Re: i915 black screen introduced by ACPI changes

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 05 Mar 2013, Chris Li <lkml@chrisli.org> wrote:
> On Mon, Mar 4, 2013 at 3:16 PM, Chris Li <lkml@chrisli.org> wrote:
>>>> Two things to test:
>>>> - Can you please check whether any of the backlight drivers in
>>>> /sys/class/backlight does anything? You need to frob the brightness
>>>> file. Please also list all the drivers you have.
>
> This is the kernel with the ACPI change causing the black screen.
>
> lrwxrwxrwx. 1 root root 0 Mar  4 15:20 acpi_video0 ->
> ../../devices/pci0000:00/0000:00:01.0/0000:01:00.0/backlight/acpi_video0
> lrwxrwxrwx. 1 root root 0 Mar  4 15:20 acpi_video1 ->
> ../../devices/pci0000:00/0000:00:02.0/backlight/acpi_video1
> lrwxrwxrwx. 1 root root 0 Mar  4 15:20 intel_backlight ->
> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight
>
> Here is the interesting part. The brightness and max_brightness is all
> set to 4648,
> However, the actual brightness is 0. The bl_power is also 0. I think
> you are on to some thing.

Hi Chris -

Interesting snippets from your dmesgs:

1) good

[    0.000000] Linux version 3.6.0-rc6+ (chrisl@ideapad.lan) (gcc version 4.7.2 20121109 (Red Hat 4.7.2-8) (GCC) ) #25 SMP Wed Feb 20 12:55:06 PST 2013
...
[    5.341431] [drm:intel_panel_get_max_backlight], max backlight PWM = 4648
[    5.341442] [drm:intel_panel_actually_set_backlight], set backlight PWM = 4648
[    5.342572] [drm:intel_panel_get_max_backlight], max backlight PWM = 4648
[    5.342578] [drm:intel_panel_actually_set_backlight], set backlight PWM = 4648

2) bad

[    0.000000] Linux version 3.8.0-rc7+ (chrisl@ideapad.lan) (gcc version 4.7.2 20121109 (Red Hat 4.7.2-8) (GCC) ) #23 SMP Tue Feb 19 19:24:57 PST 2013
...
[    5.692853] [drm:asle_set_backlight], bclp = 0x800000ff
[    5.692865] [drm:intel_panel_get_max_backlight], max backlight PWM = 4648
[    5.692870] [drm:intel_panel_actually_set_backlight], set backlight PWM = 4648
[    5.693401] [drm:asle_set_backlight], bclp = 0x80000000
[    5.693408] [drm:intel_panel_get_max_backlight], max backlight PWM = 4648
[    5.693413] [drm:intel_panel_actually_set_backlight], set backlight PWM = 0

(We've added another debug print to asle_set_backlight.)

For some reason we get two asle requests in a row. In the good kernel
it's the same request twice, in the bad kernel the second requests is
for 0 backlight. The register dumps seem to confirm this.

Please try a recent kernel, with and without the the bisected bad commit

commit a57f7f9175b8ccbc9df83ac13860488913115de4
Author: Bob Moore <robert.moore@intel.com>
Date:   Fri Aug 17 10:55:02 2012 +0800

    ACPICA: Add Windows8/Server2012 string for _OSI method.

reverted. Is the difference the same? Check reg dumps and dmesgs with
drm.debug=0xe.


Thanks,
Jani.