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@kernel-bugs.osdl.org Reporter: sdiconov@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).