ACPI video: Prune dupe video devices, unless "video.allow_duplicates"

Some buggy BIOS exports multiple ACPI video bus devices for the same
VGA controller, and multiple backlight control methods as well.
This messes up the ACPI video backlight control.

http://bugzilla.kernel.org/show_bug.cgi?id=13577

With this patch applied, only the FIRST ACPI video bus device
under a PCI device node is bind to ACPI video driver by default.

If the first ACPI video bus device doesn't work well, we can use
video.allow_duplicates=1 to go back to the old behavior.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
index 05dff631591..45e6a29c817 100644
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -78,6 +78,13 @@ MODULE_LICENSE("GPL");
 static int brightness_switch_enabled = 1;
 module_param(brightness_switch_enabled, bool, 0644);
 
+/*
+ * By default, we don't allow duplicate ACPI video bus devices
+ * under the same VGA controller
+ */
+static int allow_duplicates;
+module_param(allow_duplicates, bool, 0644);
+
 static int register_count = 0;
 static int acpi_video_bus_add(struct acpi_device *device);
 static int acpi_video_bus_remove(struct acpi_device *device, int type);
@@ -2233,11 +2240,47 @@ static int acpi_video_resume(struct acpi_device *device)
         return AE_OK;
 }
 
+static acpi_status
+acpi_video_bus_match(acpi_handle handle, u32 level, void *context,
+                        void **return_value)
+{
+        struct acpi_device *device = context;
+        struct acpi_device *sibling;
+        int result;
+
+        if (handle == device->handle)
+                return AE_CTRL_TERMINATE;
+
+        result = acpi_bus_get_device(handle, &sibling);
+        if (result)
+                return AE_OK;
+
+        if (!strcmp(acpi_device_name(sibling), ACPI_VIDEO_BUS_NAME))
+                        return AE_ALREADY_EXISTS;
+
+        return AE_OK;
+}
+
 static int acpi_video_bus_add(struct acpi_device *device)
 {
         struct acpi_video_bus *video;
         struct input_dev *input;
         int error;
+        acpi_status status;
+
+        status = acpi_walk_namespace(ACPI_TYPE_DEVICE,
+                                device->parent->handle, 1,
+                                acpi_video_bus_match, NULL,
+                                device, NULL);
+        if (status == AE_ALREADY_EXISTS) {
+                printk(KERN_WARNING FW_BUG
+                        "Duplicate ACPI video bus devices for the"
+                        " same VGA controller, please try module "
+                        "parameter \"video.allow_duplicates=1\""
+                        "if the current driver doesn't work.\n");
+                if (!allow_duplicates)
+                        return -ENODEV;
+        }
 
         video = kzalloc(sizeof(struct acpi_video_bus), GFP_KERNEL);
         if (!video)