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    <body><span class="vcard"><a class="email" href="mailto:huax.lu@intel.com" title="lu hua <huax.lu@intel.com>"> <span class="fn">lu hua</span></a>
</span> changed
              <a class="bz_bug_link 
          bz_status_ASSIGNED "
   title="ASSIGNED --- - [BDW bisected]igt/pm_pc8 subcases cause system hang"
   href="https://bugs.freedesktop.org/show_bug.cgi?id=77565">bug 77565</a>
        <br>
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          <tr>
            <th>What</th>
            <th>Removed</th>
            <th>Added</th>
          </tr>

         <tr>
           <td style="text-align:right;">Status</td>
           <td>NEEDINFO
           </td>
           <td>ASSIGNED
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            <b><a class="bz_bug_link 
          bz_status_ASSIGNED "
   title="ASSIGNED --- - [BDW bisected]igt/pm_pc8 subcases cause system hang"
   href="https://bugs.freedesktop.org/show_bug.cgi?id=77565#c6">Comment # 6</a>
              on <a class="bz_bug_link 
          bz_status_ASSIGNED "
   title="ASSIGNED --- - [BDW bisected]igt/pm_pc8 subcases cause system hang"
   href="https://bugs.freedesktop.org/show_bug.cgi?id=77565">bug 77565</a>
              from <span class="vcard"><a class="email" href="mailto:huax.lu@intel.com" title="lu hua <huax.lu@intel.com>"> <span class="fn">lu hua</span></a>
</span></b>
        <pre>
<span class="quote">> 
> Please try the following branch:
> <a href="https://github.com/ideak/linux/commits/bdw-rc6-rpm-fix">https://github.com/ideak/linux/commits/bdw-rc6-rpm-fix</a></span >

Apply this patch fail, test the patch as below:
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 75c1c76..b1b5fd8 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3262,6 +3262,10 @@ int intel_enable_rc6(const struct drm_device *dev)
        if (INTEL_INFO(dev)->gen < 5)
                return 0;

+       /* Disable RC6 on Broadwell for now */
+       if (IS_BROADWELL(dev))
+               return 0;
+
        /* Respect the kernel parameter if it is set */
        if (i915.enable_rc6 >= 0)
                return i915.enable_rc6;

The hang still exists.
output:
IGT-Version: 1.6-g78e4c2b (x86_64) (Linux: 3.15.0-rc2_prts_78d88b_20140425
x86_64)
Runtime PM support: 1
PC8 residency support: 1</pre>
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