From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1751125AbbJELNs (ORCPT <rfc822;w@1wt.eu>);
	Mon, 5 Oct 2015 07:13:48 -0400
Received: from muru.com ([72.249.23.125]:55940 "EHLO muru.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1750768AbbJELNq (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 5 Oct 2015 07:13:46 -0400
Date: Mon, 5 Oct 2015 04:13:41 -0700
From: Tony Lindgren <tony@atomide.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>,
        linux-arm-kernel@lists.infradead.org, balbi@ti.com,
        Alexandre Courbot <gnurou@gmail.com>,
        Stephen Warren <swarren@wwwdotorg.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thierry Reding <thierry.reding@gmail.com>, linux-tegra@vger.kernel.org,
        tglx@linutronix.de,
        Linux OMAP Mailing List <linux-omap@vger.kernel.org>
Subject: Re: [RFC/PATCH 00/11] arm: omap: counter32k rework
Message-ID: <20151005111341.GY23801@atomide.com>
References: <1443559446-26969-1-git-send-email-balbi@ti.com>
 <560DAFC5.50003@linaro.org>
 <20151005105554.GV23801@atomide.com>
 <9068678.D8T0aRhgnK@wuerfel>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <9068678.D8T0aRhgnK@wuerfel>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

* Arnd Bergmann <arnd@arndb.de> [151005 04:08]:
> On Monday 05 October 2015 03:55:55 Tony Lindgren wrote:
> > * Daniel Lezcano <daniel.lezcano@linaro.org> [151001 15:16]:
> > > On 09/30/2015 04:49 PM, Arnd Bergmann wrote:
> > > >On Wednesday 30 September 2015 16:42:21 Arnd Bergmann wrote:
> > > >>
> > > >>TEGRA folks: the tegra_read_persistent_clock() implementation apparently
> > > >>predates the Tegra RTC driver and I wonder if they actually do the
> > > >>right thing in combination. Could it be that the wall time forwards
> > > >>twice as fast as it should during resume when the RTC driver is loaded?
> > > >>Could it be that we can simply remove  tegra_read_persistent_clock()
> > > >>and the register_persistent_clock() infrastructure?
> > > >>
> > > >
> > > >I found the 'sleeptime_injected' variable now, which takes care of
> > > >forwarding the clock by the correct amount.
> > > >
> > > >I also found the CLOCK_SOURCE_SUSPEND_NONSTOP flag next to it, which
> > > >should let us use the counter32k driver to provide the correct
> > > >time during suspend without the omap_read_persistent_clock() function.
> > > >We should be able to just delete that code.
> > > >
> > > >If we decide to also delete the tegra_read_persistent_clock()
> > > >function, we can remove the registration too.
> > > 
> > > 
> > > +1
> > 
> > We could maybe have read_persistent_clock() just check for the
> > CLOCK_SOURCE_SUSPEND_NONSTOP flag?
> 
> timekeeping_resume() already ignores the persistent clock values if
> the clocksource has this set. Do you mean we should additionally
> not call the read_persistent_clock() function at all to safe a
> few cycles reading that value?

Hmm no I mean if we have CLOCK_SOURCE_SUSPEND_NONSTOP we can
automatically make read_persistent_clock() use that if nothing
else got registered.

> How expensive is the function?

Usually the persistent clock is on some interconnect, so it is
way slower compared to a local timer. It doubt it makes a
difference in timekeeping_resume() though :)

Regards,

Tony