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

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Message-ID: <CANr-f5y4=1hj-6WFT1HdewU=sich6KgkgmR6-qWimFxQiV5MFQ@mail.gmail.com>
Date:   Wed, 28 Jul 2021 22:14:12 +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 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.

Gerhard