Zhang Rui wrote:
On Thu, 2009-08-20 at 17:14 +0800, Stefan Bader wrote:
Hardware: Acer 6920G (from a bug report)
Another case of a broken BIOS. In this case there are several definitions for
video bus devices but only one has _DOS and _DOD defined. All other definitions
only have _DOD.
I have seen such kind of BIOS too.
In the past (2.6.27) _ADR was not evaluated to make sure of using a present
video device, but with that bug brightness could be changed.
Now the video bus having _DOS and _DOD is detected as not being present. The
other definitions are not considered because they are lacking the _DOS method.
Using the attached patch, would cause the detection code to consider the other
definitions and has been tested to enable backlight control.
Would this be an acceptable approach?
I think so. I generated a similar patch before, but didn't sent it out
for some reason.
My suggestion is that we should also print out a warning message if _DOS
is missed, what do you think?
Some indication about the problem can't hurt. Probably not in
acpi_is_video_device as that would trigger for even unused devices.
So I added a warning to acpi_video_bus_check for the case when _DOS is missing.
The case of _DOS being present but _DOD not might also be worth a warning but
(though the check in acpi_is_video_device prevented this) would have been
accepted by the current code.
-Stefan
thanks,
rui
From the ACPI spec it rather sounds like
_DOD and _DOS must be present for a device for display switching and _DOS would
indicate possible backlight control as well. So the question might not be so
much is it the right thing than is it safe enough to allow more compatibility
with broken implementations without causing other problems...
-Stefan
--
When all other means of communication fail, try words!
>From 6b483015524f67dee3ae2f08f3c0cef27c9d84c6 Mon Sep 17 00:00:00 2001
From: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
Date: Fri, 21 Aug 2009 11:03:05 +0200
Subject: [PATCH] acpi: video: Loosen strictness of video bus detection code
BugLink: http://bugs.launchpad.net/bugs/333386
Currently a video bus device must (beside other criteria) define _DOD and
_DOS methods to be considered a video device.
Some broken BIOSes prevented working backlight control by only defining both
for one (non-existing bus) and only _DOD for the rest. With this patch in
place the other bus definitions were considered too and backlight control
started to work again.
Signed-off-by: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
---
drivers/acpi/video.c | 7 ++++++-
drivers/acpi/video_detect.c | 2 +-
2 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
index 8851315..acd4636 100644
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -1083,7 +1083,12 @@ static int acpi_video_bus_check(struct acpi_video_bus *video)
*/
/* Does this device support video switching? */
- if (video->cap._DOS) {
+ if (video->cap._DOS || video->cap._DOD) {
+ if (!video->cap._DOS) {
+ printk(KERN_WARNING PREFIX
+ "BIOS bug: %s declares _DOD but not _DOS\n",
+ acpi_device_bid(video->device));
+ }
video->flags.multihead = 1;
status = 0;
}
diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 7cd2b63..bee5e34 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -82,7 +82,7 @@ long acpi_is_video_device(struct acpi_device *device)
return 0;
/* Does this device able to support video switching ? */
- if (ACPI_SUCCESS(acpi_get_handle(device->handle, "_DOD", &h_dummy)) &&
+ if (ACPI_SUCCESS(acpi_get_handle(device->handle, "_DOD", &h_dummy)) ||
ACPI_SUCCESS(acpi_get_handle(device->handle, "_DOS", &h_dummy)))
video_caps |= ACPI_VIDEO_OUTPUT_SWITCHING;
--
1.5.4.3
