netdev - Re: [PATCH 4/4] thunderbolt: Get rid of E2E workaround

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Message-ID: <CA+CmpXst-5i4L5nW-Z66ZmxuLhdihjeNkHU1JdzTwow1rNH7Ng@mail.gmail.com>
Date:   Mon, 15 Jun 2020 17:18:38 +0300
From:   Yehezkel Bernat <yehezkelshb@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-usb@...r.kernel.org, Michael Jamet <michael.jamet@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Andreas Noever <andreas.noever@...il.com>,
        Lukas Wunner <lukas@...ner.de>, netdev@...r.kernel.org
Subject: Re: [PATCH 4/4] thunderbolt: Get rid of E2E workaround

On Mon, Jun 15, 2020 at 4:51 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Mon, Jun 15, 2020 at 04:45:22PM +0300, Yehezkel Bernat wrote:
> > On Mon, Jun 15, 2020 at 4:02 PM Mika Westerberg
> > <mika.westerberg@...ux.intel.com> wrote:
> > >
> > > diff --git a/include/linux/thunderbolt.h b/include/linux/thunderbolt.h
> > > index ff397c0d5c07..5db2b11ab085 100644
> > > --- a/include/linux/thunderbolt.h
> > > +++ b/include/linux/thunderbolt.h
> > > @@ -504,8 +504,6 @@ struct tb_ring {
> > >  #define RING_FLAG_NO_SUSPEND   BIT(0)
> > >  /* Configure the ring to be in frame mode */
> > >  #define RING_FLAG_FRAME                BIT(1)
> > > -/* Enable end-to-end flow control */
> > > -#define RING_FLAG_E2E          BIT(2)
> > >
> >
> > Isn't it better to keep it (or mark it as reserved) so it'll not cause
> > compatibility issues with older versions of the driver or with Windows?
>
>
> How can you have "older versions of the driver"?  All drivers are in the
> kernel tree at the same time, you can't ever mix-and-match drivers and
> kernels.
>
> And how does Windows come into play here?
>

As much as I remember, this flag is sent as part of creating the
interdomain connection.
If we reuse this bit to something else, and the other host runs an
older kernel or
Windows, this seems to be an issue.
But maybe I don't remember it correctly.