Re: [PATCH 00/11] Add NVIDIA LSTP USB adapter drivers

[Adrian Ambrozewicz <aambrozewicz@nvidia.com>]

On Tue, Oct 13, 2026 at 01:37:11PM +0200, Greg Kroah-Hartman wrote:
> > Why the auxiliary bus, and why not MFD
> > --------------------------------------
>
> Neither is ok for USB devices, that's not an argument either way.

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