Dmaengine support on aarch64/a64fx?

Rocky Linux General
1

I have aarch64 on Fujitsu ARM64FX (ARMv8) and /sys/class/dma/ channel device symlinks are not populating. A wade through google turns up no release history, supported platform matrix, etc. I’ve used it for custom drivers on gen-3 Pi boards but no later and have no experience with it after ~2016. HPE and Fujitsu are unresponsive and their docs (Hamura, FX7x, and Apollo80 H6220) don’t mention it at all. Anybody here have either the HPE Apollo80 ARM64FX (ARMv8) platform, or any ARMv8 platform, with working DMA Engine channel devices through /sys/class?

Edit: fwiw I’m in the process of getting a test window for a hand-built kernel based on the current production one’s version and config (4.18.0-425.13.1.el8_7.aarch64) but with the verbose debugging on and dmatest builtin instead of modular, and same with the base 4.18.20 kernel because reasons.

2

The Ookami HPC asset at Stonebrook has the same lack of populated DMA channel support and thus lack of DMA Engine support, and thus lack of KNEM support in DMA mode. The assumed answer, lacking response from Fujitsu or HPE, is that native a64fx does not support native DMA channels. That said, XPMEM does appear to be slightly better than KNEM on A64FX given a reasonable range of message sizes, so we’re keeping KNEM around for comparison of the non-DMA userspace with XPMEM.