powerpc/pseries/dlpar: Add device tree nodes for DLPAR IO add

In the powerpc-pseries specific implementation, the IO hotplug
event is handled in the user space (drmgr tool). For the DLPAR
IO ADD, the corresponding device tree nodes and properties will
be added to the device tree after the device enable. The user
space (drmgr tool) uses configure_connector RTAS call with the
DRC index to retrieve the device nodes and updates the device
tree by writing to /proc/ppc64/ofdt. Under system lockdown,
/dev/mem access to allocate buffers for configure_connector RTAS
call is restricted which means the user space can not issue this
RTAS call and also can not access to /proc/ppc64/ofdt. The
pseries implementation need user interaction to power-on and add
device to the slot during the ADD event handling. So adds
complexity if the complete hotplug ADD event handling moved to
the kernel.

To overcome /dev/mem access restriction, this patch extends the
/sys/kernel/dlpar interface and provides ‘dt add index <drc_index>’
to the user space. The drmgr tool uses this interface to update
the device tree whenever the device is added. This interface
retrieves device tree nodes for the corresponding DRC index using
the configure_connector RTAS call and adds new device nodes /
properties to the device tree.

Signed-off-by: Scott Cheloha <cheloha@linux.ibm.com>
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240822025028.938332-3-haren@linux.ibm.com

Author: hmyneni

arch/powerpc/platforms/pseries/dlpar.c

@@ -23,6 +23,7 @@
 #include <linux/uaccess.h>
 #include <asm/rtas.h>
 #include <asm/rtas-work-area.h>
+#include <asm/prom.h>
 
 static struct workqueue_struct *pseries_hp_wq;
 
@@ -261,6 +262,20 @@ int dlpar_detach_node(struct device_node *dn)
 
 	return 0;
 }
+static int dlpar_changeset_attach_cc_nodes(struct of_changeset *ocs,
+					struct device_node *dn)
+{
+	int rc;
+
+	rc = of_changeset_attach_node(ocs, dn);
+
+	if (!rc && dn->child)
+		rc = dlpar_changeset_attach_cc_nodes(ocs, dn->child);
+	if (!rc && dn->sibling)
+		rc = dlpar_changeset_attach_cc_nodes(ocs, dn->sibling);
+
+	return rc;
+}
 
 #define DR_ENTITY_SENSE		9003
 #define DR_ENTITY_PRESENT	1
@@ -327,6 +342,118 @@ int dlpar_unisolate_drc(u32 drc_index)
 	return 0;
 }
 
+static struct device_node *
+get_device_node_with_drc_index(u32 index)
+{
+	struct device_node *np = NULL;
+	u32 node_index;
+	int rc;
+
+	for_each_node_with_property(np, "ibm,my-drc-index") {
+		rc = of_property_read_u32(np, "ibm,my-drc-index",
+					     &node_index);
+		if (rc) {
+			pr_err("%s: %pOF: of_property_read_u32 %s: %d\n",
+			       __func__, np, "ibm,my-drc-index", rc);
+			of_node_put(np);
+			return NULL;
+		}
+
+		if (index == node_index)
+			break;
+	}
+
+	return np;
+}
+
+static struct device_node *
+get_device_node_with_drc_info(u32 index)
+{
+	struct device_node *np = NULL;
+	struct of_drc_info drc;
+	struct property *info;
+	const __be32 *value;
+	u32 node_index;
+	int i, j, count;
+
+	for_each_node_with_property(np, "ibm,drc-info") {
+		info = of_find_property(np, "ibm,drc-info", NULL);
+		if (info == NULL) {
+			/* XXX can this happen? */
+			of_node_put(np);
+			return NULL;
+		}
+		value = of_prop_next_u32(info, NULL, &count);
+		if (value == NULL)
+			continue;
+		value++;
+		for (i = 0; i < count; i++) {
+			if (of_read_drc_info_cell(&info, &value, &drc))
+				break;
+			if (index > drc.last_drc_index)
+				continue;
+			node_index = drc.drc_index_start;
+			for (j = 0; j < drc.num_sequential_elems; j++) {
+				if (index == node_index)
+					return np;
+				node_index += drc.sequential_inc;
+			}
+		}
+	}
+
+	return NULL;
+}
+
+static int dlpar_hp_dt_add(u32 index)
+{
+	struct device_node *np, *nodes;
+	struct of_changeset ocs;
+	int rc;
+
+	/*
+	 * Do not add device node(s) if already exists in the
+	 * device tree.
+	 */
+	np = get_device_node_with_drc_index(index);
+	if (np) {
+		pr_err("%s: Adding device node for index (%d), but "
+				"already exists in the device tree\n",
+				__func__, index);
+		rc = -EINVAL;
+		goto out;
+	}
+
+	np = get_device_node_with_drc_info(index);
+
+	if (!np)
+		return -EIO;
+
+	/* Next, configure the connector. */
+	nodes = dlpar_configure_connector(cpu_to_be32(index), np);
+	if (!nodes) {
+		rc = -EIO;
+		goto out;
+	}
+
+	/*
+	 * Add the new nodes from dlpar_configure_connector() onto
+	 * the device-tree.
+	 */
+	of_changeset_init(&ocs);
+	rc = dlpar_changeset_attach_cc_nodes(&ocs, nodes);
+
+	if (!rc)
+		rc = of_changeset_apply(&ocs);
+	else
+		dlpar_free_cc_nodes(nodes);
+
+	of_changeset_destroy(&ocs);
+
+out:
+	of_node_put(np);
+	return rc;
+}
+
 static int changeset_detach_node_recursive(struct of_changeset *ocs,
 					struct device_node *node)
 {
@@ -394,6 +521,9 @@ static int dlpar_hp_dt(struct pseries_hp_errorlog *phpe)
 	lock_device_hotplug();
 
 	switch (phpe->action) {
+	case PSERIES_HP_ELOG_ACTION_ADD:
+		rc = dlpar_hp_dt_add(drc_index);
+		break;
 	case PSERIES_HP_ELOG_ACTION_REMOVE:
 		rc = dlpar_hp_dt_remove(drc_index);
 		break;