* RE: [PATCH v2 2/5] software node: add fw_devlink support
From: Bird, Tim @ 2026-07-06 16:55 UTC (permalink / raw)
To: Bartosz Golaszewski; +Cc: Embedded Linux mailing list
In-Reply-To: <20260706-swnode-fw-devlink-v2-2-f39b09d50112@oss.qualcomm.com>
Hey Bartosz,
Can you also please CC: linux-embedded@vger.kernel.org on this patch set, in the future?
There are a few embedded Linux developers working on boot-time for the Linux kernel,
who are interested in this work.
Thanks,
-- Tim
> -----Original Message-----
> From: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
> Sent: Monday, July 6, 2026 6:54 AM
> To: Brendan Higgins <brendan.higgins@linux.dev>; David Gow <david@davidgow.net>; Rae Moar <raemoar63@gmail.com>; Andy
> Shevchenko <andriy.shevchenko@linux.intel.com>; Daniel Scally <djrscally@gmail.com>; Heikki Krogerus <heikki.krogerus@linux.intel.com>;
> Sakari Ailus <sakari.ailus@linux.intel.com>; Bartosz Golaszewski <brgl@kernel.org>; Greg Kroah-Hartman <gregkh@linuxfoundation.org>;
> Rafael J. Wysocki <rafael@kernel.org>; Danilo Krummrich <dakr@kernel.org>; Linus Walleij <linusw@kernel.org>; Dmitry Torokhov
> <dmitry.torokhov@gmail.com>
> Cc: linux-kernel@vger.kernel.org; linux-kselftest@vger.kernel.org; kunit-dev@googlegroups.com; linux-acpi@vger.kernel.org; driver-
> core@lists.linux.dev; linux-gpio@vger.kernel.org; Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
> Subject: [PATCH v2 2/5] software node: add fw_devlink support
>
> Software nodes can be used to describe supplier-consumer relationships between devices they represent using reference property entries.
> Unlike for OF-nodes, driver core cannot yet use these references to create a probe order that avoids needless
>
> Software nodes can be used to describe supplier-consumer relationships
> between devices they represent using reference property entries. Unlike
> for OF-nodes, driver core cannot yet use these references to create a
> probe order that avoids needless probe deferrals on missing providers.
>
> Implement software_node_add_links() modelled on of_fwnode_add_links().
> For every DEV_PROP_REF property we resolve each referenced supplier and
> create an fwnode link from the node to it. The driver core later promotes
> these to device links and defers the consumer until the suppliers are
> ready.
>
> There's no allowlist like the one DT needs - devicetree phandles appear
> in plenty of non-supplier contexts, but a software node only carries a
> reference property when its author explicitly points at another node, so
> we treat every reference as an intentional supplier dependency and link
> all of them. Graph "remote-endpoint" references are skipped for now: they
> go 2-ways between endpoint nodes and would create graph cycles without
> the port-parent lifting DT does via get_con_dev(). References to
> suppliers that aren't registered yet and self-references are ignored.
>
> fw_devlink resolves the supplier device through fwnode->dev but the core
> only records the owning device on the primary fwnode. When the software
> node is a device's secondary fwnode, mirror the device pointer onto it in
> software_node_notify() so the consumer can actually find the supplier
> instead of deferring forever.
>
> While at it: purge the fwnode links in software_node_release() now that
> software nodes can own them.
>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
> ---
> drivers/base/swnode.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 79 insertions(+)
>
> diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
> index 869228a65cb365567ddac7db6ad7b8743e0dbca9..e6e2d6926fef2db82eb1f2bf439e80aacf48668a 100644
> --- a/drivers/base/swnode.c
> +++ b/drivers/base/swnode.c
> @@ -699,6 +699,62 @@ software_node_graph_parse_endpoint(const struct fwnode_handle *fwnode,
> return 0;
> }
>
> +static int software_node_add_links(struct fwnode_handle *fwnode)
> +{
> + const struct software_node_ref_args *ref, *ref_array;
> + struct swnode *swnode = to_swnode(fwnode);
> + const struct property_entry *prop;
> + struct fwnode_handle *refnode;
> + unsigned int count;
> +
> + if (!swnode || !swnode->node->properties)
> + return 0;
> +
> + /*
> + * Unlike Device Tree, where phandles appear in many non-supplier
> + * contexts and a curated allowlist is required, a software node only
> + * carries a DEV_PROP_REF property when the author explicitly describes
> + * a reference to another node. Every such reference is therefore an
> + * intentional supplier dependency, so we create fwnode links for all
> + * of them.
