xen/riscv: introduce aia_init() and aia_usable()

aia_init() is going to contain all the logic related to AIA initialization.

At the moment, it only checks whether the SSAIA extension is available,
and if so, sets is_aia_usable (which  indicates more than just the
availability of the extension) to true; it also signifies that the necessary
components (to be introduced in follow-up patches) have been initialized.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/riscv/Makefile

@@ -1,3 +1,4 @@
+obj-y += aia.o
 obj-y += aplic.o
 obj-y += cpufeature.o
 obj-y += domain.o

xen/arch/riscv/aia.c

@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <xen/errno.h>
+#include <xen/init.h>
+#include <xen/sections.h>
+#include <xen/types.h>
+
+#include <asm/cpufeature.h>
+
+static bool __ro_after_init _aia_usable;
+
+bool aia_usable(void)
+{
+    return _aia_usable;
+}
+
+void __init aia_init(void)
+{
+    if ( !riscv_isa_extension_available(NULL, RISCV_ISA_EXT_ssaia) )
+        return;
+
+    _aia_usable = true;
+}

xen/arch/riscv/include/asm/aia.h

@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef RISCV_AIA_H
+#define RISCV_AIA_H
+
+bool aia_usable(void);
+
+void aia_init(void);
+
+#endif /* RISCV_AIA_H */

xen/arch/riscv/intc.c

@@ -9,6 +9,7 @@
 #include <xen/lib.h>
 #include <xen/spinlock.h>
 
+#include <asm/aia.h>
 #include <asm/intc.h>
 
 static const struct intc_hw_operations *__ro_after_init intc_hw_ops;
@@ -33,6 +34,8 @@ void __init intc_init(void)
 {
     ASSERT(intc_hw_init_ops && intc_hw_init_ops->init);
 
+    aia_init();
+
     if ( intc_hw_init_ops->init() )
         panic("Failed to initialize the interrupt controller drivers\n");
 }