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Here USB only carries the traffic. The I2C, SPI and GPIO channels are ordinary controllers on the board, and their drivers register with those subsystems; hosts describe what is wired to them with ACPI, BMCs with device tree [1]. usb-ljca is a recent driver for a very similar device, so we modelled the core on it: one interface carries GPIO, I2C and SPI, and the core creates an auxiliary device per function and attaches its ACPI node. LSTP extends that model to device tree. Whether the next version stays LSTP or becomes a set of divergences from an OBMF-ICP driver, as Jeremy suggested, the need is the same: a device behind a tunnelled channel is described like one wired straight to the BMC, so a board can move between the two without rewriting its description. We don't see an architecture that fits better. If you would rather see this done differently, what would you suggest? One function per interface I'll answer separately. [1] https://lore.kernel.org/r/20261016084443.1972351-1-aambrozewicz@nvidia.com Thanks, Adrian