linux-kernel - Re: [PATCH RFC 1/5] kconfig: implement weak reverse-dependencies

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Message-ID: <20130321114307.GA6716@netboy.at.omicron.at>
Date:	Thu, 21 Mar 2013 12:43:08 +0100
From:	Richard Cochran <richardcochran@...il.com>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	Michal Marek <mmarek@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
	Tejun Heo <tj@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	netdev@...r.kernel.org
Subject: Re: [PATCH RFC 1/5] kconfig: implement weak reverse-dependencies

On Thu, Mar 21, 2013 at 03:06:11PM +0400, Konstantin Khlebnikov wrote:
> 
> As I see this technology requires special dedicated server in the local
> network, thus it's unusable in most situations. But it starts working
> without any actions from the user (please fix me if I'm wrong).

Perhaps you don't have a very clear picture of how this PTP stuff
works. Even when the PHC and time stamping code is compiled in, it
does *not* start working unless the end user turns it on, via the
SIOCSHWTSTAMP and SO_TIMESTAMPING options.

See: Documentation/networking/timestamping.txt
     Documentation/ptp/ptp.txt

> Thus this code enables some rarely used parts of hardware.
> After seeing several weird bugs in ethernet devices I prefer to
> keep unused/unwanted features off.

Just compiling drivers into kernel does not really change the behavior
of the hardware. The only drawback I know of is that it adds (minimal)
overhead into the packet processing paths, but that is a software
issue.

I don't mean to start a big discussion here. The question of whether
to have PHC support a compile time option should be discussed on the
netdev list (added on CC just in case).

Thanks,
Richard

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