I can still confirm this bug with Linux 4.6.0. :(

Audio support requires DAL which is not upstream yet.  E.g.,
https://cgit.freedesktop.org/~agd5f/linux/log/?h=drm-next-4.7-wip-dal

At least something to await for! Would be neat to put this info somewhere in a non-dev press release. I fiddled many hours with this issue without knowing anything about the state of HDMI audio on AMDGPU. There must be countless frustrated users, even more when you think of the Ubuntu 16.04 shift away from fglrx.

JFYI: HDMI audio output works fine with amdgpu as present in current https://cgit.freedesktop.org/~agd5f/linux/log/?h=amd-staging-drm-next

I just got kernel 4.14, but I still don't have any audio output via HDMI. Is that supposed to work by now?

No, it will be merged with Linux 4.15 but you will still need an kernel parameter: https://www.phoronix.com/scan.php?page=news_item&px=AMDGPU-DC-Accepted
Until then, you have to compile yourself a patched kernel. For Arch-based distros you can use the AUR linux-amd-staging-drm-next-git. Phoronix provides pre-compiled packages for Ubuntu.

With 4.15 (and the kernel boot parameter!) I now managed to get audio output via HDMI. 

Splendid!

My configuration is 

PC ----HDMI---> Pioneer AV receiver (vsx330) ---HDMI---> HP monitor (lp2475w)

But there is one bad effect now: When I turn off the monitor during runtime, or if the monitor enters power-save state, and it is turned on again, the screen resolution is reset to a maximum of 1368x768 (before: 1920x1200), which messes up the desktop.

The reason is that when the monitor is turned off, this seems to be sensed as a change in the HMDI connection, and the EDID data is now coming from the AV receiver. 

dmesg says:

[   82.689994] [drm] VSX-330: [Block 0] 
[   82.689995] [drm] VSX-330: [Block 1] 
[   82.689997] [drm] dc_link_detect: manufacturer_id = 2F41, product_id = 1027, serial_number = 1010101, manufacture_week = 0, manufacture_year = 25, display_name = VSX-330, speaker_flag = 79, audio_mode_count = 8
[   82.689998] [drm] dc_link_detect: mode number = 0, format_code = 1, channel_count = 1, sample_rate = 127, sample_size = 7
[   82.689999] [drm] dc_link_detect: mode number = 1, format_code = 1, channel_count = 7, sample_rate = 127, sample_size = 7
[   82.690000] [drm] dc_link_detect: mode number = 2, format_code = 2, channel_count = 5, sample_rate = 7, sample_size = 80
[   82.690000] [drm] dc_link_detect: mode number = 3, format_code = 7, channel_count = 6, sample_rate = 6, sample_size = 192
[   82.690001] [drm] dc_link_detect: mode number = 4, format_code = 9, channel_count = 1, sample_rate = 127, sample_size = 0
[   82.690002] [drm] dc_link_detect: mode number = 5, format_code = 10, channel_count = 7, sample_rate = 6, sample_size = 0
[   82.690002] [drm] dc_link_detect: mode number = 6, format_code = 11, channel_count = 7, sample_rate = 126, sample_size = 1
[   82.690003] [drm] dc_link_detect: mode number = 7, format_code = 12, channel_count = 7, sample_rate = 126, sample_size = 0
[   82.691002] Raw EDID:
[   82.691003]          c8 01 00 00 06 00 00 00 20 00 00 00 02 00 00 00
[   82.691003]          80 07 00 00 b0 04 00 00 01 00 0a 00 fc 05 e0 01
[   82.691004]          e0 04 00 00 00 00 00 00 01 00 01 00 00 00 02 00
[   82.691004]          00 00 00 00 00 0a 00 00 01 00 00 00 70 00 00 00
[   82.691004]          08 00 02 00 fc 05 e0 01 12 00 07 00 fc 05 e0 01
[   82.691005]          9b 01 00 00 04 00 00 00 20 00 00 00 01 00 00 00
[   82.691005]          04 00 00 00 01 00 0a 00 fd 05 e0 01 e0 04 00 00
[   82.691006]          00 00 00 00 1e 00 1e 00 00 00 02 00 00 00 00 00
[   82.691007] amdgpu 0000:01:00.0: HDMI-A-2: EDID invalid.

Note that the monitor is typically labeled as HDMI-A-1.

The screen configuration in KDE lists 1368x768 as the maximum resolution now. 

I managed to restore the old resolution either by rebooting, or by turning off the AV receiver, then turning it back on. Still, the desktop is messed up.

I suspect the receiver manufacturer never validated DPMS.  Most consumer electronic devices (media players, DVD, Bluray, cable boxes, etc.) don't actually blank the display.

Yeah, that is a problem I still have with my AV-setup as well.

In general the fault is caused by the AV receiver not correctly implementing the EDID handling (the timing turning things on/off is usually not correctly validated/implemented).

We could do something like adding an option to re-query the EDID x seconds after an hot plug event and compare if it's changed.

I now believe there is a general problem with amdgpu's new DC. 

On another system, without an AV receiver in the chain, my display resolution is reset to 1368x768 when I turn off the monitor and back on. That's a really mess (not only my desktop after that). I have to reboot to get the full resolution again; killing X or unplugging the monitor does not restore it.

Seems as if I have to turn off DC again and wait for a fix. <grmpf>

I have this issue in my office (RX460) and on my second PC (RX580), reproduceably, all running openSUSE Tumbleweed, 4.15.1.

I feel your pain, I’m experiencing something similar here:
RX 580 → HDMI @ FullHD → Marantz NR1504 → [EDID-Fake-Plug]
RX 580 → DP @ UHD → Dell P2715Q.

Sometimes, when I turn the monitor off and on again, my desktop resolution is reduced to 2048x1536 (this is not even 16:9) and I have no other option than rebooting to get 3840x2160 again. This was new coming with the DC patches but does not happen every time I turn the monitor off and on again, rather rarely, but is endlessly annoying.

Looks like the conversation steered away from audio. 

Please use a new ticket or comment on existing tickets dealing with wrong modes, such as https://bugs.freedesktop.org/show_bug.cgi?id=105046.

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