Mellanox is a supplier of InfiniBand and Ethernet products for servers and storage. Mellanox products are widely-used in the high-end HPC market and data centers.
The x86/platform code enables support for Mellanox Technologies platforms with support for hardware like their MSX6710, MSX8720, MSB7700, MSN2700, MSX1410, MSN2410, MSB7800, MSN2740, and MSN2100, among other products. This MLX_PLATFORM support was developed by Mellanox engineers and is now being mainlined in the Linux kernel after going through several rounds of revisions.
It's great to see more companies working towards mainline kernel support. You probably won't find any of the hardware though in your closet or any bargain bins with the MSX6710 36-port switch costing $11.9k USD, the MSN2100 100GbE Open Ethernet Switch retailing for over $10k USD, etc.
More details via the x86/platform pull request that also has SGI UV x86 and Intel MID updates.