From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: MIME-Version: 1.0 Sender: johnstul.lkml@gmail.com In-Reply-To: References: <363bd749a38d0b785d8431e591bf54c38db4c2d7.1281956490.git.richard.cochran@omicron.at> Date: Mon, 16 Aug 2010 12:38:06 -0700 Message-ID: Subject: Re: [PATCH 1/5] ptp: Added a brand new class driver for ptp clocks. From: john stultz To: Richard Cochran Content-Type: text/plain; charset=ISO-8859-1 Cc: Rodolfo Giometti , netdev@vger.kernel.org, devicetree-discuss@lists.ozlabs.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, Krzysztof Halasa List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, Aug 16, 2010 at 12:24 PM, john stultz wrote: > On Mon, Aug 16, 2010 at 4:17 AM, Richard Cochran > A few comments below.... > >> +** PTP user space API >> + >> + =A0 The class driver creates a character device for each registered PT= P >> + =A0 clock. User space programs may control the clock using standardize= d >> + =A0 ioctls. A program may query, enable, configure, and disable the >> + =A0 ancillary clock features. User space can receive time stamped >> + =A0 events via blocking read() and poll(). One shot and periodic >> + =A0 signals may be configured via an ioctl API with semantics similar >> + =A0 to the POSIX timer_settime() system call. > > As I mentioned earlier, I'm not a huge fan of the char device > interface for abstracted PTP clocks. > If it was just the direct hardware access, similar to RTC, which user > apps then use as a timesource, I'd not have much of a problem. But as > I mentioned in an earlier private mail, the abstraction level concerns > me. [snip] > 2) As Arnd already mentioned, the chardev interface seems to duplicate > the clock_gettime/settime() and adjtimex() interfaces. And maybe just to clarify, as I saw your response to Arnd, I'm not suggesting using PTP clocks as clocksources for the internal timekeeping core. Instead I'm trying to understand why PTP clocks need the equivalent of the existing posix clocks/timer interface. Why would only having a read-time interface not suffice? thanks -john