AMDGPU Linux Driver Enabling New "LSDMA" Block

As part of the increasing flow of AMD Radeon Linux graphics driver patches coming out ahead of the RDNA3 launch later this year, a new hardware block exposed by the latest patches is "LSDMA".

There has long been the SDMA block with AMD GPUs for System DMA (Direct Memory Access) functionality. Seemingly for next-gen RDNA3 GPUs (though could also be some other particular variants given their new block-by-block enablement approach or even next-gen CDNA) is the "LSDMA" IP as part of SDMA.

LSDMA is for Light SDMA and is a supplemental SDMA block beginning with SDMA 6.x IP. The new patches posted on Thursday indicate the Light SDMA functionality is principally reserved for use by the Radeon kernel graphics driver - AMDGPU DRM in this case.

This dedicated "small" LSDMA hardware is presumably for allowing more efficient DMA for the kernel graphics driver itself and not being bottle-necked or sharing resources with the standard SDMA functionality of the GPU. Just one of the subtle differences to note with these new enablement patches, among many other around VCN4, GFX11, and more that have been hitting the mailing lists for patch review in recent days.

Thursday saw the LSDMA support patches published for the first time and will soon be working their way to the mainline Linux kernel.