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<b><a class="bz_bug_link
bz_status_NEEDINFO "
title="NEEDINFO - [HSW] linux next-20170407+ boots to a blank screen"
href="https://bugs.freedesktop.org/show_bug.cgi?id=100755#c19">Comment # 19</a>
on <a class="bz_bug_link
bz_status_NEEDINFO "
title="NEEDINFO - [HSW] linux next-20170407+ boots to a blank screen"
href="https://bugs.freedesktop.org/show_bug.cgi?id=100755">bug 100755</a>
from <span class="vcard"><a class="email" href="mailto:jani.nikula@intel.com" title="Jani Nikula <jani.nikula@intel.com>"> <span class="fn">Jani Nikula</span></a>
</span></b>
<pre>(In reply to Rafael Ristovski from <a href="show_bug.cgi?id=100755#c17">comment #17</a>)
<span class="quote">> You can see a clear difference:</span >
Yeah. The link M and N values are used to regenerate the pixel clock from the
link clock on the sink side. Regenrated pixel clock = M / N * link clock. They
are 24 bit values, and per the DP spec the source can choose them freely, as
long as they are within the error boundaries described in <a href="show_bug.cgi?id=100755#c12">comment #12</a>.
Except now we have sinks that fail on some values, and some other sinks that
fail on some other values. I am not amused.
Pixel clock 69300:
<span class="quote">> Good:
> [1.710939] [drm:intel_dump_pipe_config] dp m_n: lanes: 2; gmch_m: 2422210,
> gmch_n: 8388608, link_m: 134567, link_n: 524288, tu: 64</span >
Regenerated pixel clock 69299.869537354. We don't know whether the sink rounds
that to 69299 or 69300.
<span class="quote">> Bad:
> [1.708518] [drm:intel_dump_pipe_config] dp m_n: lanes: 2; gmch_m: 302776,
> gmch_n: 1048576, link_m: 33642, link_n: 131072, tu: 64</span >
Regenerated pixel clock with the rounding patch 69300.384521484 and without the
rounding patch 69298.324584961. They should be rounded to 69300 and 69298,
respectively.
I don't see a whole lot of difference here. Except that the sinks don't know
how to count.</pre>
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