KMS but AMDGPU And Black Screen

[Michael Butash]

I have had lots of issues with video and adapters the past few years,
mostly as I'm forced to use them.  My nvidia 1070 in my desktop has 3x
DP1.2 ports and 1 HDMI2.0.  I have 3 displays, so I use the 3x DP1.2 ports,
and run those through adapters to HDMI2.0 on my Samsung TV's I use for
monitors.  Non-stop chaos ensues during power-down and up every day,
something different, every linux desktop hates it.  Often one display or
another will freak out, and I end up; having to hard disconnect the adapter
(ie, reboot it) to work again or it'll come up stuck in 768x1024 (on a 48"
tv...).

I found HDMI doesn't handle DPMS sort of power-off modes as vga, dvi, dp,
or most methods of displays to handle soft power-off scenarios, ala just
power down displays.  When my laptop powers them down, they remain on with
no signal, which seems to just confuse the video card and adapter that both
freak out.  This seems to have a profound effect on displaya and video
cards that don't realize most displays are now hdmi...

Graphic subsystems are a basketcase these days under linux, mostly because
of these damn adapters, dongles
<https://www.youtube.com/watch?v=-XSC_UG5_kU>, and vendor wars.  Intel,
that wants to sell all the things, including the most useless gpu on the
earth, injects themselves into everything, and always cause me issues as I
can't convince the os to use the (real) nvidia gpu.  Probably the same sort
of issue if an intel gpu is around with AMD.  Last I used an AMD GPU some
4-5 years ago, it was an issue.  Nvidia Prime via Intel is still sketchy af.

Even on a dedicated nvidia gpu in a server-ish xeon system, with
DP-to-whatever adapters I had nothing but issues.  My latest iteration is
my laptop (xps 9560) and a thunderbolt3/usb-c dock with 2x 4k/60hz outputs
via one-piece DP-to-HDMI cables.  I still have quirks, but I've learned to
work around, and now somewhat understand really odd hardware behaviour
enough to reproduce it.  Occasionally I still need to disconnect a display
at the DP-to-HDMI cable I use now, which is again oddly random.

I don't like the adapters, but my 48" TV's I use for displays don't often
come with DP ports native, and using HDMI comes with power management
oddities.  A lot depends on your cabling and even display these days.

-mb


On Wed, Aug 19, 2020 at 1:05 PM Seabass via PLUG-discuss <
plug-discuss at lists.phxlinux.org> wrote:

> No, on the desired monitor, it still black screens.
>
> Works just fine (Even without that parameter) on something that has a
> direct HDMI cable, though. (TV)
>
> > Message: 6
> >Date: Tue, 18 Aug 2020 16:23:47 -0700
> > From: Aaron Jones <retro64xyz at gmail.com>
> > To: plugaz at codezilla.xyz, Main PLUG discussion list
> > <plug-discuss at lists.phxlinux.org>
> >Subject: Re: KMS but AMDGPU And Black Screen
> > Message-ID: <6B7D5942-0F2F-4DAE-A54A-19215718DCF2 at gmail.com>
> > Content-Type: text/plain; charset="utf-8"
> >
> > https://bugzilla.redhat.com/show_bug.cgi?id=1594488
> >
> > Set amdgpu.dc=0 in bios and it will work but without hdmi sound.
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