[Bug 82634] New: [i915] backlight issue on TOSHIBA PORTEGE R830 after suspend/resume

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=82634

          Priority: medium
            Bug ID: 82634
                CC: intel-gfx-bugs at lists.freedesktop.org
          Assignee: intel-gfx-bugs at lists.freedesktop.org
           Summary: [i915] backlight issue on TOSHIBA PORTEGE R830 after
                    suspend/resume
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: sylvain.pasche at gmail.com
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: unspecified
         Component: DRM/Intel
           Product: DRI

Created attachment 104639
  --> https://bugs.freedesktop.org/attachment.cgi?id=104639&action=edit
kernel 3.16 dmesg

I experienced issues with the backlight adjustment after installing Fedora on a
TOSHIBA PORTEGE R830 laptop.

The full detail of the issue is available on
https://bugzilla.redhat.com/show_bug.cgi?id=1126159

To summarize: after booting the Fedora 21 kernel (3.16), 3 backlight interfaces
are available (acpi_video0, intel_backlight, toshiba).
The acpi_video0 and toshiba interfaces are not working after suspend/resume.
Only the intel_backlight can change the backlight value after resume.

Red Hat engineer Hans de Goede suggested as a fix to disable the acpi_video0
and toshiba at the kernel level to keep only the intel_backlight. He built a
patched kernel with that change, but that change keeps the backlight unlit
after suspend/resume (and changing the backlight value through sysfs has no
effect).

So he suggested I open a bug on the Intel driver here.

I did the following tests with the result files in attachment.

1) Boot the Fedora 21 3.16.0 kernel (without X) with drm.debug=0x06
 - do a register intel_reg_dump before suspend
(intel_reg_dump_before_3.16.0-1.fc21.x86_64.txt)
 - suspend/resume, then dump the registers again
(intel_reg_dump_after_3.16.0-1.fc21.x86_64.txt)
 - demsg: dmesg_3.16.0-1.fc21.x86_64.txt

In this case, the backlight is working after suspend / resume (through the
intel interface).

2) Boot the Fedora kernel patched by Hans with a change to disable the
acpi_video0 and toshiba backlight interfaces.
 - register dump before suspend:
intel_reg_dump_before_3.15.9-200.rhbz1126159.fc20.x86_64.txt
 - register dump after resume:
intel_reg_dump_after_3.15.9-200.rhbz1126159.fc20.x86_64.txt
 - dmesg: dmesg_3.15.9-200.rhbz1126159.fc20.x86_64.txt

In this case, the backlight is black after resuming.

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