Efficiently training memory device chip select control

A chip select training mode (CSTM) enables a memory subsystem to train a chip select signal separately from command bus training. A memory device and a memory controller can connect via a command bus including a chip select signal line. Instead of training the chip select along with other signal lines of the command bus, a CSTM mode enables the memory subsystem to more accurately train the chip select. The memory device can be triggered for CSTM mode with a command, and then train voltage margining for the CS signal line to align chip select signaling with the memory subsystem clock signal.