linux-kernel - [PATCH v1 1/3] ACPI: scan: Register platform devices for backlight device objects

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Message-ID: <2335304.iZASKD2KPV@rafael.j.wysocki>
Date: Wed, 10 Dec 2025 15:48:29 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Linux ACPI <linux-acpi@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux PM <linux-pm@...r.kernel.org>,
 Armin Wolf <w_armin@....de>, Hans de Goede <hansg@...nel.org>
Subject:
 [PATCH v1 1/3] ACPI: scan: Register platform devices for backlight device
 objects

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

ACPI device objects associated with backlight interfaces are special
because they are ACPI companions of PCI devices (GPUs), but the
interfaces exposed by them resemble platform device one.

Currently, the ACPI video driver binds to them with the help of a
special "synthetic" device ID regardless of the pairing with the PCI
devices, but since it is generally better to use platform drivers for
handling such interfaces, the plan is to convert that drviver into a
platform one.

However, for this purpose, platform devices corresponding to the
ACPI backlight device objects need to be registered, so update
acpi_bus_attach() to apply the default ACPI enumeration to them
and modify acpi_create_platform_device() to avoid bailing out early
if a "physical" device is already attached to a backlight ACPI device
object.

In addition, update acpi_companion_match() to return a valid struct
acpi_device pointer if the ACPI companion of the given device is a
backlight ACPI device object, which will facilitate driver matching
for platform devices corresponding to those objects.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/acpi/acpi_platform.c |    5 +++--
 drivers/acpi/bus.c           |    3 +++
 drivers/acpi/scan.c          |    3 ++-
 3 files changed, 8 insertions(+), 3 deletions(-)

--- a/drivers/acpi/acpi_platform.c
+++ b/drivers/acpi/acpi_platform.c
@@ -120,7 +120,7 @@ struct platform_device *acpi_create_plat
 	int count;

 	/* If the ACPI node already has a physical device attached, skip it. */
-	if (adev->physical_node_count)
+	if (adev->physical_node_count && !adev->pnp.type.backlight)
 		return NULL;

 	match = acpi_match_acpi_device(forbidden_id_list, adev);
@@ -138,7 +138,8 @@ struct platform_device *acpi_create_plat
 	}

 	INIT_LIST_HEAD(&resource_list);
-	if (adev->device_type == ACPI_BUS_TYPE_DEVICE) {
+	if (adev->device_type == ACPI_BUS_TYPE_DEVICE &&
+	    !adev->pnp.type.backlight) {
 		count = acpi_dev_get_resources(adev, &resource_list, NULL, NULL);
 		if (count < 0)
 			return NULL;
--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c
@@ -761,6 +761,9 @@ const struct acpi_device *acpi_companion
 	if (list_empty(&adev->pnp.ids))
 		return NULL;

+	if (adev->pnp.type.backlight)
+		return adev;
+
 	return acpi_primary_dev_companion(adev, dev);
 }

--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -2320,7 +2320,8 @@ static int acpi_bus_attach(struct acpi_d
 	if (ret < 0)
 		return 0;

-	if (device->pnp.type.platform_id || device->flags.enumeration_by_parent)
+	if (device->pnp.type.platform_id || device->pnp.type.backlight ||
+	    device->flags.enumeration_by_parent)
 		acpi_default_enumeration(device);
 	else
 		acpi_device_set_enumerated(device);