<html> <head> <base href="https://bugs.freedesktop.org/"> </head> <body> <div> <a class="bz_bug_link bz_status_NEW " title="NEW - [SKL dmc] Headless mode media transcoding is 20-30% slower comparing to connected monitor use case" href="https://bugs.freedesktop.org/show_bug.cgi?id=100572#c28">Comment # 28</a> on <a class="bz_bug_link bz_status_NEW " title="NEW - [SKL dmc] Headless mode media transcoding is 20-30% slower comparing to connected monitor use case" href="https://bugs.freedesktop.org/show_bug.cgi?id=100572">bug 100572</a> from <a class="email" href="mailto:imre.deak@intel.com" title="Imre Deak <imre.deak@intel.com>"> Imre Deak</a> <pre>(In reply to Tvrtko Ursulin from <a href="show_bug.cgi?id=100572#c27">comment #27</a>) > (In reply to Imre Deak from <a href="show_bug.cgi?id=100572#c26">comment #26</a>) > > (In reply to Tvrtko Ursulin from <a href="show_bug.cgi?id=100572#c25">comment #25</a>) > > > One of the experiments Animesh asked me to do was to look at the state of > > > the DC_STATE_EN register at runtime. > > > > > > It looked that it had reverted to a value other than what was programmed by > > > i915. On top of that, it looked impossible to manually modify it at runtime. > > > > > > The value it is reverting to was DC_STATE_EN_UPTO_DC6, regardless of whether > > > the driver has programmed DC_STATE_EN_UPTO_DC5 or DC_STATE_EN_UPTO_DC5 | > > > DC_STATE_EN_UPTO_DC6. > > > > > > This coupled with a comment in gen9_write_dc_state makes me suspicious > > > whether DMC is not doing things behind the drivers back? > > > > We don't use DC5 on SKL normally only DC6. Did you boot with i915.enable_dc > > set to something non-default? > > Not via the param but on Animesh'es suggestion I had the gen9_write_dc_state > modified to only ever program DC_STATE_EN_UPTO_DC5, if non zero state was > passed in. Even after that the read back from DC_STATE_EN at runtime was > DC_STATE_EN_UPTO_DC6. But during programming the read-back was getting the > programmed value. So I guess some time after the initial programming it gets > modified by someone. And I couldn't find any other place in i915 which would > do it. Which is why I thought it could be DMC. Yes, as I understand there is a firmware bug that prevents using DC5 on SKL. After exiting a low-power DC state it will always "restore" DC_STATE_EN_UPTO_DC6 to DC_STATE_EN regardless of what was programmed there.</pre> </div> <hr> You are receiving this mail because: <ul> <li>You are the QA Contact for the bug.</li> <li>You are on the CC list for the bug.</li> <li>You are the assignee for the bug.</li> </ul> </body> </html>