> + */
> + for (prop = swnode->node->properties; prop->name; prop++) {
> + if (prop->type != DEV_PROP_REF || prop->is_inline)
> + continue;
> +
> + /*
> + * TODO: Graph "remote-endpoint" references go both ways
> + * between endpoint child nodes and would create endpoint
> + * cycles. Let's leave it out for now until we have potential
> + * users.
> + */
> + if (!strcmp(prop->name, "remote-endpoint"))
> + continue;
> +
> + ref_array = prop->pointer;
> + count = prop->length / sizeof(*ref_array);
> +
> + for (unsigned int i = 0; i < count; i++) {
> + ref = &ref_array[i];
> +
> + if (ref->swnode)
> + refnode = software_node_fwnode(ref->swnode);
> + else if (ref->fwnode)
> + refnode = ref->fwnode;
> + else
> + continue;
> +
> + /* Supplier not registered yet, or self-reference. */
> + if (!refnode || refnode == &swnode->fwnode)
> + continue;
> +
> + fwnode_link_add(&swnode->fwnode, refnode, 0);
> + }
> + }
> +
> + return 0;
> +}
> +
> static const struct fwnode_operations software_node_ops = {
> .get = software_node_get,
> .put = software_node_put,
> @@ -716,6 +772,7 @@ static const struct fwnode_operations software_node_ops = {
> .graph_get_remote_endpoint = software_node_graph_get_remote_endpoint,
> .graph_get_port_parent = software_node_graph_get_port_parent,
> .graph_parse_endpoint = software_node_graph_parse_endpoint,
> + .add_links = software_node_add_links,
> };
>
> /* -------------------------------------------------------------------------- */
> @@ -787,6 +844,8 @@ static void software_node_release(struct kobject *kobj)
> {
> struct swnode *swnode = kobj_to_swnode(kobj);
>
> + fwnode_links_purge(&swnode->fwnode);
> +
> if (swnode->parent) {
> ida_free(&swnode->parent->child_ids, swnode->id);
> list_del(&swnode->entry);
> @@ -1105,6 +1164,17 @@ void software_node_notify(struct device *dev)
> if (!swnode)
> return;
>
> + /*
> + * When the software node is the device's secondary firmware node,
> + * the core only records the owning device on the primary fwnode
> + * (see device_add()). fw_devlink resolves a supplier device through
> + * fwnode->dev, so without this a consumer referencing the software
> + * node could never find the supplier device and would defer forever.
> + * Make fwnode.dev point to its owner in that case.
> + */
> + if (dev_fwnode(dev) != &swnode->fwnode && !swnode->fwnode.dev)
> + swnode->fwnode.dev = dev;
> +
> swnode_get(swnode);
> ret = sysfs_create_link(&dev->kobj, &swnode->kobj, "software_node");
> if (ret)
> @@ -1127,6 +1197,15 @@ void software_node_notify_remove(struct device *dev)
>
> sysfs_remove_link(&swnode->kobj, dev_name(dev));
> sysfs_remove_link(&dev->kobj, "software_node");
> +
> + /*
> + * Drop the device pointer mirrored onto a secondary software node in
> + * software_node_notify(). For a primary software node the core owns
> + * fwnode->dev and clears it in device_del().
> + */
> + if (dev_fwnode(dev) != &swnode->fwnode && swnode->fwnode.dev == dev)
> + swnode->fwnode.dev = NULL;
> +
> swnode_put(swnode);
>
> if (swnode->managed) {
>
> --
> 2.47.3
>
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