[Bug 91845] New: i915 does 2s long DP-link-reset (backlight off) during modeset instead of re-using SimpleFB, stacktrace with i915.fastboot=1

Tue Sep 1 18:57:25 PDT 2015

https://bugs.freedesktop.org/show_bug.cgi?id=91845

            Bug ID: 91845
           Summary: i915 does 2s long DP-link-reset (backlight off) during
                    modeset instead of re-using SimpleFB, stacktrace with
                    i915.fastboot=1
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: o.freyermuth at googlemail.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 118043
  --> https://bugs.freedesktop.org/attachment.cgi?id=118043&action=edit
dmesg from boot with: "pcie_aspm=force i915.fastboot=1 drm.debug=0x06"

Bug description:
System is EFI-booted (via refind), efifb with native resolution is available. 
During modeset, display backlight is turned off for ~2 s, drm.debug=0x06
reveals DP and panel are fully reset. 

Forcing i915.fastboot=1 produces the following messages (from attached dmesg):
...
[    0.528989] [drm:intel_fbdev_init_bios] using BIOS fb for initial console
...
[    0.602811] [drm:intelfb_create] re-using BIOS fb
...
i.e. all fine, but then: 
...
[    0.611868] [drm:intel_edp_backlight_off]
...
...
[    1.813729] [drm:intel_panel_actually_set_backlight] set backlight PWM = 0
[    1.825971] [drm:edp_panel_off] Turn eDP port A panel power off
[    1.825977] [drm:wait_panel_off] Wait for panel power off time
[    2.868867] [drm:intel_psr_enable] PSR not supported by this panel
[    2.868868] [drm:intel_edp_drrs_enable] Panel doesn't support DRRS
[    2.868876] ------------[ cut here ]------------
[    2.868882] WARNING: CPU: 7 PID: 36 at
drivers/gpu/drm/i915/intel_uncore.c:620 hsw_unclaimed_reg_debug+0x65/0x7e()
[    2.868885] [drm:intel_uncore_check_errors] *ERROR* Unclaimed register
before interrupt
[    2.868886] Unclaimed register detected after writing to register 0x68070
[    2.868887] Modules linked in:
[    2.868890] CPU: 7 PID: 36 Comm: kworker/7:0 Not tainted 4.2.0-gentoo #4
[    2.868891] Hardware name: Clevo W230SD                 /powered by
premamod.com, BIOS 1.03.04PM v1 07/09/2015
[    2.868895] Workqueue: events output_poll_execute
[    2.868897]  0000000000000009 ffff88041db639f8 ffffffff8191b0a0
0000000000000001
[    2.868899]  ffff88041db63a48 ffff88041db63a38 ffffffff81052be9
ffff88041db63a38
[    2.868901]  ffffffff8156bd36 ffff88041ae80000 0000000000068070
ffff88041ae80080
[    2.868902] Call Trace:
[    2.868906]  [<ffffffff8191b0a0>] dump_stack+0x45/0x57
[    2.868910]  [<ffffffff81052be9>] warn_slowpath_common+0x9c/0xb6
[    2.868912]  [<ffffffff8156bd36>] ? hsw_unclaimed_reg_debug+0x65/0x7e
[    2.868914]  [<ffffffff81052c44>] warn_slowpath_fmt+0x41/0x43
[    2.868917]  [<ffffffff81082972>] ? arch_local_irq_save+0x15/0x1b
[    2.868919]  [<ffffffff8156bd36>] hsw_unclaimed_reg_debug+0x65/0x7e
[    2.868921]  [<ffffffff8156edfa>] hsw_write32+0xa8/0xca
[    2.868924]  [<ffffffff8157b99e>] intel_update_pipe_size+0xef/0x145
[    2.868926]  [<ffffffff8157ba51>] intel_commit_primary_plane+0x5d/0x83
[    2.868929]  [<ffffffff8159811a>] intel_plane_atomic_update+0x14/0x16
[    2.868932]  [<ffffffff8150bde2>]
drm_atomic_helper_commit_planes_on_crtc+0x112/0x166
[    2.868934]  [<ffffffff81582c63>] __intel_set_mode+0x8b5/0x8e1
[    2.868937]  [<ffffffff81588954>] intel_crtc_set_config+0x3fb/0x4c0
[    2.868940]  [<ffffffff8151b536>] drm_mode_set_config_internal+0x57/0xe3
[    2.868942]  [<ffffffff8150c847>] restore_fbdev_mode+0xb5/0xcf
[    2.868944]  [<ffffffff8150e155>]
drm_fb_helper_restore_fbdev_mode_unlocked+0x22/0x59
[    2.868946]  [<ffffffff8150e1bd>] drm_fb_helper_set_par+0x31/0x35
[    2.868948]  [<ffffffff8150e12c>] drm_fb_helper_hotplug_event+0xa6/0xad
[    2.868950]  [<ffffffff81595623>] intel_fbdev_output_poll_changed+0x19/0x1b
[    2.868952]  [<ffffffff815050d6>] drm_kms_helper_hotplug_event+0x23/0x27
[    2.868954]  [<ffffffff8150522d>] output_poll_execute+0x12d/0x14e
[    2.868956]  [<ffffffff810950d6>] ? lock_timer_base.isra.33+0x42/0x68
[    2.868958]  [<ffffffff81095a58>] ? mod_timer+0x7c/0x83
[    2.868961]  [<ffffffff81065375>] process_one_work+0x152/0x272
[    2.868963]  [<ffffffff8106591c>] worker_thread+0x1eb/0x29a
[    2.868966]  [<ffffffff81065731>] ? rescuer_thread+0x272/0x272
[    2.868968]  [<ffffffff810697fe>] kthread+0xa0/0xa8
[    2.868970]  [<ffffffff8106975e>] ? kthread_parkme+0x1f/0x1f
[    2.868973]  [<ffffffff81921d5f>] ret_from_fork+0x3f/0x70
[    2.868975]  [<ffffffff8106975e>] ? kthread_parkme+0x1f/0x1f
[    2.868976] ---[ end trace abe6cc7ab4fd79a7 ]---
[    2.868989] [drm:intel_uncore_check_errors] *ERROR* Unclaimed register
before interrupt

Stacktrace not observed without i915.fastboot=1, but the 2 seconds with
backlight off during boot are always there (supposedly prolonging the overall
boot time significantly). 

System environment:
-- Gentoo Linux 4.2.0 x86_64
-- Machine: Clevo W230SD (Schenker XMG A305)
-- Display connector: Internal Panel, DP connected

Additional info:
-- Machine has nVidia Optimus (should not be relevant here)

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