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<b><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#c27">Comment # 27</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 <span class="vcard"><a class="email" href="mailto:tvrtko.ursulin@linux.intel.com" title="Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>"> <span class="fn">Tvrtko Ursulin</span></a>
</span></b>
<pre>(In reply to Imre Deak from <a href="show_bug.cgi?id=100572#c26">comment #26</a>)
<span class="quote">> (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?</span >
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.</pre>
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