[Intel-gfx] [REGRESSION] i915: No HDMI output with 4.4

[Oleksandr Natalenko]

Here is full dmesg with verbose patch on 4.4.1 and dual-link DVI-HDMI 
cable: [1]

Dual-link works OK:

===
лют 16 17:46:38 pfactum.lanet kernel: port C live status
                                           
##################################################
                                           
##################################################
                                           
##################################################
                                           
##################################################
                                           
##################################################
===

Also:

===
[~]$ sudo intel_reg read 0xc4000 0xc4004 0xc4008 0xc400c 0xc4030
                                     (0x000c4000): 0x00400000
                                     (0x000c4004): 0xf1b4ffff
                                     (0x000c4008): 0x00000000
                                     (0x000c400c): 0xffffffff
                                     (0x000c4030): 0x00101010
[~]$ sudo intel_reg read 0xc2000 0xc2004 0xc2020
                                     (0x000c2000): 0x00000000
                                     (0x000c2004): 0x00000001
                                     (0x000c2020): 0x60004000
===

Let me know if you need more info.

[1] https://gist.github.com/dfbf237e74ed6e0b1bf7

16.02.2016 14:54, Daniel Vetter wrote:
> On Tue, Feb 16, 2016 at 12:58:56PM +0200, Oleksandr Natalenko wrote:
>> Ville, Daniel,
>> 
>> I've just got another monitor and another DVI-HDMI cable, and here 
>> what I've
>> got.
>> 
>> ===Single Link DVI-D cable with 3 different monitors===
>> 
>> Computer DVI ——— DVI-D (Single Link)/HDMI cable ——— HDMI LG 23MP65HQ-P 
>> ===
>> not working
> 
> I presume the above LG screen is what you've called previously "old
> monitor"?
> 
>> Computer DVI ——— DVI-D (Single Link)/HDMI cable ——— HDMI LG 23MP67HQ-P 
>> ===
>> not working
>> Computer DVI ——— DVI-D (Single Link)/HDMI cable ——— HDMI LG 23MP55HQ-P 
>> ===
>> works!
>> 
>> ===Dual Link DVI-D cable with monitor that doesn't work with Single 
>> Link
>> cable===
>> 
>> Computer DVI ——— DVI-D (Dual Link)/HDMI cable ——— HDMI LG 23MP65HQ-P 
>> ===
>> works!
> 
> Funky. Can you pls grab the debug logs (with the special patches from
> Ville) for this case? I wonder why suddenly different cable and it 
> works.
> 
> Also: Is this one of these older-ish screens where you must have a
> dual-link cable to drive it at full resolution&refresh rate?
> -Daniel
> 
> 
>> ===Laptop with HDMI output===
>> 
>> Laptop HDMI ——— HDMI/HDMI cable ——— HDMI LG 23MP65HQ-P === works!
>> 
>> I'd say that single link DVI cables are broken with new kernel, but 
>> one of
>> monitors could work with such a cable. So I have no idea :(.
>> 
>> Regards,
>>   Oleksandr.
>> 
>> 15.02.2016 17:42, Daniel Vetter wrote:
>> >The other downside is that it'll make us non-compliant, which was the
>> >point of this entire ordeal: HDMI spec forbids us from starting any i2c
>> >transactions when the hpd isn't signalling a present screen.
>> >
>> >So maybe we need to buy one of these broken screens.
>> >
>> >Oleksandr, what exact model are you using? And any chance that you could
>> >test this on some other machine with intel gfx and latest kernel, just to
>> >make sure this really is some issue with the sink and not with the machine
>> >itself? And I guess you've tested with some other hdmi sink, and that
>> >works?