From: Sudeep KarkadaNagesha <redacted>

Currently different drivers requiring to access cpu device node are
parsing the device tree themselves. Since the ordering in the DT need
not match the logical cpu ordering, the parsing logic needs to consider
that. However, this has resulted in lots of code duplication and in some
cases even incorrect logic.

It's better to consolidate them by adding support for getting cpu
device node for a given logical cpu index in DT core library. However
logical to physical index mapping can be architecture specific.

This patch adds of_get_cpu_node to retrieve a cpu device node for a
given logical cpu index. The default matching of the physical id to the
logical cpu index can be overridden by architecture specific code.

It is recommended to use these helper function only in pre-SMP/early
initialisation stages to retrieve CPU device node pointers in logical
ordering. Once the cpu devices are registered, it can be retrieved
easily from cpu device of_node which avoids unnecessary parsing and
matching.

Acked-by: Rob Herring <redacted>
Signed-off-by: Sudeep KarkadaNagesha <redacted>
---
 drivers/of/base.c  | 72
++++++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/of.h |  6 +++++
 2 files changed, 78 insertions(+)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 5c54279..1e690bf 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c

@@ -230,6 +230,78 @@ const void *of_get_property(const struct

device_node *np, const char *name, }
 EXPORT_SYMBOL(of_get_property);

+/*
+ * arch_match_cpu_phys_id - Match the given logical CPU and physical id
+ *
+ * @cpu: logical index of a cpu
+ * @phys_id: physical identifier of a cpu
+ *
+ * CPU logical to physical index mapping is architecture specific.
+ * However this __weak function provides a default match of physical
+ * id to logical cpu index.
+ *
+ * Returns true if the physical identifier and the logical index
correspond + * to the same cpu, false otherwise.
+ */
+bool __weak arch_match_cpu_phys_id(int cpu, u64 phys_id)
+{
+	return (u32)phys_id == cpu;
+}
+
+/**
+ * of_get_cpu_node - Get device node associated with the given logical
CPU + *
+ * @cpu: CPU number(logical index) for which device node is required
+ *
+ * The main purpose of this function is to retrieve the device node for
the + * given logical CPU index. It should be used to intialize the
of_node in + * cpu device. Once of_node in cpu device is populated, all
the further + * references can use that instead.
+ *
+ * CPU logical to physical index mapping is architecture specific and
is built + * before booting secondary cores. This function uses
arch_match_cpu_phys_id + * which can be overridden by architecture
specific implementation. + *
+ * Returns a node pointer for the logical cpu if found, else NULL.
+ */
+struct device_node *of_get_cpu_node(int cpu)
+{
+	struct device_node *cpun, *cpus;
+	const __be32 *cell;
+	u64 hwid;
+	int ac, prop_len;
+
+	cpus = of_find_node_by_path("/cpus");
+	if (!cpus) {
+		pr_warn("Missing cpus node, bailing out\n");
+		return NULL;
+	}
+
+	if (of_property_read_u32(cpus, "#address-cells", &ac)) {
+		pr_warn("%s: missing #address-cells\n", cpus->full_name);
+		ac = of_n_addr_cells(cpus);