linux-kernel - RE: [EXT] Re: [PATCH 0/4] soc: Add support for Marvell OcteonTX2 SDP block

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Date:   Thu, 10 Feb 2022 22:54:39 +0000
From:   Radha Chintakuntla <radhac@...vell.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Satananda Burla <sburla@...vell.com>
Subject: RE: [EXT] Re: [PATCH 0/4] soc: Add support for Marvell OcteonTX2 SDP
 block



> -----Original Message-----
> From: Arnd Bergmann <arnd@...db.de>
> Sent: Thursday, February 10, 2022 8:30 AM
> To: Radha Chintakuntla <radhac@...vell.com>
> Cc: Linux ARM <linux-arm-kernel@...ts.infradead.org>; Arnd Bergmann
> <arnd@...db.de>; Linus Walleij <linus.walleij@...aro.org>; Linux Kernel
> Mailing List <linux-kernel@...r.kernel.org>; Satananda Burla
> <sburla@...vell.com>
> Subject: [EXT] Re: [PATCH 0/4] soc: Add support for Marvell OcteonTX2 SDP
> block
> 
> External Email
> 
> ----------------------------------------------------------------------
> On Wed, Feb 9, 2022 at 11:42 PM Radha Mohan Chintakuntla
> <radhac@...vell.com> wrote:
> >
> > The Marvell OcteonTX2's SDP block is a interface for sending and
> > receiving ethernet packets over the PCIe interface when OcteonTX2 is
> > in PCIe endpoint mode. It interfaces with the OcteonTX2's NIX block
> queues.
> 
> Hi Radha,
> 
> I'm not sure drivers/soc/ is the right place for it. I have not done an actual
> review so far, but I have some high-level questions to clarify how this fits in:
> 
> When you say it is meant for passing ethernet packets, why is it not an
> ethernet driver?

The SDP block sits in between the PCI Endpoint controller and the Network block (NIX). It does an implicit DMA from a remote host to Octeon and has queues to direct to the NIX queues. The host side will have a netdev driver which sends/receives packets on the SDP queues so they make it to the NIX. 
SDP driver doesn't do any packet transmit or receive by itself so that's why it is not a netdev driver. 

> 
> If this drives the PCIe endpoint mode, how does it interface with the pci
> endpoint framework? It looks like a normal PCI driver.
The block does not drive the endpoint mode as such. The driver is just settings up the connection between SDP and NIX. It doesn't touch any of the endpoint registers or setup the endpoint connection. Most of that is done by firmware which detects the mode and sets up the EP controller. 
> 
> What hardware does this run on? Is this only usable when both the host side
> and the endpoint side are Octexon TX2 machines with their packet engines,
> or can one of the two be a different machine that has PCIe host or endpoint
> device support?
It runs on Marvell OcteonTX2 when is in PCIe Endpoint. But the host can be anything - we have tested on x86 and arm64 hosts so far.
The host side will have a netdev driver that will go into the drivers/net area.
> 
>           Arnd