On Tue, 20 Sep 2016, Thomas Gleixner wrote:

> I think the whole approach is wrong because it makes the PTP split at the
> wrong level.
> Currently we have:
>         DRIVER_X
>         tristate "Driver X"
>         select PTP
> In order to make POSIX_CLOCK configurable we should have
>                 PTP
>         tristate "PTP"
>         select POSIX_CLOCK
> Now if you want to distangle PTP from a driver then you split it at the
> driver level and not at the PTP level:
>                 DRIVER_X
>         tristate "Driver X"
>         DRIVER_X_PTP
>         bool "Enable PTP support"
>         default y if !MAKE_IT_TINY
>         depends on DRIVER_X
>         select PTP
> We have already drivers following that scheme. That way you make the PTP
> support in the driver conditional on DRIVER_X_PTP and have no hassle with
> modules and dependencies.

I beg to disagree.

There are way more drivers than subsystems and if you had to go around 
unselecting all NIC drivers for CONFIG_ETHERNET to be turned off, and 
with CONFIG_ETHERNET=n you'd finally be able to turn networking off, 
then this would be a nightmare.

IMHO it is much nicer for the poor user configuring the kernel to have a 
single configuration prompt for PTP support, and then have whatever 
driver that can provide a PTP clock just do it (or omit it) based on 
that single prompt.  Prompting for PTP support for each individual 
ethernet driver is silly.


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