[Bug 86462] New: 4k monitor at 48hz leads to blank screen

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=86462

            Bug ID: 86462
           Summary: 4k monitor at 48hz leads to blank screen
           Product: DRI
           Version: XOrg git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: delamonpansie at gmail.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 109723
  --> https://bugs.freedesktop.org/attachment.cgi?id=109723&action=edit
boot dmesg

Error description : attemp to drive monitor at 48hz leads to blank screen.
Expected behhavior: working setup, since DP MST should able to drive this.

Hardware: dell e7440 with e-port+ port replicator, IBM T221 monitor. E-port+
replicator Synaptics VMM2320 MST HUB running updated firmware A01.
Monitor connected via two DualDVI ports, each running 1920x2400 resolution.
EDID is overriden with drm_kms_helper.edid_firmware.
kernel version: 3cb89f9 drm-intel-nightly: 2014y-11m-18d-15h-23m-21s UTC
integration manifest

EDID override is not strictly neccecary, because modes are added via xrandr:
xrandr --newmode "1920x2400_32.00"  202.75  1920 2056 2256 2592  2400 2403 2413
2447 -hsync +vsync
xrandr --addmode DP2 1920x2400_32.00
xrandr --addmode DP3 1920x2400_32.00
xrandr --output eDP1 --mode 1920x1080 
xrandr --output DP2 --right-of eDP1 --mode 1920x2400_32.00 
xrandr --output DP3 --right-of DP2 --mode 1920x2400_32.00 

This monitor succesfully works on desktop system with nvidia card with refresh
up to 55Hz, however setting refresh higher than 32Hz when runnig on dell
results in a blank screen. 32hz mode is added and selected via xrandr.

I have noticed that setting 48hz mode leads to follwing error in dmesg:
[drm:drm_dp_check_act_status] failed to get ACT bit 1 after 30 retries

So, made following changes and retried
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
b/drivers/gpu/drm/drm_dp_mst_topology.c
index 5682d7e..9afd0a9 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2405,13 +2405,14 @@ int drm_dp_check_act_status(struct
drm_dp_mst_topology_mgr *mgr)
                count++;
                udelay(100);

-       } while (count < 30);
+       } while (count < 300);

        if (!(status & DP_PAYLOAD_ACT_HANDLED)) {
                DRM_DEBUG_KMS("failed to get ACT bit %d after %d retries\n",
status, count);
                ret = -EINVAL;
                goto fail;
-       }
+       } else
+               DRM_DEBUG_KMS("get ACT bit %d after %d retries\n", status,
count);
        return 0;
 fail:
        return ret;

Still blank screen at 48hz, the dmesg difference is:
-[drm:drm_dp_check_act_status] get ACT bit 3 after 18 retries
+[drm:drm_dp_check_act_status] get ACT bit 3 after 27 retries


Attaching dmesg from nvidia, from 32Hz running ok, from 48Hz with blank screen,
xrandr --verbose

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