On Wed, Jul 17, 2013 at 7:16 PM, Rafael J. Wysocki <rjw@xxxxxxx> 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! I tried this patch series and it's as I expected, it's the same as acpi_backlight=vendor, and the intel backlight driver doesn't work correctly in this machine. If you are actually serious about the mantra of "no user-space regressions", then for this machine at least, you need to use the ACPI backlight with Windows8 OSI disabled, until the intel backlight driver is fixed. My patch does that: http://article.gmane.org/gmane.linux.acpi.devel/60969 -- Felipe Contreras -- 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
