[PATCH 2/2] platform/x86: wmi: Fix WMI device naming issue

[Armin Wolf]

When multiple WMI devices with the same GUID are present
inside a given system, the WMI driver core might fail to
register all of them.

Consider the following scenario:

	WMI devices (<GUID>[-<ID>]):
	05901221-D566-11D1-B2F0-00A0C9062910	(on PNP0C14:00)
	05901221-D566-11D1-B2F0-00A0C9062910-1	(on PNP0C14:01)

If the WMI core driver somehow unbinds from PNP0C14:00, the following
will happen upon rebinding:

1. The WMI driver core counts all registered WMI devices with a GUID
   of 05901221-D566-11D1-B2F0-00A0C9062910 (count: 1).

2. The new WMI device will be named
   "05901221-D566-11D1-B2F0-00A0C9062910-1" because another device
   with the same GUID is already registered (on PNP0C14:01).

3. The new WMI device cannot be registered due to a name conflict.

Use a IDA when building the WMI device name to avoid such name
collisions by ensuring that a given WMI device ID is not reused.

Userspace applications using udev for WMI device detection are not
impacted by this change. Additionally userspace applications that do
fully support the existing naming scheme are also not impacted. Only
userspace applications using hardcoded sysfs paths will break.
Introduce a kconfig option for restoring the old naming scheme to
give developers time to fix any compatibility issues.

Tested on a Asus Prime B650-Plus.

Signed-off-by: Armin Wolf <W_Armin@xxxxxx>
---
 drivers/platform/x86/Kconfig |  9 +++++++++
 drivers/platform/x86/wmi.c   | 37 +++++++++++++++++++++++++++++++-----
 2 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig
index e5cbd58a99f3..ddc9bf501428 100644
--- a/drivers/platform/x86/Kconfig
+++ b/drivers/platform/x86/Kconfig
@@ -37,6 +37,15 @@ config ACPI_WMI
 	  It is safe to enable this driver even if your DSDT doesn't define
 	  any ACPI-WMI devices.
 
+config ACPI_WMI_LEGACY_DEVICE_NAMES
+	bool "Use legacy WMI device naming scheme"
+	depends on ACPI_WMI
+	help
+	  Say Y here to force the WMI driver core to use the old WMI device naming
+	  scheme when creating WMI devices. Doing so might be necessary for some
+	  userspace applications but will cause the registration of WMI devices with
+	  the same GUID to fail in some corner cases.
+
 config WMI_BMOF
 	tristate "WMI embedded Binary MOF driver"
 	depends on ACPI_WMI
diff --git a/drivers/platform/x86/wmi.c b/drivers/platform/x86/wmi.c
index e46453750d5f..21b7e54bd7ab 100644
--- a/drivers/platform/x86/wmi.c
+++ b/drivers/platform/x86/wmi.c
@@ -20,6 +20,7 @@
 #include <linux/bits.h>
 #include <linux/build_bug.h>
 #include <linux/device.h>
+#include <linux/idr.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
@@ -74,6 +75,8 @@ struct wmi_guid_count_context {
 	int count;
 };
 
+static DEFINE_IDA(wmi_ida);
+
 /*
  * If the GUID data block is marked as expensive, we must enable and
  * explicitily disable data collection.
@@ -978,6 +981,19 @@ static int guid_count(const guid_t *guid)
 	return context.count;
 }
 
+static int wmi_dev_set_name(struct wmi_block *wblock, int count)
+{
+	if (IS_ENABLED(CONFIG_ACPI_WMI_LEGACY_DEVICE_NAMES)) {
+		if (count)
+			return dev_set_name(&wblock->dev.dev, "%pUL-%d", &wblock->gblock.guid,
+					    count);
+		else
+			return dev_set_name(&wblock->dev.dev, "%pUL", &wblock->gblock.guid);
+	}
+
+	return dev_set_name(&wblock->dev.dev, "%pUL-%d", &wblock->gblock.guid, wblock->dev.dev.id);
+}
+
 static int wmi_create_device(struct device *wmi_bus_dev,
 			     struct wmi_block *wblock,
 			     struct acpi_device *device)
@@ -986,7 +1002,7 @@ static int wmi_create_device(struct device *wmi_bus_dev,
 	struct acpi_device_info *info;
 	acpi_handle method_handle;
 	acpi_status status;
-	int count;
+	int count, ret;
 
 	if (wblock->gblock.flags & ACPI_WMI_EVENT) {
 		wblock->dev.dev.type = &wmi_type_event;
@@ -1057,11 +1073,18 @@ static int wmi_create_device(struct device *wmi_bus_dev,
 	if (count < 0)
 		return count;
 
-	if (count) {
-		dev_set_name(&wblock->dev.dev, "%pUL-%d", &wblock->gblock.guid, count);
+	if (count)
 		set_bit(WMI_GUID_DUPLICATED, &wblock->flags);
-	} else {
-		dev_set_name(&wblock->dev.dev, "%pUL", &wblock->gblock.guid);
+
+	ret = ida_alloc(&wmi_ida, GFP_KERNEL);
+	if (ret < 0)
+		return ret;
+
+	wblock->dev.dev.id = ret;
+	ret = wmi_dev_set_name(wblock, count);
+	if (ret < 0) {
+		ida_free(&wmi_ida, wblock->dev.dev.id);
+		return ret;
 	}
 
 	device_initialize(&wblock->dev.dev);
@@ -1147,6 +1170,7 @@ static int parse_wdg(struct device *wmi_bus_dev, struct platform_device *pdev)
 			dev_err(wmi_bus_dev, "failed to register %pUL\n",
 				&wblock->gblock.guid);
 
+			ida_free(&wmi_ida, wblock->dev.dev.id);
 			put_device(&wblock->dev.dev);
 		}
 	}
@@ -1246,7 +1270,10 @@ static void acpi_wmi_notify_handler(acpi_handle handle, u32 event, void *context
 
 static int wmi_remove_device(struct device *dev, void *data)
 {
+	int id = dev->id;
+
 	device_unregister(dev);
+	ida_free(&wmi_ida, id);
 
 	return 0;
 }
-- 
2.39.5