| Message ID | 4A8E7022.8000707@canonical.com (mailing list archive) |
|---|---|
| State | RFC, archived |
| Headers | show |
On Fri, 2009-08-21 at 18:00 +0800, Stefan Bader wrote: > 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. how about using printk(KERN_WARNING FW_BUG "blabla")? thanks, rui > 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 > >> > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From 6b483015524f67dee3ae2f08f3c0cef27c9d84c6 Mon Sep 17 00:00:00 2001 From: Stefan Bader <stefan.bader@canonical.com> 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@canonical.com> --- 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