AMDGPU DC Display Code Ported To GCN 1.0 "Southern Islands" GPUs

The AMDGPU DC "Display Code" stack formerly known as DAL that's been in the mainline kernel the past several releases might soon see support for GCN 1.0 "Southern Islands" GPUs. This is the big display code stack necessary for atomic mode-setting, FreeSync/Adaptive-Sync, HDMI/DP audio, and other modern display features. When AMD brought up this DC stack, they hadn't brought it back to GCN 1.0 since for those original GCN GPUs they by default still use the Radeon DRM driver. But now they might soon see AMDGPU DC support.

Mauro Rossi of the Android-x86 team has sent out a set of 13 patches implementing basic AMD DC support for Southern Islands. It's yet to be seen though if AMD developers would be interested in accepting these patches as it would be an additional maintenance burden for an already large and complex piece of the driver that is also shared with their proprietary Windows driver.

Android-x86 developers are working on the DC support in order to get atomic mode-setting in place... While atomic mode-setting might not seem like the most captivating feature to invest all this work into, in the Android space you need atomic in order to get the DRM hardware composer and GBM Gralloc running properly. Those pieces are needed in order to get the Vulkan RADV driver running correctly on Android-x86.

With the conventional Linux desktop, you just need GCN 1.0 booted with AMDGPU DRM for RADV support and not have to worry about atomic, but that's not the case for Android on x86. So there are these 13 patches billed as a proof-of-concept.

The patches do appear to work based on the Android-x86 testing but there is a CONFIG_DRM_AMD_DC_SI Kconfig switch introduced in order to avoid the risk of regression if not wanting to build a kernel with DC for Southern Islands enabled.