Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932962AbaJVKxR (ORCPT ); Wed, 22 Oct 2014 06:53:17 -0400 Received: from mail-la0-f47.google.com ([209.85.215.47]:54959 "EHLO mail-la0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932458AbaJVKxO (ORCPT ); Wed, 22 Oct 2014 06:53:14 -0400 X-Google-Original-Sender: Date: Wed, 22 Oct 2014 12:50:11 +0200 From: Johan Hovold To: Felipe Balbi Cc: Johan Hovold , Alessandro Zummo , Tony Lindgren , =?iso-8859-1?Q?Beno=EEt?= Cousson , Andrew Morton , Lokesh Vutla , Guenter Roeck , nsekhar@ti.com, t-kristo@ti.com, j-keerthy@ti.com, linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org, rtc-linux@googlegroups.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 08/12] rtc: omap: restore irq state after reading TC registers Message-ID: <20141022105011.GN2113@localhost> References: <1412881594-25678-1-git-send-email-johan@kernel.org> <1412881594-25678-9-git-send-email-johan@kernel.org> <20141010180225.GT31348@saruman> <20141011101201.GC18988@localhost> <20141012004758.GB21128@saruman> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141012004758.GB21128@saruman> User-Agent: Mutt/1.5.22 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Oct 11, 2014 at 07:47:58PM -0500, Felipe Balbi wrote: > On Sat, Oct 11, 2014 at 12:12:01PM +0200, Johan Hovold wrote: > > On Fri, Oct 10, 2014 at 01:02:31PM -0500, Felipe Balbi wrote: > > > Hi, > > > > > > On Thu, Oct 09, 2014 at 09:06:30PM +0200, Johan Hovold wrote: > > > > Make sure to restore local irq state when reading the timer/calendar > > > > (TC) registers, so that omap_rtc_read_time() can be called with > > > > interrupts disabled. > > > > > > > > Signed-off-by: Johan Hovold > > > > --- > > > > drivers/rtc/rtc-omap.c | 6 ++++-- > > > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/drivers/rtc/rtc-omap.c b/drivers/rtc/rtc-omap.c > > > > index 0ef016553a97..62e2e9a9887a 100644 > > > > --- a/drivers/rtc/rtc-omap.c > > > > +++ b/drivers/rtc/rtc-omap.c > > > > @@ -239,8 +239,10 @@ static void bcd2tm(struct rtc_time *tm) > > > > > > > > static int omap_rtc_read_time(struct device *dev, struct rtc_time *tm) > > > > { > > > > + unsigned long flags; > > > > + > > > > /* we don't report wday/yday/isdst ... */ > > > > - local_irq_disable(); > > > > + local_irq_save(flags); > > > > > > you should really convert these to a real spin_lock_irq*(), that's > > > because local_irq* do not get re-written with RT patchset, so this > > > pretty much "breaks" RT. > > > > The driver uses local_irq* throughout to guarantee registers are not > > read or written during an update event. > > > > In fact, at least on AM33xx, this is not even necessary when reading (as > > opposed to writing) the TC registers, but I did not dare change that > > without knowing how the legacy platforms work in this respect. > > > > Do you suggest doing this conversion as part of, or on top of, this > > series? > > probably on top of is. Safer that way. I didn't include this conversion in v2 as you may have noticed. In fact, I'm not even sure it should be done. Using local_irq* "breaks" RT, but if we change it to spin_lock_irq* and RT preempts us, we may miss the 15us access window which would break the driver: "If the ARM accesses the TC registers outside of the access period, then the access is not guaranteed." On am33xx this only affects updating the TC (timer/calendar) or alarm registers, but the driver currently disables interrupts also on reading the time (possibly because the early IP revisions did not have the shadow read registers). Johan -- 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/