Re: [PATCH net-next 0/5] net/mlx5: Introduce mlx5_nodnic, a driver for DRAM-less NVIDIA Mellanox NIC functions

[Simon Horman <horms@kernel.org>]

On Wed, Sep 30, 2026 at 03:57:03PM +0300, Tariq Toukan wrote:
> Hi,
> 
> This series by Shahar introduces mlx5_nodnic, a Linux driver for the
> NODNIC (No-DRAM NIC) hardware interface present in Mellanox/NVIDIA
> ConnectX-family ASICs since 2015.
> 
> NODNIC is a first-class hardware capability.
> It defines a lightweight NIC function intended for contexts where local
> DRAM is unavailable or too costly: embedded controllers, management
> planes, pre-boot environments, or any resource-constrained instantiation
> of a ConnectX NIC. The hardware sends and receives ordinary Ethernet
> frames via SQs, RQs and CQs. There is no encapsulation, no private
> protocol, and no FW interposition: packets are forwarded as standard
> Ethernet between whatever peers are connected to the function. The
> interface is documented in the HW spec and has been in production in
> non-Linux OS drivers for over a decade.
> 
> Where it is used today:
> - Embedded management controllers on ConnectX-class ASICs that need a
>   network path to the host without consuming a data-path PF.
> - Resource-constrained SoC integrations (no local DRAM) where a
>   minimal-footprint driver is required.
> - Pre-boot / early-OS environments (PXE, iSCSI boot) that need a NIC
>   without a full mlx5e stack.
> - BF4 management PFs (one concrete deployment): on BlueField-4 the
>   firmware exposes a NODNIC PF on the host side and a peer PF on the ARM
>   side, using standard vport forwarding to connect them. This provides
>   in-band Ethernet connectivity between the host and the DPU OS - SSH,
>   PXE, and any standard networking application work over it without any
>   special handling.
> 
> Design notes:
> - The driver is separate from mlx5e rather than a mode within it.
>   NODNIC uses PCI Vendor Specific Capability (VSC) for command
>   operations - reads and writes over PCI config space - instead of the
>   DMA-based command interface used by mlx5_core. This is what makes
>   NODNIC usable in environments without reliable DMA access, and it
>   makes the two command paths fundamentally incompatible. Folding this
>   into mlx5e would mean carrying a second command transport and a second
>   resource model through code that is already dense.
> - A single SQ, RQ and shared CQ are exposed per function, with two MSI-X
>   vectors: the data vector fires on CQEs and drives both TX and RX
>   completions, and the event vector notifies on port state changes.
>   This is the hardware's model, not a driver simplification.
> - The driver exposes a plain netdev with no private uAPI, no ioctls and
>   no vendor-specific configuration surface. Everything is driven through
>   standard netdev, ethtool and devlink interfaces.
> - The code lives under drivers/net/ethernet/mellanox/mlx5/nodnic/ and
>   shares no paths with mlx5e, keeping the footprint small and the blast
>   radius of changes contained.

Thanks for the above. I agree that this is a valid use-case.
And that the design approach taken is appropriate.

One minor nit: the above mentions devlink, but that doesn't seem to
appear in the driver. Not a big deal. But something I noticed.

Also, I do note that the first two patches are rather large.
But it's a new driver, and that is hard to avoid.

...