[PATCH v2 4/4] platform/x86: x86-android-tablets: enable fwnode matching of GPIO chips

Bartosz Golaszewski
2026-04-02T12:55:00Z

In order to allow GPIOLIB to match cherryview and baytrail GPIO
controllers by their firmware nodes instead of their names, we need to
attach the - currently "dangling" - existing software nodes to their
target devices dynamically.

We deal with devices described in ACPI so set up a bus notifier waiting
for the ADD events. We know the name of the device we're waiting for so
match against it and - on match - assign the appropriate software node
as the secondary firmware node of the underlying ACPI node. In case the
event was emitted earlier than this driver's probe: also make sure the
device was not added before.

Scheduling fine-grained devres actions allows for proper teardown and
unsetting of the secondary firmware nodes.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
---
drivers/platform/x86/x86-android-tablets/core.c | 127 +++++++++++++++++++++++-
1 file changed, 124 insertions(+), 3 deletions(-)

diff --git a/drivers/platform/x86/x86-android-tablets/core.c b/drivers/platform/x86/x86-android-tablets/core.c
index 021009e9085bec3db9c4daa1f6235600210a6099..9e6e8f272dfe16cda421b569802045c3d94fc0ab 100644
--- a/drivers/platform/x86/x86-android-tablets/core.c
+++ b/drivers/platform/x86/x86-android-tablets/core.c
@@ -13,10 +13,12 @@
#include <linux/acpi.h>
#include <linux/device.h>
#include <linux/dmi.h>
+#include <linux/fwnode.h>
#include <linux/gpio/consumer.h>
#include <linux/gpio/machine.h>
#include <linux/irq.h>
#include <linux/module.h>
+#include <linux/notifier.h>
#include <linux/pci.h>
#include <linux/platform_device.h>
#include <linux/serdev.h>
@@ -360,6 +362,124 @@ static const struct software_node *cherryview_gpiochip_node_group[] = {
NULL
};

+struct auto_secondary_data {
+ struct notifier_block nb;
+ struct device *parent;
+};
+
+static void auto_secondary_unset(void *data)
+{
+ struct fwnode_handle *fwnode = data;
+
+ fwnode->secondary = NULL;
+}
+
+static int acpi_set_secondary_fwnode(struct device *parent, struct device *dev,
+ const struct software_node *const swnode)
+{
+ struct acpi_device *device = to_acpi_device(dev);
+ struct fwnode_handle *fwnode;
+ int ret;
+
+ fwnode = software_node_fwnode(swnode);
+ if (WARN_ON(!fwnode))
+ return -ENOENT;
+
+ fwnode->secondary = ERR_PTR(-ENODEV);
+ device->fwnode.secondary = fwnode;
+
+ ret = devm_add_action_or_reset(parent, auto_secondary_unset, &device->fwnode);
+ if (ret)
+ dev_err(parent, "Failed to schedule the unset action for secondary fwnode\n");
+
+ return ret;
+}
+
+static int acpi_auto_secondary_notifier(struct notifier_block *nb,
+ unsigned long action, void *data)
+{
+ struct auto_secondary_data *auto_sec = container_of(nb, struct auto_secondary_data, nb);
+ const struct software_node *const *swnode;
+ struct device *dev = data;
+ int ret;
+
+ switch (action) {
+ case BUS_NOTIFY_ADD_DEVICE:
+ for (swnode = gpiochip_node_group; *swnode; swnode++) {
+ if (strcmp((*swnode)->name, dev_name(dev)) == 0) {
+ ret = acpi_set_secondary_fwnode(auto_sec->parent, dev, *swnode);
+ return ret ? NOTIFY_BAD : NOTIFY_OK;
+ }
+ }
+ break;
+ default:
+ break;
+ }
+
+ return NOTIFY_DONE;
+}
+
+static void auto_secondary_unregister_node_group(void *data)
+{
+ const struct software_node **nodes = data;
+
+ software_node_unregister_node_group(nodes);
+}
+
+static void auto_secondary_unregister_notifier(void *data)
+{
+ struct notifier_block *nb = data;
+
+ bus_unregister_notifier(&acpi_bus_type, nb);
+}
+
+static int auto_secondary_fwnode_init(struct device *parent)
+{
+ const struct software_node *const *swnode;
+ struct auto_secondary_data *data;
+ int ret;
+
+ ret = software_node_register_node_group(gpiochip_node_group);
+ if (ret)
+ return ret;
+
+ ret = devm_add_action_or_reset(parent,
+ auto_secondary_unregister_node_group,
+ gpiochip_node_group);
+ if (ret)
+ return ret;
+
+ data = devm_kzalloc(parent, sizeof(*data), GFP_KERNEL);
+ if (!data)
+ return -ENOMEM;
+
+ data->nb.notifier_call = acpi_auto_secondary_notifier;
+ data->parent = parent;
+
+ ret = bus_register_notifier(&acpi_bus_type, &data->nb);
+ if (ret)
+ return ret;
+
+ ret = devm_add_action_or_reset(parent,
+ auto_secondary_unregister_notifier,
+ &data->nb);
+ if (ret)
+ return ret;
+
+ /* Device may have been already added. */
+ for (swnode = gpiochip_node_group; *swnode; swnode++) {
+ struct device *dev __free(put_device) =
+ bus_find_device_by_name(&acpi_bus_type, NULL, (*swnode)->name);
+ if (dev) {
+ ret = acpi_set_secondary_fwnode(parent, dev, *swnode);
+ if (ret)
+ return ret;
+ }
+ }
+
+ return 0;
+}
+
static void x86_android_tablet_remove(struct platform_device *pdev)
{
int i;
@@ -391,7 +511,6 @@ static void x86_android_tablet_remove(struct platform_device *pdev)

software_node_unregister_node_group(gpio_button_swnodes);
software_node_unregister_node_group(swnode_group);
- software_node_unregister_node_group(gpiochip_node_group);
}

static __init int x86_android_tablet_probe(struct platform_device *pdev)
@@ -427,9 +546,11 @@ static __init int x86_android_tablet_probe(struct platform_device *pdev)
break;
}

- ret = software_node_register_node_group(gpiochip_node_group);
- if (ret)
+ ret = auto_secondary_fwnode_init(&pdev->dev);
+ if (ret) {
+ x86_android_tablet_remove(pdev);
return ret;
+ }

ret = software_node_register_node_group(dev_info->swnode_group);
if (ret) {

--
2.47.3