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<b><a class="bz_bug_link
bz_status_REOPENED "
title="REOPENED - [SKL,IVB] HDMI and DP: EDID-supplied BPP is not always properly clamped."
href="https://bugs.freedesktop.org/show_bug.cgi?id=99250#c4">Comment # 4</a>
on <a class="bz_bug_link
bz_status_REOPENED "
title="REOPENED - [SKL,IVB] HDMI and DP: EDID-supplied BPP is not always properly clamped."
href="https://bugs.freedesktop.org/show_bug.cgi?id=99250">bug 99250</a>
from <span class="vcard"><a class="email" href="mailto:sielicki@yandex.com" title="Nicholas Sielicki <sielicki@yandex.com>"> <span class="fn">Nicholas Sielicki</span></a>
</span></b>
<pre>(In reply to Ville Syrjala from <a href="show_bug.cgi?id=99250#c3">comment #3</a>)
<span class="quote">> Let's not be so hasty closing this one. Real world trumps any spec, so I
> think we should make i915 handle this case more gracefully.
>
> I think what we want to do is explicitly check for the DC_36bit thing. I've
> even written that exact patch once but decided not to send it out since I'd
> not seen any monitor that would violate the spec in this manner.</span >
Any problems with this patch? It isn't specific for i915. Tested on the
ivybridge laptop, does what it's supposed to.
There's already a check for this EDID inconsistency in drm_edid.c, but it only
results in a warning. This patch just moves that check up and returns before
setting anything if the EDID is bad, resulting in 8BPC.
Looking at a quick `grep -r HDMI_DC drivers/gpu/drm`, I have a hunch that if I
plugged this monitor into an AMD card, that they would actually be able to
successfully send it 10BPC, and this patch would make them fall back to 8BPC.
So I can understand if you'd want to move this fix into i915/ instead of here.
That being said, depending on how you/they interpret the spec, falling back to
8BPC when the monitor doesn't send DC_36 might technically be more correct,
anyway.
Thanks again for the help.</pre>
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