linux-kernel - RE: [PATCH v7 15/18] NTB: Add support for EPF PCI-Express Non-Transparent Bridge

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Date:   Wed, 11 Nov 2020 02:49:51 +0000
From:   Sherry Sun <sherry.sun@....com>
To:     Kishon Vijay Abraham I <kishon@...com>,
        Arnd Bergmann <arnd@...nel.org>
CC:     "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "arnd@...db.de" <arnd@...db.de>,
        "jdmason@...zu.us" <jdmason@...zu.us>,
        "dave.jiang@...el.com" <dave.jiang@...el.com>,
        "allenbh@...il.com" <allenbh@...il.com>,
        "tjoseph@...ence.com" <tjoseph@...ence.com>,
        Rob Herring <robh@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-ntb@...glegroups.com" <linux-ntb@...glegroups.com>
Subject: RE: [PATCH v7 15/18] NTB: Add support for EPF PCI-Express
 Non-Transparent Bridge

Hi Kishon,

> Subject: Re: [PATCH v7 15/18] NTB: Add support for EPF PCI-Express Non-
> Transparent Bridge
> 
> Hi Sherry, Arnd,
> 
> On 10/11/20 8:29 pm, Arnd Bergmann wrote:
> > On Tue, Nov 10, 2020 at 3:20 PM Kishon Vijay Abraham I <kishon@...com>
> wrote:
> >> On 10/11/20 7:55 am, Sherry Sun wrote:
> >
> >>> But for VOP, only two boards are needed(one board as host and one
> >>> board as card) to realize the communication between the two systems,
> so my question is what are the advantages of using NTB?
> >>
> >> NTB is a bridge that facilitates communication between two different
> >> systems. So it by itself will not be source or sink of any data
> >> unlike a normal EP to RP system (or the VOP) which will be source or sink
> of data.
> >>
> >>> Because I think the architecture of NTB seems more complicated. Many
> thanks!
> >>
> >> yeah, I think it enables a different use case all together. Consider
> >> you have two x86 HOST PCs (having RP) and they have to be communicate
> >> using PCIe. NTB can be used in such cases for the two x86 PCs to
> >> communicate with each other over PCIe, which wouldn't be possible
> without NTB.
> >
> > I think for VOP, we should have an abstraction that can work on either
> > NTB or directly on the endpoint framework but provide an interface
> > that then lets you create logical devices the same way.
> >
> > Doing VOP based on NTB plus the new NTB_EPF driver would also work and
> > just move the abstraction somewhere else, but I guess it would
> > complicate setting it up for those users that only care about the
> > simpler endpoint case.
> 
> I'm not sure if you've got a chance to look at [1], where I added support for
> RP<->EP system both running Linux, with EP configured using Linux EP
> framework (as well as HOST ports connected to NTB switch, patches 20 and
> 21, that uses the Linux NTB framework) to communicate using virtio over
> PCIe.
> 

I saw your patches at [1], here you take a rpmsg as an example to communicate between
two SoCs using PCIe RC<->EP and HOST1-NTB-HOST2 for different usercases.
The VOP code works under the PCIe RC<->EP framework, which means that we can also
make VOP works under the Linux NTB framework, just like the rpmsg way you did here, right?

Best regards
Sherry

> The cover-letter [1] shows a picture of the two use cases supported in that
> series.
> 
> [1] ->
> https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Flore.ke
> rnel.org%2Fr%2F20200702082143.25259-1-
> kishon%40ti.com&amp;data=04%7C01%7Csherry.sun%40nxp.com%7C5d8b7
> 3a4b72947bea65d08d8858f5091%7C686ea1d3bc2b4c6fa92cd99c5c301635%7
> C0%7C0%7C637406197865119992%7CUnknown%7CTWFpbGZsb3d8eyJWIjoi
> MC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C100
> 0&amp;sdata=iRrBvQ9xjoOUYU%2FDidMLZZpW6XuU4ITVXFDA%2B%2F4rJFU
> %3D&amp;reserved=0
> 
> Thank You,
> Kishon