AMD Linux Graphics Driver Preparing For Enabling New LSDMA Ring Mode

Going back to May 2022, AMD Linux graphics driver engineers were working on AMDGPU driver patches to enable a new Light System DMA "LSDMA" IP block. Since then we haven't heard much about LSDMA until some new patches surfaced yesterday for optionally enabling the LSDMA ring mode for the AMDGPU kernel driver.

LSDMA is a new hardware block that can be utilized for paging and system buffer management. In turn this can lead to power savings and more efficient use over existing SDMA capabilities on Radeon GPUs when leveraging the LSDMA ring mode. The 8 new patches posted on Wednesday describe the LSDMA ring mode as:

"This series implements LSDMA ring mode, creates LSDMA ring and implement amdgpu ring related functions. Introduce a new module parameter amdgpu_lsdma to enable LSDMA, switch buffer and paging funcs from SDMA to LSDMA. It changes amdgpu driver buffer operations to LSDMA, changes default page table update to LSDMA. Since LSDMA is outside GFX domain, it can work without waking up GFX which saves power in mutiple scenarios. With LSDMA dedicated ring create, it also exposes interfaces for users to utilize LSDMA capabilies. This series is tested on gfx 11.0.4."

These LSDMA capabilities are found with GFX11 (RDNA3) hardware. Until the LSDMA ring mode proves itself stable for the AMDGPU Linux kernel driver, it's disabled by default and will require users set the amdgpu.lsdma=1 module parameter for enabling.

If all goes well this LSDMA support could land in the Linux 6.8 kernel that will be out in the early months of 2024. Better late than never.