On 10/8/21 1:51 PM, Frank Rowand wrote:
> On 10/6/21 7:09 PM, Zev Weiss wrote:
>> 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@xxxxxxxxxxxxxxxxx>
>> ---
>> 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).
>
>> + /*
>> + * 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
>
>> +
>> + 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
>> +
>> rc = sysfs_create_bin_file(&np->kobj, &pp->attr);
>> WARN(rc, "error adding attribute %s to node %pOF\n", pp->name, np);
>> return rc;
>>
>
