On Sun, 18 Sep 2016, Richard Cochran wrote: > On Fri, Sep 16, 2016 at 10:57:58PM -0400, Nicolas Pitre wrote: > > Subject: [PATCH] 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. > > > > And to make it possible for PTP to be configured out, the select statement > > in the Kconfig entry for those ethernet drivers is changed from selecting > > PTP_1588_CLOCK to PTP_1588_CLOCK_DEFAULT whose purpose is to indicate the > > default Kconfig value for the PTP subsystem. > > > > This way the PTP subsystem may have Kconfig dependencies of its own, such > > as POSIX_TIMERS, without making those ethernet drivers unavailable if > > POSIX timers are cconfigured out. And when support for POSIX timers is > > selected again then PTP clock support will also be selected accordingly. > > > > Drivers must be ready to accept NULL from ptp_clock_register(). > > The pch_gbe driver is a bit special as it relies on extra code in > > drivers/ptp/ptp_pch.c. Therefore we let the make process descend into > > drivers/ptp/ even if PTP_1588_CLOCK is unselected. > > Thanks for the detailed description. > > > diff --git a/drivers/ptp/Kconfig b/drivers/ptp/Kconfig > > index 00e6098e9a..c36c018f0f 100644 > > --- a/drivers/ptp/Kconfig > > +++ b/drivers/ptp/Kconfig > > @@ -4,8 +4,12 @@ > > > > menu "PTP clock support" > > > > +config PTP_1588_CLOCK_DEFAULT > > + tristate > > I see what this option is doing, but I wonder about the name > "DEFAULT". In what sense is this a default?
It provides the default answer for when the PTP_1588_CLOCK config option is available. I could have called it HAVE_PTP_1588_CLOCK or PTP_1588_CLOCK_WANTED but none of the alternatives struck me as any better. Any idea? > > +/** > > + * ptp_clock_register() - register a PTP hardware clock driver > > + * > > + * @info: Structure describing the new clock. > > + * @parent: Pointer to the parent device of the new clock. > > Here we should finally explain the return value for authors of new > drivers. Something like this: > > * Returns a valid pointer on success or PTR_ERR on failure. If PHC > * support is missing at the configuration level, this function > * returns NULL, and drivers are expected to gracefully handle that > * case separately. Good point. Nicolas
