[Bug 86733] New: [hsw DP] DP hot plug monitor discovery takes way too long

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=86733

            Bug ID: 86733
           Summary: [hsw DP] DP hot plug monitor discovery takes way too
                    long
           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: dimitri.j.ledkov at intel.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 110049
  --> https://bugs.freedesktop.org/attachment.cgi?id=110049&action=edit
dp-screen-finding-takes-too-long.txt

I'm attaching a log booted without any screens attached, with drm.debug=7 set
on the kernel command line, and later a screen attached.

[   10.814093] [drm:intel_hpd_irq_handler] hotplug event received, stat
0x00400000, dig 0x10101210
[   10.816202] [drm:drm_dp_i2c_do_msg] native defer
-- " --
[   11.142132] [drm:drm_detect_monitor_audio] Monitor has basic audio support
...
[   11.143836] [drm:drm_dp_i2c_do_msg] native defer
-- " --
[   11.466765] [drm:drm_detect_monitor_audio] Monitor has basic audio support
[   11.467203] [drm:drm_dp_i2c_do_msg] native defer
-- " --
[   11.791475] [drm:drm_dp_i2c_do_msg] native defer
[   11.792287] [drm:drm_add_display_info] DP-1: Assigning EDID-1.4 digital sink
color depth as 8 bpc.

Imho the amount of "[drm:drm_dp_i2c_do_msg] native defer" calls is a lot and
takes too much time.

For example, kernel initialisation takes 1.5s with screen attached (as reported
by systemd-analyse), however it takes ~750ms less if no screen is attached and
as per above the bulk of that time on screen hotplug is spent in talking over
i2c. Also not sure why, but "Monitor has basic audio support" is detected
twice...

This is an Intel NUC Haswell platform.

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