On 10/8/21 1:51 PM, Frank Rowand wrote:

On 10/6/21 7:09 PM, Zev Weiss wrote:

quoted

Nodes marked with this (boolean) property will have a writable status
sysfs file, which can be used to toggle them between "okay" and
"reserved", effectively hot-plugging them.  Note that this will only
be effective for devices on busses that register for OF reconfig
notifications (currently spi, i2c, and platform), and only if
CONFIG_OF_DYNAMIC is enabled.

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
---
 drivers/of/kobj.c | 69 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/drivers/of/kobj.c b/drivers/of/kobj.c
index 378cb421aae1..141ae23f3130 100644
--- a/drivers/of/kobj.c
+++ b/drivers/of/kobj.c

@@ -36,6 +36,69 @@ static ssize_t of_node_property_read(struct file *filp, struct kobject *kobj,
 	return memory_read_from_buffer(buf, count, &offset, pp->value, pp->length);
 }
 
+static ssize_t of_node_status_write(struct file *filp, struct kobject *kobj,
+                                    struct bin_attribute *bin_attr, char *buf,
+                                    loff_t offset, size_t count)
+{
+	int rc;
+	char *newstatus;
+	struct property **deadprev;
+	struct property *newprop = NULL;
+	struct property *oldprop = container_of(bin_attr, struct property, attr);
+	struct device_node *np = container_of(kobj, struct device_node, kobj);
+
+	if (WARN_ON_ONCE(strcmp(oldprop->name, "status")))
+		return -EIO;
+
+	if (offset)
+		return -EINVAL;
+
+	if (sysfs_buf_streq(buf, count, "okay") || sysfs_buf_streq(buf, count, "ok"))
+		newstatus = "okay";
+	else if (sysfs_buf_streq(buf, count, "reserved"))
+		newstatus = "reserved";
+	else if (sysfs_buf_streq(buf, count, "disabled"))
+		newstatus = "disabled";
+	else
+		return -EINVAL;
+
+	if (!strcmp(newstatus, oldprop->value))
+		return count;
+

If the general approach of this patch set is the correct way to provide the desired
functionality (I'm still pondering that), then a version of the following code
probably belongs in drivers/of/dynamic.c so that it is easier to maintain and keep
consistent with other dynamic devicetree updates.  If you look at the code there
that touches deadprops (eg __of_changeset_entry_apply()) you will notice that the
locking issues are more extensive than what is implemented here.

I'm still thinking about how this interacts with other forms of dynamic devicetree
changes (eg drivers/of/dynamic.c and also overlays).

quoted

+	/*
+	 * of_update_property_self() doesn't free replaced properties, so
+	 * rifle through deadprops first to see if there's an equivalent old
+	 * status property we can reuse instead of allocating a new one.
+	 */
+	mutex_lock(&of_mutex);
+	for (deadprev = &np->deadprops; *deadprev; deadprev = &(*deadprev)->next) {
+		struct property *deadprop = *deadprev;
+		if (!strcmp(deadprop->name, "status") &&
+		    deadprop->length == strlen(newstatus) + 1 &&
+		    !strcmp(deadprop->value, newstatus)) {
+			*deadprev = deadprop->next;
+			deadprop->next = NULL;
+			newprop = deadprop;
+			break;
+		}
+	}
+	mutex_unlock(&of_mutex);
+
+	if (!newprop) {
+		newprop = kzalloc(sizeof(*newprop), GFP_KERNEL);
+		if (!newprop)
+			return -ENOMEM;
+
+		newprop->name = oldprop->name;
+		newprop->value = newstatus;
+		newprop->length = strlen(newstatus) + 1;
+	}
+
+	rc = of_update_property_self(np, newprop, true);

-Frank

quoted

+
+	return rc ? rc : count;
+}
+
 /* always return newly allocated name, caller must free after use */
 static const char *safe_name(struct kobject *kobj, const char *orig_name)
 {

@@ -79,6 +142,12 @@ int __of_add_property_sysfs(struct device_node *np, struct property *pp)
 	pp->attr.size = secure ? 0 : pp->length;
 	pp->attr.read = of_node_property_read;
 
+	if (!strcmp(pp->name, "status") && of_property_read_bool(np, "dynamic")) {
+		pp->attr.attr.mode |= 0200;
+		pp->attr.write = of_node_status_write;
+		pp->attr.growable = true;
+	}

This isn't (yet) a request for a change to the patch, but more exposing a
potential issue of interaction with overlays.

The current in tree instances of updating a property value are fairly
limited.  Adding a userspace interface to update a property value
(although limited to only a node's status value) has me thinking about
the interaction with dynamic devicetree updates (of/overlay/dynamic.c)
and also overlays.

If a node exists in a base devicetree, containing only the property
"status", then an overlay subsequently populates the node with a
"dynamic" property then the sysfs status file will not be updated
to be writable.  If we do not allow an overlay to add a property
to an existing node, then not an issue.  But we have not created
such overlay rules yet.

Again, not a request for a change to this patch yet, just leaving
a breadcrumb for myself.

-Frank

quoted

+
 	rc = sysfs_create_bin_file(&np->kobj, &pp->attr);
 	WARN(rc, "error adding attribute %s to node %pOF\n", pp->name, np);
 	return rc;