->action;
+#endif
+
+    desc->action = new;
+    smp_wmb();
+
+    return 0;
+}
+
+int setup_irq(unsigned int irq, unsigned int irqflags, struct irqaction *new)
+{
+    int rc;
+    unsigned long flags;
+    struct irq_desc *desc = irq_to_desc(irq);
+    bool disabled;
+
+    spin_lock_irqsave(&desc->lock, flags);
+
+    disabled = (desc->action == NULL);
+
+    if ( desc->status & IRQ_GUEST )
+    {
+        spin_unlock_irqrestore(&desc->lock, flags);
+        /*
+         * TODO: would be nice to have functionality to print which domain owns
+         *       an IRQ.
+         */
+        printk(XENLOG_ERR "ERROR: IRQ %u is already in use by a domain\n", 
irq);
+        return -EBUSY;
+    }
+
+    rc = _setup_irq(desc, irqflags, new);
+    if ( rc )
+        goto err;
+
+    /* First time the IRQ is setup */
+    if ( disabled )
+    {
+        /* Route interrupt to xen */
+        intc_route_irq_to_xen(desc, IRQ_NO_PRIORITY);
+
+        /*
+         * We don't care for now which CPU will receive the
+         * interrupt.
+         *
+         * TODO: Handle case where IRQ is setup on different CPU than
+         *       the targeted CPU and the priority.
+         */
+        desc->handler->set_affinity(desc, cpumask_of(smp_processor_id()));
+
+        desc->handler->startup(desc);
+
+        /* Enable irq */
+        desc->status &= ~IRQ_DISABLED;
+    }
+
+ err:
+    spin_unlock_irqrestore(&desc->lock, flags);
+
+    return rc;
+}
+
 int arch_init_one_irq_desc(struct irq_desc *desc)
 {
     desc->arch.type = IRQ_TYPE_INVALID;
-- 
2.49.0