[PATCH] ACPI video: print out a warning message when duplicate video bus devices under the same VGA controller are detected

[PATCH] ACPI video: print out a warning message when duplicate video bus devices under the same VGA controller are detected

[Zhang Rui]

Some buggy BIOS exports multiple ACPI video bus devices for the same
VGA controller, and multiple backlight control methods as well.
This may mess up the ACPI video backlight control.
http://bugzilla.kernel.org/show_bug.cgi?id=13577

We should at least send out a warning message in this case.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
---
 drivers/acpi/video.c |   24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

Index: linux-2.6/drivers/acpi/video.c
===================================================================
--- linux-2.6.orig/drivers/acpi/video.c
+++ linux-2.6/drivers/acpi/video.c
@@ -2233,12 +2233,36 @@ static int acpi_video_resume(struct acpi
 	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))
+		printk(KERN_WARNING FW_BUG "Duplicate ACPI video bus "
+				"devices for the same VGA controller\n");
+	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_walk_namespace(ACPI_TYPE_DEVICE, device->parent->handle,
+			    1, acpi_video_bus_match, device, NULL);
+
 	video = kzalloc(sizeof(struct acpi_video_bus), GFP_KERNEL);
 	if (!video)
 		return -ENOMEM;

Re: [PATCH] ACPI video: print out a warning message when duplicate video bus devices under the same VGA controller are detected

[Len Brown]

On Wed, 25 Nov 2009, Zhang Rui wrote:

> 
> Some buggy BIOS exports multiple ACPI video bus devices for the same
> VGA controller, and multiple backlight control methods as well.
> This may mess up the ACPI video backlight control.
> http://bugzilla.kernel.org/show_bug.cgi?id=13577
> 
> We should at least send out a warning message in this case.
> 
> Signed-off-by: Zhang Rui <rui.zhang@intel.com>
> ---
>  drivers/acpi/video.c |   24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> Index: linux-2.6/drivers/acpi/video.c
> ===================================================================
> --- linux-2.6.orig/drivers/acpi/video.c
> +++ linux-2.6/drivers/acpi/video.c
> @@ -2233,12 +2233,36 @@ static int acpi_video_resume(struct acpi
>  	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))
> +		printk(KERN_WARNING FW_BUG "Duplicate ACPI video bus "
> +				"devices for the same VGA controller\n");

what is somebody supposed to _do_ when they see this message?

thanks,
-Len

Re: [PATCH] ACPI video: print out a warning message when duplicate video bus devices under the same VGA controller are detected

[Zhang Rui]

On Thu, 2009-11-26 at 05:39 +0800, Len Brown wrote:
> On Wed, 25 Nov 2009, Zhang Rui wrote:
> 
> > 
> > Some buggy BIOS exports multiple ACPI video bus devices for the same
> > VGA controller, and multiple backlight control methods as well.
> > This may mess up the ACPI video backlight control.
> > http://bugzilla.kernel.org/show_bug.cgi?id=13577
> > 
> > We should at least send out a warning message in this case.
> > 
> > Signed-off-by: Zhang Rui <rui.zhang@intel.com>
> > ---
> >  drivers/acpi/video.c |   24 ++++++++++++++++++++++++
> >  1 file changed, 24 insertions(+)
> > 
> > Index: linux-2.6/drivers/acpi/video.c
> > ===================================================================
> > --- linux-2.6.orig/drivers/acpi/video.c
> > +++ linux-2.6/drivers/acpi/video.c
> > @@ -2233,12 +2233,36 @@ static int acpi_video_resume(struct acpi
> >  	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))
> > +		printk(KERN_WARNING FW_BUG "Duplicate ACPI video bus "
> > +				"devices for the same VGA controller\n");
> 
> what is somebody supposed to _do_ when they see this message?
> 
I think this warning message gives us clues when debugging backlight
issues.
Say we see a bug report that brightness switching doesn't work and find
out that there is such a warning message in the dmesg output, then we
can see which video bus device under this VGA controller actually works.

If this bug is not rare, then we can set up a dmi list to choose the
working video bus device for these laptops.

thanks,
rui

Re: [PATCH] ACPI video: print out a warning message when duplicate video bus devices under the same VGA controller are detected

[Matthew Garrett]

On Thu, Nov 26, 2009 at 09:05:33AM +0800, Zhang Rui wrote:

> If this bug is not rare, then we can set up a dmi list to choose the
> working video bus device for these laptops.

Any time somebody says "we can set up a dmi list", we've already failed. 
Does Windows work on this system without platform-specific drivers? If 
so, Linux is wrong and a dmi approach is incorrect. Does Windows require 
a platform-specific driver? If so, Linux should also require a 
platform-specific driver and a dmi approach in the core code is 
incorrect.

-- 
Matthew Garrett | mjg59@srcf.ucam.org

Re: [PATCH] ACPI video: print out a warning message when duplicate video bus devices under the same VGA controller are detected

[Len Brown]

lets do this:

take this patch and modify it so that by default it fixes the bug
filed in http://bugzilla.kernel.org/show_bug.cgi?id=13577
ie. by default do what Windows 2006 seems to do and use the 1st
and ignore the duplicates.

continue to print out the warning, so we have some clue
how much we see this in the field.

and also modify the patch so that in case we are guessing wrong
about windows compatibility, we go back to current behaviour
and allow multiple devices.  say video.allow_duplicates or something

thanks,
Len Brown, Intel Open Source Technology Center