[Bug 91861] New: [Radeon RS780] Blank screen (no signal) on HDMI after boot in 3.15 & later

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=91861

            Bug ID: 91861
           Summary: [Radeon RS780] Blank screen (no signal) on HDMI after
                    boot in 3.15 & later
           Product: Drivers
           Version: 2.5
    Kernel Version: 3.15 + later
          Hardware: Intel
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: high
          Priority: P1
         Component: Video(DRI - non Intel)
          Assignee: drivers_video-dri@kernel-bugs.osdl.org
          Reporter: michael.selig@fs.com.au
        Regression: No

Created attachment 164451
  --> https://bugzilla.kernel.org/attachment.cgi?id=164451&action=edit
dmesg (kernel 3.18.3) - RS780 blank screen

I use this machine as a HTPC connected to our TV via HDMI. It has been running
Ubuntu of various versions using the RADEON driver with no problems until
Ubuntu 4.10 (kernel 3.16), when this problem first showed itself. I can
successfully boot 3.13 (from Ubuntu 4.04), but when it was announced that VDPAU
was supported on this old Radeon hardware from 3.18, I was hoping that by
upgrading to 3.18, it would not only solve the "blank screen" problem, but also
give me better video performance on XBMC/KODI. Unfortunately 3.18 exhibits the
same "blank screen" problem. I then tried installing other kernel versions
(including 3.19rc5), but nothing from 3.15 onwards works.

The RS780 hardware is integrated on the motherboard, and is fast enough for
videos & TV etc, so I don't really want to change it for a noisy and/or heat
generating video card.

My symptoms are that, after seeing the Grub screen, I see a kernel message or 2
(nothing important) flashing up for a fraction of a second, but then it goes
blank, saying "no signal". I do not see the normal purple Ubuntu splash screen,
which appears before Xorg starts. Interestingly, on occasions it will boot 3.18
successfully, but that is usually after a reboot from 3.13 or 3.14. Once it
boots successfully it seems fairly stable, and I have managed to watch videos
and TV on 3.18 a couple of times though I haven't tested it for long. However
if it is booted again, chances are that it will fail. When the screen is blank,
the system is still up - I can SSH to the box fine. And it seems that Xorg is
up and running fine - Xorg.0.log looks fine - it's just that I can't see
anything!

I have tried radeon.runpm=0 radeon.dpm=0, but they make no difference.

I think this problem may be related to
https://bugzilla.kernel.org/show_bug.cgi?id=83461.

Any ideas?

Thanks,
Mike

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