[Bug 212449] New: DDC requires amdgpu.dc=0, HDMI sound requires amdgpu.dc=1. Make them work together!

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=212449

            Bug ID: 212449
           Summary: DDC requires amdgpu.dc=0, HDMI sound requires
                    amdgpu.dc=1. Make them work together!
           Product: Drivers
           Version: 2.5
    Kernel Version: 5.4.107
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - non Intel)
          Assignee: drivers_video-dri at kernel-bugs.osdl.org
          Reporter: sdiconov at mail.ru
        Regression: No

I need both DDC and HDMI audio functionality of my radeon RX card, but the
amdgpu kernel driver fails to support both at the same time. I can either use
DDC with 

"amdgpu.hw_i2c=0 amdgpu.dc=0"

OR HDMI audio  with

"amdgpu.dc=1".


The  "dc=1"  kernel switch disables DDC and "dc=0" disables HDMI audio. The
"dcfeaturemask" option might need a new flag to selectively allow i2c
communication with the display while still allowing audio to work over HDMI.




___Details___

I run a radeon RX card supported by the amdgpu module

"# lspci
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI]
Baffin [Radeon RX 550 640SP / RX 560/560X] (rev cf)
01:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Baffin HDMI/DP
Audio [Radeon RX 550 640SP / RX 560/560X]"

It has 1 DP, 1 DVI and 1 HDMI outs.


The GPU is connected to: 1) a Dell U3011 display via DVI (only 2560x1600 video)
and 2) an audio receiver via HDMI (only audio).
The display is shared with another computer, which takes up the display's DP
port. The receiver does not support 2K/4K video resolution and serves as a hifi
DAC+amplifier only. HDMI is the only way to pass digtal PCM 5.1 audio.  

I need DDC to switch video inputs of the Dell U3011 display, because its sensor
buttons and on-screen menus are a real pain to use. gddccontrol is a handy
linux gui app to do it, but it needs i2c and ddc support (which get disabled by
the dc=1 switch).

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