Re: [PATCH] net: cpts: Condition WARN_ON on PTP_1588_CLOCK

[Grygorii Strashko]

Hi

On 21/04/2020 00:42, Arnd Bergmann wrote:
> On Mon, Apr 20, 2020 at 11:34 PM Richard Cochran
> <richardcochran@xxxxxxxxx> wrote:
> > On Mon, Apr 20, 2020 at 11:21:20PM +0200, Arnd Bergmann wrote:
> > > It's not great, but we have other interfaces like this that can return NULL for
> > > success when the subsystem is disabled. The problem is when there is
> > > a mismatch between the caller treating NULL as failure when it is meant to
> > > be "successful lack of object returned".
> >
> > Yeah, that should be fixed.
> >
> > To be clear, do you all see a need to change the stubbed version of
> > ptp_clock_register() or not?
>
> No, if the NULL return is only meant to mean "nothing wrong, keep going
> wihtout an object", that's fine with me. It does occasionally confuse driver
> writers (as seen here), so it's not a great interface, but there is no general
> solution to make it better.

As per commit
commit d1cbfd771ce8297fa11e89f315392de6056a2181
Author: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>
Date:   Fri Nov 11 00:10:07 2016 -0500

    ptp_clock: Allow for it to be optional
    
    In order to break the hard dependency between the PTP clock subsystem and
    ethernet drivers capable of being clock providers, this patch provides
    simple PTP stub functions to allow linkage of those drivers into the
    kernel even when the PTP subsystem is configured out. Drivers must be
    ready to accept NULL from ptp_clock_register() in that case.
    
    And to make it possible for PTP to be configured out, the select statement
    in those driver's Kconfig menu entries is converted to the new "imply"
    statement. This way the PTP subsystem may have Kconfig dependencies of
    its own, such as POSIX_TIMERS, without having to make those ethernet
    drivers unavailable if POSIX timers are cconfigured out. And when support
    for POSIX timers is selected again then the default config option for PTP
    clock support will automatically be adjusted accordingly.


the idea of using "imply" is to keep networking enabled even if PTP is configured out
and this exactly what happens with cpts driver.
Another question is that CPTS completely nonfunctional in this case and it was never
expected that somebody will even try to use/run such configuration (except for random build purposes).


--
Best regards,
grygorii