netdev - Re: [PATCH net-next 2/5] dt-bindings: net: Add tsnep Ethernet controller

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Date:   Thu, 29 Jul 2021 09:07:06 +0200
From:   Gerhard Engleder <gerhard@...leder-embedded.com>
To:     Michal Simek <michal.simek@...inx.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>, devicetree@...r.kernel.org
Subject: Re: [PATCH net-next 2/5] dt-bindings: net: Add tsnep Ethernet controller

On Thu, Jul 29, 2021 at 7:07 AM Michal Simek <michal.simek@...inx.com> wrote:
> On 7/28/21 10:14 PM, Gerhard Engleder wrote:
> > On Wed, Jul 28, 2021 at 12:55 PM Michal Simek <michal.simek@...inx.com> wrote:
> >>>>>>>> +      - enum:
> >>>>>>>> +        - engleder,tsnep
> >>>>>>>
> >>>>>>> tsnep is pretty generic. Only 1 version ever? Or differences are/will
> >>>>>>> be discoverable by other means.
> >>>>>>
> >>>>>> Differences shall be detected by flags in the registers; e.g., a flag for
> >>>>>> gate control support. Anyway a version may make sense. Can you
> >>>>>> point to a good reference binding with versions? I did not find a
> >>>>>> network controller binding with versions.
> >>>>>
> >>>>> Some of the SiFive IP blocks have versions. Version numbers are the
> >>>>> exception though. Ideally they would correspond to some version of
> >>>>> your FPGA image. I just don't want to see 'v1' because that sounds
> >>>>> made up. The above string can mean 'v1' or whatever version you want.
> >>>>> I'm fine if you just add some description here about feature flag
> >>>>> registers.
> >>>>
> >>>> Don't Xilinx design tool (vivado) force you to use IP version?
> >>>> Normally all Xilinx IPs have certain version because that's the only way
> >>>> how to manage it.
> >>>
> >>> Yes I use an IP version in the Xilinx design tool. I use it as a version of the
> >>> VHDL code itself. In my case this version is not related to the
> >>> hardware software
> >>> interface. The goal is to keep the hardware software interface compatible, so
> >>> the IP version should not be relevant.
> >>
> >> I expect this is goal for everybody but it fails over time. We normally
> >> compose compatible string for PL based IP with IP version which is used.
> >> And it is quite common that couple of HW version are SW compatible to
> >> each other.
> >> It means use the same HW version as you use now. When you reach the
> >> point when your HW IP needs to be upgraded and will require SW alignment
> >> you have versions around which can be used directly.
> >
> > I would like to follow the argument from Rob:
> > "The above string can mean 'v1' or whatever version you want."
> > If there ever is an incompatible new IP version, then a new compatible string
> > can be added which means 'v2'. E.g. for 128bit physical address support I
> > would choose the compatible string 'engleder,tsnep128'. I don't see an
> > advantage in adding a version number to the compatible string.
> >
> > This IP will be used in products where compatible hardware is a must.
> > An IP upgrade which requires SW alignment will result in heavy complaints
> > from the customers. Such an IP upgrade would result in a new IP.
> > Like for shared libraries, an incompatible API change is similar to a new
> > library.
>
> From my point of view where I expect the most of customers are using
> Xilinx DTG (device tree generator) compatible string is composed with IP
> name and version used in design tool. This is unique combination which
> properly describes your HW.
> And choosing different compatible string or string without version is
> breaking this connection between hw design tool and sw.
>
> From my perspective it is much simpler to understand that your HW ip
> called ABC-rev1 requires DT node which is your_company,ABC-rev1 instead
> of any made name.
> But up2you - you will be talking to your customers.

Thanks for explaining your point of view. From my side I don't expect that
Xilinx DTG is used. The few people I know who are working with Zynq/ZynqMP
are using the Xilinx tools only to generate the bitstream. This way you are able
to do software development for the Zynq/ZynqMP like for any other hardware
platform.

Thanks for your Feedback!

Gerhard