Re: [PATCH v1 2/5] driver core: Add fw_devlink kernel commandline option

fwnode_operations.add_links allows creating device links from
information provided by firmware.

fwnode_operations.add_links is currently implemented only by
OF/devicetree code and a specific case of efi. However, there's nothing
preventing ACPI or other firmware types from implementing it.

The OF implementation is currently controlled by a kernel commandline
parameter called of_devlink.

Since this feature is generic isn't limited to OF, add a generic
fw_devlink kernel commandline parameter to control this feature across
firmware types.

Signed-off-by: Saravana Kannan <redacted>
---
 .../admin-guide/kernel-parameters.txt         | 18 +++++++++++++
 drivers/base/core.c                           | 27 ++++++++++++++++++-
 include/linux/fwnode.h                        |  2 ++
 3 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index dbc22d684627..29985152b66d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt

@@ -1350,6 +1350,24 @@
                        can be changed at run time by the max_graph_depth file
                        in the tracefs tracing directory. default: 0 (no limit)

+       fw_devlink=     [KNL] Create device links between consumer and supplier
+                       devices by scanning the firmware to infer the
+                       consumer/supplier relationships. This feature is
+                       especially useful when drivers are loaded as modules as
+                       it ensures proper ordering of tasks like device probing
+                       (suppliers first, then consumers), supplier boot state
+                       clean up (only after all consumers have probed),
+                       suspend/resume & runtime PM (consumers first, then
+                       suppliers).
+                       Format: { off | permissive | on | rpm }
+                       off --  Don't create device links from firmware info.
+                       permissive -- Create device links from firmware info
+                               but use it only for ordering boot state clean
+                               up (sync_state() calls).
+                       on --   Create device links from firmware info and use it
+                               to enforce probe and suspend/resume ordering.
+                       rpm --  Like "on", but also use to order runtime PM.
+

        gamecon.map[2|3]=
                        [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
                        support via parallel port (up to 5 devices per port)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index d32a3aefff32..aeaca8a3aad9 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c

@@ -2345,6 +2345,31 @@ static int device_private_init(struct device *dev)
        return 0;
 }

+u32 fw_devlink_flags;
+static int __init fw_devlink_setup(char *arg)
+{
+       if (!arg)
+               return -EINVAL;
+
+       if (strcmp(arg, "off") == 0) {
+               fw_devlink_flags = 0;
+       } else if (strcmp(arg, "permissive") == 0) {
+               fw_devlink_flags = DL_FLAG_SYNC_STATE_ONLY;
+       } else if (strcmp(arg, "on") == 0) {
+               fw_devlink_flags = DL_FLAG_AUTOPROBE_CONSUMER;
+       } else if (strcmp(arg, "rpm") == 0) {
+               fw_devlink_flags = DL_FLAG_AUTOPROBE_CONSUMER |
+                                  DL_FLAG_PM_RUNTIME;
+       }
+       return 0;
+}
+early_param("fw_devlink", fw_devlink_setup);
+
+u32 fw_devlink_get_flags(void)
+{
+       return fw_devlink_flags;
+}
+
 /**
  * device_add - add device to device hierarchy.
  * @dev: device.

@@ -2493,7 +2518,7 @@ int device_add(struct device *dev)
         */
        device_link_add_missing_supplier_links();

-       if (fwnode_has_op(dev->fwnode, add_links)) {
+       if (fw_devlink_flags && fwnode_has_op(dev->fwnode, add_links)) {
                fw_ret = fwnode_call_int_op(dev->fwnode, add_links, dev);
                if (fw_ret == -ENODEV)
                        device_link_wait_for_mandatory_supplier(dev);

diff --git a/include/linux/fwnode.h b/include/linux/fwnode.h
index 8feeb94b8acc..e0abafbb17f8 100644
--- a/include/linux/fwnode.h
+++ b/include/linux/fwnode.h

@@ -170,4 +170,6 @@ struct fwnode_operations {
        } while (false)
 #define get_dev_from_fwnode(fwnode)    get_device((fwnode)->dev)

+extern u32 fw_devlink_get_flags(void);
+
 #endif
--

2.25.0.265.gbab2e86ba0-goog