xen/riscv: dt_processor_hartid() implementation

Implements dt_processor_hartid() to get the hart ID of the given
device tree node and do some checks if CPU is available and given device
tree node has proper riscv,isa property.

As a helper function dt_get_hartid() is introduced to deal specifically
with reg propery of a CPU device node.

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

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

@@ -26,6 +26,10 @@ static inline void set_cpuid_to_hartid(unsigned long cpuid,
 
 void setup_tp(unsigned int cpuid);
 
+struct dt_device_node;
+int dt_processor_hartid(const struct dt_device_node *node,
+                        unsigned long *hartid);
+
 #endif
 
 /*

xen/arch/riscv/smpboot.c

@@ -1,6 +1,9 @@
 #include <xen/cpumask.h>
+#include <xen/device_tree.h>
+#include <xen/errno.h>
 #include <xen/init.h>
 #include <xen/sections.h>
+#include <xen/types.h>
 
 #include <asm/current.h>
 
@@ -14,3 +17,77 @@ void __init smp_prepare_boot_cpu(void)
     cpumask_set_cpu(0, &cpu_possible_map);
     cpumask_set_cpu(0, &cpu_online_map);
 }
+
+/**
+ * dt_get_hartid - Get the hartid from a CPU device node
+ *
+ * @cpun: CPU number(logical index) for which device node is required
+ *
+ * Return: The hartid for the CPU node or ~0UL if not found.
+ */
+static unsigned long dt_get_hartid(const struct dt_device_node *cpun)
+{
+    const __be32 *cell;
+    unsigned int ac;
+    uint32_t len;
+
+    ac = dt_n_addr_cells(cpun);
+    cell = dt_get_property(cpun, "reg", &len);
+
+    /*
+     * If ac > 2, the result may be truncated or meaningless unless
+     * dt_read_number() supports wider integers.
+     *
+     * TODO: drop (ac > 2) when dt_read_number() will support wider
+     *       integers.
+     */
+    if ( !cell || !ac || (ac > 2) || (ac > len / sizeof(*cell)) )
+        return ~0UL;
+
+    return dt_read_number(cell, ac);
+}
+
+/*
+ * Returns the hartid of the given device tree node, or -ENODEV if the node
+ * isn't an enabled and valid RISC-V hart node.
+ */
+int dt_processor_hartid(const struct dt_device_node *node,
+                        unsigned long *hartid)
+{
+    const char *isa;
+    int ret;
+
+    if ( !dt_device_is_compatible(node, "riscv") )
+    {
+        printk("Found incompatible CPU\n");
+        return -ENODEV;
+    }
+
+    *hartid = dt_get_hartid(node);
+    if ( *hartid == ~0UL )
+    {
+        printk("Found CPU without CPU ID\n");
+        return -ENODATA;
+    }
+
+    if ( !dt_device_is_available(node))
+    {
+        printk("CPU with hartid=%#lx is not available\n", *hartid);
+        return -ENODEV;
+    }
+
+    if ( (ret = dt_property_read_string(node, "riscv,isa", &isa)) )
+    {
+        printk("CPU with hartid=%#lx has no \"riscv,isa\" property\n", *hartid);
+        return ret;
+    }
+
+    if ( isa[0] != 'r' || isa[1] != 'v' )
+    {
+        printk("CPU with hartid=%#lx has an invalid ISA of \"%s\"\n", *hartid,
+               isa);
+        return -ENODEV;
+    }
+
+    return 0;
+}