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[142.162.112.119]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-89a017add76sm10957346d6.36.2026.03.02.06.04.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Mar 2026 06:04:52 -0800 (PST) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1vx3tE-00000003fZH-0C57; Mon, 02 Mar 2026 10:04:52 -0400 Date: Mon, 2 Mar 2026 10:04:52 -0400 From: Jason Gunthorpe To: Keith Busch Cc: Leon Romanovsky , Saeed Mahameed , Tariq Toukan , Mark Bloch , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , linux-rdma@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Maher Sanalla , Max Gurtovoy Subject: Re: [PATCH rdma-next 0/6] Add support for TLP emulation Message-ID: <20260302140452.GW44359@ziepe.ca> References: <20260225-var-tlp-v1-0-fe14a7ac7731@nvidia.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Feb 27, 2026 at 02:37:05PM -0700, Keith Busch wrote: > On Wed, Feb 25, 2026 at 04:19:30PM +0200, Leon Romanovsky wrote: > > This series adds support for Transaction Layer Packet (TLP) emulation > > response gateway regions, enabling userspace device emulation software > > to write TLP responses directly to lower layers without kernel driver > > involvement. > > > > Currently, the mlx5 driver exposes VirtIO emulation access regions via > > the MLX5_IB_METHOD_VAR_OBJ_ALLOC ioctl. This series extends that > > ioctl to also support allocating TLP response gateway channels for > > PCI device emulation use cases. > > Sorry if this is obvious to people in the know, but could you possibly > give a quick high level description of the use case behind this feature? > I'm just curious what emulation needs are enabled by having access to > this packet level. Thanks! These days the DPU world supports what I think of as "software defined PCI functions". Meaning when the DPU receives a PCIe TLP on its PCI interface it may invoke software generate a response packet for that TLP. At least the Mellanox DPU can route the TLPs to software in many different places: various on-device processors, or on the ARM cores running Linux.. So, for example, using this basic capability you can write some software to have the DPU create a PCI function that conforms to the virtio-net specification. Or NVMe. Or whatever else you dream up. The peculiar thing is that this is all tightly coupled to RDMA. Eg if you want your TLP to trigger a DMA from the PCI function then RDMA QPs and MRs have to be used to execute the DMA. Jason