DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=date:from:to:cc:subject:message-id:references:mime-version
         :content-type:content-disposition:in-reply-to:user-agent;
        b=c/58410ySrjufUn758bzS2QbYw+2DnLAbdbTd0NctcXRQsqv6kOPm15mHMIdmRy9F/
         493oSGzyLqEWO0LbVjLyCaI2FbEsYOh8LcWsPHH9LKZOqp6iF26sAFJ52wzubLjzD0RL
         ypN9tYCEr4YwPoU0VXzuYT71kuECivKjCLEmU=
Date: Tue, 17 Aug 2010 10:32:16 +0200
From: Richard Cochran <richardcochran@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: linuxppc-dev@lists.ozlabs.org, Rodolfo Giometti <giometti@linux.it>,
        netdev@vger.kernel.org, devicetree-discuss@lists.ozlabs.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        Krzysztof Halasa <khc@pm.waw.pl>
Subject: Re: [PATCH 1/5] ptp: Added a brand new class driver for ptp clocks.
Message-ID: <20100817083216.GA3330@riccoc20.at.omicron.at>
References: <cover.1281956490.git.richard.cochran@omicron.at>
 <201008161626.24083.arnd@arndb.de>
 <20100816190003.GB4166@riccoc20.at.omicron.at>
 <201008162159.39734.arnd@arndb.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <201008162159.39734.arnd@arndb.de>
User-Agent: Mutt/1.5.20 (2009-06-14)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1464
Lines: 36

On Mon, Aug 16, 2010 at 09:59:39PM +0200, Arnd Bergmann wrote:
> Why does it matter how long it takes to read the clock? I wasn't thinking
> of replacing the system clock with this, just exposing the additional
> clock as a new clockid_t value that can be accessed using the existing
> syscalls.

Okay, now I see. You are suggesting this:

      clock_gettime(CLOCK_PTP, &ts);
      clock_settime(CLOCK_PTP, &ts);

I like this. If there is agreement about it, I am happy to implement
the PTP stuff that way.

> Why did you not want to add syscalls? Adding ioctls instead of syscalls
> does not make the interface better, just less visible.

I bet that, had I posted patch set with new syscalls, someone would
have said, "You are adding new syscalls. Can't you just use a char
device instead!"

If you add syscalls and introduce CLOCK_PTP, then you add it to
everyone's kernel, even those people who never heard of PTP. A char
device has the advantage that can it be simply ignored. Also, a
syscall has got to have the right form from the very beginning. If the
next generation of PTP hardware looks very different, then it is not
that much of a crime to change an ioctl interface, provided it has
versioning.

Richard

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/