On 10/14/2013 11:49 AM, Lennart Poettering wrote:

On Mon, 14.10.13 10:36, Aaron Lu (aaron.lu@intel.com) wrote:

quoted

quoted

- Backlight control doesn't work via ACPI without acpi_osi="!Windows 2012"
- Backlight control doesn't work via ACPI with acpi_osi="!Windows 2012"
- Backlight control doesn't work via EC commands from ideapad-laptop.c

The only way backlight handling is supported on the Yoga 13 is via the
intel video driver.

Since I don't have access to the acpidump of this system, my only
question is, does the firmware has a _OSI("Windows 2012") query in DSDT
table?

Yes, it appears to do that as part of _OSC.

The disassembled DSDT table is here:

http://0pointer.de/public/yoga13-dsdt.dsl

Thanks for the info. The firmware has a _OSI("Windows 2012") query so
should be covered by my patch.

quoted

quoted

Or in other words: the situation for the Yoga 13 is *unrelated* to the
Windows 8 issues, and your patch.

I think they are related...
If the firmware is compatible to Windows 8, then my patch will disable
ACPI video backlight interface to prefer GPU's interface.

OK, that might indeed work.

quoted

quoted

I'll soon send another patch which also blacklists the thing in the
ideapad driver, so that only the intel backlight driver is enabled on
Yoga 13 systems, at which point everything will work fine.

Right, that is needed. And if going with my patch, the ideapad driver
will need to be patched similarly like thinkpad_acpi to add a check of
acpi_video_backlight_support before it decides to register its own
backlight interface.

The ideapad driver currently skips registration of the backlight device
if acpi_video_backlight_support() returns true. is that all you need?

Yes, that's all.

Hmm, regarding your patch series, do you plan to skip the registration
of the acpi backlight device if the "raw" device is supported? I mean,

Yes, that's right.

the intel driver could be compiled as a module (and generally is on the
popular distros), so at the time the ACPI subsystem wants to register
the backlight device and know if a raw backlight device is around it
never will be, so what is the point of that? Or am I missing something?

For systems with Intel i915 GPU, ACPI video will wait for GPU driver to
run first, see drivers/acpi/video.c acpi_video_init, the actual
acpi_video_register function is called by i915 driver in
i915_driver_load due to operation region related stuff. Since all
problematic systems reported so far has an Intel GPU, I'm doing it this
way now. If things change, we can enhance it then.

-Aaron