On Wed, 2013-07-31 at 02:01 +0200, Rafael J. Wysocki wrote: > On Thursday, July 18, 2013 02:16:09 AM Rafael J. Wysocki wrote: > > On Sunday, June 09, 2013 07:01:36 PM Matthew Garrett wrote: > > > Windows 8 introduced new policy for backlight control by pushing it out to > > > graphics drivers. This appears to have coincided with a range of vendors > > > adding Windows 8 checks to their backlight control code which trigger either > > > awkward behaviour (Lenovo) or complete brokenness (some Dells). The simplest > > > thing to do would be to just disable ACPI backlight control entirely if the > > > firmware indicates Windows 8 support, but it's entirely possible that > > > individual graphics drivers might still make use of the ACPI functionality in > > > preference to native control. > > > > > > The first two patches in this series are picked from other patchesets aimed at > > > solving similar problems. The last simply unregisters ACPI backlight control > > > on Windows 8 systems when using an Intel GPU. Similar code could be added to > > > other drivers, but I'm reluctant to do so without further investigation as > > > to the behaviour of the vendor drivers under Windows. > > > > Well, after some more time spent on that, we now have a series of 3 patches > > (different from the $subject one) that we think may be used to address this > > issue. As far as I can say, it has been tested by multiple people whose > > systems have those problems and they generally saw improvement. > > > > It is not my ideal approach, but it seems to be the least intrusive and/or > > with the least amount of possible side effects that we can do right now > > as a general measure (alternatively, we could create a possibly long > > blacklist table of affected systems with different workarounds for them, > > but let's just say that is not overwhelmingly attractive). > > > > [1/3] Make ACPICA export things that we need for checking OSI(Win8). > > > > [2/3] Make acpi_video_device_find_cap() call acpi_video_init_brightness() even > > if it is not going to register the backlight interface (needed for > > Thinkpads). > > > > [3/3] Avoid using ACPI backlight if i915 is in use and the firmware believes > > we are Windows 8. > > > > Many thanks to everyone involved! > > So this didn't work, as we had to revert [3/3], but I think we should try to > make some progress with this nevertheless. A way forward I'm seeing now could > be to > (1) Split the ACPI video driver so that it is possible to register the > backlight control separately from the event interface. > (2) Add a command line option to i915 to make it use the native backlight > control (without registering the ACPI one) if set. Make unset the > default initially. > (3) Fix i915 backlight control issues for all systems known to have them > (that may take a while) and flip the defailt for that option to set when we > think we're ready. > (4) If there still are problem reports, flip the default back to unset and > repeat (3). > > If this converges, everyone will be using the native backlight control by > default and the original problem will go away automatically. > > Thoughts? > > Rafael > > Good idea. I have 3-4 laptops with this problem. I can test, but I don't have devices, on which found regressions (in backlight) in previous patch. -- Igor Gnatenko Fedora release 19 (Schrödinger’s Cat) Linux 3.10.3-300.fc19.x86_64 -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
