Comment 3 for bug 1501941

The issue is in git master and bisecting shows it to be this commit:

commit 7d9a74622e5a936e4860fcef8358619bf59adae8
Author: Chris Wilson <email address hidden>
Date: Mon Jun 15 14:16:34 2015 +0100

    sna: Be robust in handling DPMS failures

    If we fail to turn off an output via DPMS, disable the entire CRTC in
    order to blank the output and save the screeen/power.

    Reported-by: Lukas Hejtmanek <email address hidden>
    References: https://bugs.freedesktop.org/show_bug.cgi?id=90179
    Signed-off-by: Chris Wilson <email address hidden>

diff --git a/src/sna/sna_display.c b/src/sna/sna_display.c
index f58eb8d..efc5fc9 100644
--- a/src/sna/sna_display.c
+++ b/src/sna/sna_display.c
@@ -213,7 +213,7 @@ struct sna_output {
  int panel_vdisplay;

  uint32_t dpms_id;
- int dpms_mode;
+ uint8_t dpms_mode;
  struct backlight backlight;
  int backlight_active_level;

@@ -251,6 +251,7 @@ enum { /* XXX copied from hw/xfree86/modes/xf86Crtc.c */
  OPTION_DEFAULT_MODES,
 };

+static void __sna_output_dpms(xf86OutputPtr output, int dpms, int fixup);
 static void sna_crtc_disable_cursor(struct sna *sna, struct sna_crtc *crtc);

 static bool is_zaphod(ScrnInfoPtr scrn)
@@ -936,7 +937,7 @@ sna_crtc_force_outputs_on(xf86CrtcPtr crtc)
   if (output->crtc != crtc)
    continue;

- output->funcs->dpms(output, DPMSModeOn);
+ __sna_output_dpms(output, DPMSModeOn, false);
  }

 #if XF86_CRTC_VERSION >= 3
@@ -966,7 +967,7 @@ sna_crtc_force_outputs_off(xf86CrtcPtr crtc)
   if (output->crtc != crtc)
    continue;

- output->funcs->dpms(output, DPMSModeOff);
+ __sna_output_dpms(output, DPMSModeOff, false);
  }
 }

@@ -1099,7 +1100,7 @@ sna_crtc_apply(xf86CrtcPtr crtc)
    * and we lose track of the user settings.
    */
   if (output->crtc == NULL)
- output->funcs->dpms(output, DPMSModeOff);
+ __sna_output_dpms(output, DPMSModeOff, false);

   if (output->crtc != crtc)
    continue;
@@ -3580,7 +3581,7 @@ sna_output_destroy(xf86OutputPtr output)
 }

 static void
-sna_output_dpms(xf86OutputPtr output, int dpms)
+__sna_output_dpms(xf86OutputPtr output, int dpms, int fixup)
 {
  struct sna *sna = to_sna(output->scrn);
  struct sna_output *sna_output = output->driver_private;
@@ -3607,8 +3608,9 @@ sna_output_dpms(xf86OutputPtr output, int dpms)
  if (sna_output->backlight.iface && dpms != DPMSModeOn) {
   if (old_dpms == DPMSModeOn) {
    sna_output->backlight_active_level = sna_output_backlight_get(output);
- DBG(("%s: saving current backlight %d\n",
- __FUNCTION__, sna_output->backlight_active_level));
+ DBG(("%s(%s:%d): saving current backlight %d\n",
+ __FUNCTION__, output->name, sna_output->id,
+ sna_output->backlight_active_level));
   }
   sna_output->dpms_mode = dpms;
   sna_output_backlight_off(sna_output);
@@ -3618,18 +3620,31 @@ sna_output_dpms(xf86OutputPtr output, int dpms)
      drmModeConnectorSetProperty(sna->kgem.fd,
      sna_output->id,
      sna_output->dpms_id,
- dpms))
- dpms = old_dpms;
+ dpms)) {
+ DBG(("%s(%s:%d): failed to set DPMS to %d (fixup? %d)\n",
+ __FUNCTION__, output->name, sna_output->id, dpms, fixup));
+ if (fixup) {
+ sna_crtc_disable(output->crtc, false);
+ return;
+ }
+ }

  if (sna_output->backlight.iface && dpms == DPMSModeOn) {
- DBG(("%s: restoring previous backlight %d\n",
- __FUNCTION__, sna_output->backlight_active_level));
+ DBG(("%s(%d:%d: restoring previous backlight %d\n",
+ __FUNCTION__, output->name, sna_output->id,
+ sna_output->backlight_active_level));
   sna_output_backlight_on(sna_output);
  }

  sna_output->dpms_mode = dpms;
 }

+static void
+sna_output_dpms(xf86OutputPtr output, int dpms)
+{
+ __sna_output_dpms(output, dpms, true);
+}
+
 static bool
 sna_property_ignore(drmModePropertyPtr prop)
 {
@@ -4438,10 +4453,8 @@ reset:
   sna_output->dpms_mode = sna_output->prop_values[i];
   DBG(("%s: found 'DPMS' (idx=%d, id=%d), initial value=%d\n",
        __FUNCTION__, i, sna_output->dpms_id, sna_output->dpms_mode));
- } else {
- sna_output->dpms_id = -1;
+ } else
   sna_output->dpms_mode = DPMSModeOff;
- }

  sna_output->possible_encoders = possible_encoders;
  sna_output->attached_encoders = attached_encoders;