[PATCH 31/37] xen/arm: introduce a helper to parse device tree NUMA distance map

[Wei Chen <wei.chen@xxxxxxx>]

A NUMA aware device tree will provide a "distance-map" node to
describe distance between any two nodes. This patch introduce a
new helper to parse this distance map.

Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
---
 xen/arch/arm/numa_device_tree.c | 106 ++++++++++++++++++++++++++++++++
 1 file changed, 106 insertions(+)

diff --git a/xen/arch/arm/numa_device_tree.c b/xen/arch/arm/numa_device_tree.c
index 7918a397fa..e7fa84df4c 100644
--- a/xen/arch/arm/numa_device_tree.c
+++ b/xen/arch/arm/numa_device_tree.c
@@ -136,3 +136,109 @@ static int __init fdt_parse_numa_memory_node(const void 
*fdt, int node,
 
     return 0;
 }
+
+
+/* Parse NUMA distance map v1 */
+static int __init fdt_parse_numa_distance_map_v1(const void *fdt, int node)
+{
+    const struct fdt_property *prop;
+    const __be32 *matrix;
+    uint32_t entry_count;
+    int len, i;
+
+    printk(XENLOG_INFO "NUMA: parsing numa-distance-map\n");
+
+    prop = fdt_get_property(fdt, node, "distance-matrix", &len);
+    if ( !prop )
+    {
+        printk(XENLOG_WARNING
+               "NUMA: No distance-matrix property in distance-map\n");
+
+        return -EINVAL;
+    }
+
+    if ( len % sizeof(uint32_t) != 0 )
+    {
+        printk(XENLOG_WARNING
+               "distance-matrix in node is not a multiple of u32\n");
+        return -EINVAL;
+    }
+
+    entry_count = len / sizeof(uint32_t);
+    if ( entry_count == 0 )
+    {
+        printk(XENLOG_WARNING "NUMA: Invalid distance-matrix\n");
+
+        return -EINVAL;
+    }
+
+    matrix = (const __be32 *)prop->data;
+    for ( i = 0; i + 2 < entry_count; i += 3 )
+    {
+        uint32_t from, to, distance, opposite;
+
+        from = dt_next_cell(1, &matrix);
+        to = dt_next_cell(1, &matrix);
+        distance = dt_next_cell(1, &matrix);
+        if ( (from == to && distance != NUMA_LOCAL_DISTANCE) ||
+            (from != to && distance <= NUMA_LOCAL_DISTANCE) )
+        {
+            printk(XENLOG_WARNING
+                   "NUMA: Invalid distance: NODE#%u->NODE#%u:%u\n",
+                   from, to, distance);
+            return -EINVAL;
+        }
+
+        printk(XENLOG_INFO "NUMA: distance: NODE#%u->NODE#%u:%u\n",
+               from, to, distance);
+
+        /* Get opposite way distance */
+        opposite = __node_distance(from, to);
+        if ( opposite == 0 )
+        {
+            /* Bi-directions are not set, set both */
+            numa_set_distance(from, to, distance);
+            numa_set_distance(to, from, distance);
+        }
+        else
+        {
+            /*
+             * Opposite way distance has been set to a different value.
+             * It may be a firmware device tree bug?
+             */
+            if ( opposite != distance )
+            {
+                /*
+                 * In device tree NUMA distance-matrix binding:
+                 * 
https://www.kernel.org/doc/Documentation/devicetree/bindings/numa.txt
+                 * There is a notes mentions:
+                 * "Each entry represents distance from first node to
+                 *  second node. The distances are equal in either
+                 *  direction."
+                 *
+                 * That means device tree doesn't permit this case.
+                 * But in ACPI spec, it cares to specifically permit this
+                 * case:
+                 * "Except for the relative distance from a System Locality
+                 *  to itself, each relative distance is stored twice in the
+                 *  matrix. This provides the capability to describe the
+                 *  scenario where the relative distances for the two
+                 *  directions between System Localities is different."
+                 *
+                 * That means a real machine allows such NUMA configuration.
+                 * So, place a WARNING here to notice system administrators,
+                 * is it the specail case that they hijack the device tree
+                 * to support their rare machines?
+                 */
+                printk(XENLOG_WARNING
+                       "Un-matched bi-direction! NODE#%u->NODE#%u:%u, 
NODE#%u->NODE#%u:%u\n",
+                       from, to, distance, to, from, opposite);
+            }
+
+            /* Opposite way distance has been set, just set this way */
+            numa_set_distance(from, to, distance);
+        }
+    }
+
+    return 0;
+}
-- 
2.25.1