From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 347A0C3F2CD for ; Tue, 3 Mar 2020 02:02:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 138B324677 for ; Tue, 3 Mar 2020 02:02:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727018AbgCCCCE (ORCPT ); Mon, 2 Mar 2020 21:02:04 -0500 Received: from mga04.intel.com ([192.55.52.120]:22013 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726773AbgCCCCD (ORCPT ); Mon, 2 Mar 2020 21:02:03 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 02 Mar 2020 18:02:03 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,509,1574150400"; d="scan'208";a="274004683" Received: from wtczc53028gn.jf.intel.com (HELO skl-build) ([10.54.87.17]) by fmsmga002.fm.intel.com with ESMTP; 02 Mar 2020 18:02:02 -0800 Date: Mon, 2 Mar 2020 18:01:48 -0800 From: "Christopher S. Hall" To: Richard Cochran Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, hpa@zytor.com, mingo@redhat.com, x86@kernel.org, jacob.e.keller@intel.com, davem@davemloft.net, sean.v.kelley@intel.com Subject: Re: [Intel PMC TGPIO Driver 0/5] Add support for Intel PMC Time GPIO Driver with PHC interface changes to support additional H/W Features Message-ID: <20200303020148.GB15531@skl-build> References: <20191211214852.26317-1-christopher.s.hall@intel.com> <20200203040838.GA5851@localhost> <20200225233707.GA32079@skl-build> <20200226024707.GA10271@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200226024707.GA10271@localhost> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Richard, On Tue, Feb 25, 2020 at 06:47:07PM -0800, Richard Cochran wrote: > On Tue, Feb 25, 2020 at 03:37:07PM -0800, Christopher S. Hall wrote: > > On Sun, Feb 02, 2020 at 08:08:38PM -0800, Richard Cochran wrote: > > > The TGPIO input clock, the ART, is a free running counter, but you > > > want to support frequency adjustments. Use a timecounter cyclecounter > > > pair. > > > > I'm concerned about the complexity that the timecounter adds to > > the driver. Specifically, the complexity of dealing with any rate mismatches > > between the timecounter and the periodic output signal. The phase > > error between the output and timecounter needs to be zero. > > If I understood correctly, the device's outputs are generated from a > non-adjustable counter. So, no matter what, you will have the problem > of changing the pulse period in concert with the user changing the > desired frequency. > > > This leaves the PHC API behavior as it is currently and uses the frequency > > adjust API to adjust the output rate. > > > > > Let the user dial a periodic output signal in the normal way. > > > > > > Let the user change the frequency in the normal way, and during this > > > call, adjust the counter values accordingly. > > > > Yes to both of the above. > > So, why then do you need this? > > +#define PTP_EVENT_COUNT_TSTAMP2 \ > + _IOWR(PTP_CLK_MAGIC, 19, struct ptp_event_count_tstamp) > > If you can make the device work with the existing user space API, > > ioctl(fd, PTP_PEROUT_REQUEST2, ...); > while (1) { > clock_adjtimex(FD_TO_CLOCKID(fd), ...); > } > > that would be ideal. But I will push back on anything like the > following. > > ioctl(fd, PTP_PEROUT_REQUEST2, ...); > while (1) { > clock_adjtimex(FD_TO_CLOCKID(fd), ...); > ioctl(fd, PTP_EVENT_COUNT_TSTAMP, ...); > } > > But maybe I misunderstood? Thank you for the feedback, but Thomas wants to see this as an extension of GPIO. I'll work on an RFC patch for that instead. > Thanks, > Richard Thanks, Christopher