powerpc/pseries/dlpar: Search DRC index from ibm,drc-indexes for IO add

IO hotplug add event is handled in the user space with drmgr tool.
After the device is enabled, the user space uses /sys/kernel/dlpar
interface with “dt add index <drc_index>” to update the device tree.
The kernel interface (dlpar_hp_dt_add()) finds the parent node for
the specified ‘drc_index’ from ibm,drc-info property. The recent FW
provides this property from 2017 onwards. But KVM guest code in
some releases is still using the older SLOF firmware which has
ibm,drc-indexes property instead of ibm,drc-info.

If the ibm,drc-info is not available, this patch adds changes to
search ‘drc_index’ from the indexes array in ibm,drc-indexes
property to support old FW.

Fixes: 02b98ff ("powerpc/pseries/dlpar: Add device tree nodes for DLPAR IO add")
Reported-by: Kowshik Jois <kowsjois@linux.ibm.com>
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Tested-by: Amit Machhiwal <amachhiw@linux.ibm.com>
Reviewed-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250531235002.239213-1-haren@linux.ibm.com

Author: hmyneni

arch/powerpc/platforms/pseries/dlpar.c

@@ -404,6 +404,45 @@ get_device_node_with_drc_info(u32 index)
 	return NULL;
 }
 
+static struct device_node *
+get_device_node_with_drc_indexes(u32 drc_index)
+{
+	struct device_node *np = NULL;
+	u32 nr_indexes, index;
+	int i, rc;
+
+	for_each_node_with_property(np, "ibm,drc-indexes") {
+		/*
+		 * First element in the array is the total number of
+		 * DRC indexes returned.
+		 */
+		rc = of_property_read_u32_index(np, "ibm,drc-indexes",
+				0, &nr_indexes);
+		if (rc)
+			goto out_put_np;
+
+		/*
+		 * Retrieve DRC index from the list and return the
+		 * device node if matched with the specified index.
+		 */
+		for (i = 0; i < nr_indexes; i++) {
+			rc = of_property_read_u32_index(np, "ibm,drc-indexes",
+							i+1, &index);
+			if (rc)
+				goto out_put_np;
+
+			if (drc_index == index)
+				return np;
+		}
+	}
+
+	return NULL;
+
+out_put_np:
+	of_node_put(np);
+	return NULL;
+}
+
 static int dlpar_hp_dt_add(u32 index)
 {
 	struct device_node *np, *nodes;
@@ -423,10 +462,19 @@ static int dlpar_hp_dt_add(u32 index)
 		goto out;
 	}
 
+	/*
+	 * Recent FW provides ibm,drc-info property. So search
+	 * for the user specified DRC index from ibm,drc-info
+	 * property. If this property is not available, search
+	 * in the indexes array from ibm,drc-indexes property.
+	 */
 	np = get_device_node_with_drc_info(index);
 
-	if (!np)
-		return -EIO;
+	if (!np) {
+		np = get_device_node_with_drc_indexes(index);
+		if (!np)
+			return -EIO;
+	}
 
 	/* Next, configure the connector. */
 	nodes = dlpar_configure_connector(cpu_to_be32(index), np);