netdev - Re: [PATCH net-next v2] ethernet/intel: fix PTP_1588

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Date:   Mon, 2 Aug 2021 22:32:08 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     "Keller, Jacob E" <jacob.e.keller@...el.com>
Cc:     Richard Cochran <richardcochran@...il.com>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        "Saleem, Shiraz" <shiraz.saleem@...el.com>,
        "Ertman, David M" <david.m.ertman@...el.com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v2] ethernet/intel: fix PTP_1588_CLOCK dependencies

On Mon, Aug 2, 2021 at 9:54 PM Keller, Jacob E <jacob.e.keller@...el.com> wrote:
>
> So go back to "select"?
>
> It looks like Arnd proposed in the thread a solution that did a sort of
> "please enable this" but still let you disable it.
>
> An alternative (unfortunately per-driver...) solution was to setup the
> drivers so that they gracefully fall back to disabling PTP if the PTP
> core support is not reachable.. but that obviously requires that drivers
> do the right thing, and at least Intel drivers have not tested this
> properly.
>
> I'm definitely in favor of removing "implies" entirely. The semantics
> are unclear, and the fact that it doesn't handle the case of "i'm
> builtin, so my implies can't be modules"...
>
> I don't really like the syntax of the double "depends on A || !A".. I'd
> prefer if we had some keyword for this, since it would be more obvious
> and not run against the standard logic (A || !A is a tautology!)

I think the main reason we don't have a keyword for it is that nobody
so far has come up with an English word that expresses what it is
supposed to mean.

You can do something like it for a particular symbol though, such as

config MAY_USE_PTP_1588_CLOCK
       def_tristate PTP_1588_CLOCK || !PTP_1588_CLOCK

 config E1000E
        tristate "Intel(R) PRO/1000 PCI-Express Gigabit Ethernet support"
        depends on PCI && (!SPARC32 || BROKEN)
+       depends on MAY_USE_PTP_1588_CLOCK
        select CRC32
-       imply PTP_1588_CLOCK


          Arnd