of: Add of_get_cpu_hwid() to read hardware ID from CPU nodes

There are various open coded implementions parsing the CPU node 'reg'
property which contains the CPU's hardware ID. Introduce a new function,
of_get_cpu_hwid(), to read the hardware ID.

All the callers should be DT only code, so no need for an empty
function.

Cc: Frank Rowand <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>
Tested-by: Florian Fainelli <[e-mail]>
Reviewed-by: Sudeep Holla <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/of/base.c

···
 }
 EXPORT_SYMBOL(of_get_property);
 
+/**
+ * of_get_cpu_hwid - Get the hardware ID from a CPU device node
+ *
+ * @cpun: CPU number(logical index) for which device node is required
+ * @thread: The local thread number to get the hardware ID for.
+ *
+ * Return: The hardware ID for the CPU node or ~0ULL if not found.
+ */
+u64 of_get_cpu_hwid(struct device_node *cpun, unsigned int thread)
+{
+	const __be32 *cell;
+	int ac, len;
+
+	ac = of_n_addr_cells(cpun);
+	cell = of_get_property(cpun, "reg", &len);
+	if (!cell || !ac || ((sizeof(*cell) * ac * (thread + 1)) > len))
+		return ~0ULL;
+
+	cell += ac * thread;
+	return of_read_number(cell, ac);
+}
+
 /*
  * arch_match_cpu_phys_id - Match the given logical CPU and physical id
  *

include/linux/of.h

···
 extern struct device_node *of_get_next_cpu_node(struct device_node *prev);
 extern struct device_node *of_get_cpu_state_node(struct device_node *cpu_node,
 						 int index);
+extern u64 of_get_cpu_hwid(struct device_node *cpun, unsigned int thread);
 
 #define for_each_property_of_node(dn, pp) \
 	for (pp = dn->properties; pp != NULL; pp = pp->next)