linux-kernel - Re: [PATCH] net: cpts: Condition WARN_ON on PTP_1588

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Date:   Mon, 20 Apr 2020 14:18:19 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Clay McClure <clay@...mons.net>,
        Grygorii Strashko <grygorii.strashko@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Sekhar Nori <nsekhar@...com>,
        Networking <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: cpts: Condition WARN_ON on PTP_1588_CLOCK

On Mon, Apr 20, 2020 at 08:57:05PM +0200, Arnd Bergmann wrote:
> > d1cbfd771ce82 (Nicolas Pitre       2016-11-11 172) #if IS_REACHABLE(CONFIG_PTP_1588_CLOCK)
> > d1cbfd771ce82 (Nicolas Pitre       2016-11-11 173)
> > d1cbfd771ce82 (Nicolas Pitre       2016-11-11 174) /**
> > d1cbfd771ce82 (Nicolas Pitre       2016-11-11 175)  * ptp_clock_register() - register a PTP hardware clock driver
> > d1cbfd771ce82 (Nicolas Pitre       2016-11-11 176)  *
> > d1cbfd771ce82 (Nicolas Pitre       2016-11-11 177)  * @info:   Structure describing the new clock.
> > d1cbfd771ce82 (Nicolas Pitre       2016-11-11 178)  * @parent: Pointer to the parent device of the new clock.
> > d1cbfd771ce82 (Nicolas Pitre       2016-11-11 179)  *
> > d1cbfd771ce82 (Nicolas Pitre       2016-11-11 180)  * Returns a valid pointer on success or PTR_ERR on failure.  If PHC
> > d1cbfd771ce82 (Nicolas Pitre       2016-11-11 181)  * support is missing at the configuration level, this function
> > d1cbfd771ce82 (Nicolas Pitre       2016-11-11 182)  * returns NULL, and drivers are expected to gracefully handle that
> > d1cbfd771ce82 (Nicolas Pitre       2016-11-11 183)  * case separately.
> > d1cbfd771ce82 (Nicolas Pitre       2016-11-11 184)  */
> 
> The key here is "gracefully". The second patch from Clay just turns NULL into
>  -EOPNOTSUPP and treats the compile-time condition into a runtime error.

You are talking about the cpts driver, no?

I'm worried about ptp_clock_register(), because it does return NULL if
IS_REACHABLE(CONFIG_PTP_1588_CLOCK), and this is the "correct"
behavior ever since November 2016.

If somebody wants to change that stub to return EOPNOTSUPP, then fine,
but please have them audit the callers and submit a patch series.

Thanks,
Richard