[Bug 91434] [IVB/HSW] 23.976Hz & 24Hz modes broken on dual-display with recent (4.0.x) kernels

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=91434

--- Comment #35 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to Martin Andersen from comment #34)
> There is no DP-HDMI dongle involved. The output is fed directly from a
> MacBook Retina system via full-size/regular HDMI cable. (Yes, I've also
> noticed it says DP.)

That just means the DP++ chip is likely soldered onto the motherboard. It's
definitely somewhere because it answers when we talk to it.

> 
> However; the exact same setup works 100% correctly with older kernels, as
> outlined earlier in the ticket. By 100% i mean: never any picture dropouts,
> never any dots (which only were seen with this most recent kernel) or other
> graphical glitches.

That's probably because older kernels only did 8bpc, whereas newer ones do
12bpc whenever possible.

> I have three other sources hooked up to this projector, and none have
> issues.

Can you tell whether any of them do 12bpc HDMI output, or just 8bpc?

> The same behaviour is seen when hooked up directly to either of the
> projector's two HDMI ports - with another cable - as well. So I believe
> 'cabling issues' can be ruled out.

The cables aren't unusually long are they?

It's definitely possible that the signal degradation happens either in the
source of sink side. I could almost excuse the source side for not being tested
to handle 12bpc iff Apple's own driver always uses 8bpc and they didn't expect
anyone to install another OS on the thing. If the problem is in the projector
then I think it's less excusable, and they should have tested to make sure the
device works with the maximum TMDS clock it's advertising to the source.

-- 
You are receiving this mail because:
You are the assignee for the bug.
You are on the CC list for the bug.
You are the QA Contact for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/intel-gfx-bugs/attachments/20171011/72afcd44/attachment.html>