Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753498AbaJWSyJ (ORCPT ); Thu, 23 Oct 2014 14:54:09 -0400 Received: from bear.ext.ti.com ([192.94.94.41]:48018 "EHLO bear.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751062AbaJWSyG (ORCPT ); Thu, 23 Oct 2014 14:54:06 -0400 Date: Thu, 23 Oct 2014 13:52:47 -0500 From: Felipe Balbi To: Johan Hovold CC: Felipe Balbi , Alessandro Zummo , Tony Lindgren , =?iso-8859-1?Q?Beno=EEt?= Cousson , Andrew Morton , Lokesh Vutla , Guenter Roeck , , , , , , , , Subject: Re: [PATCH 08/12] rtc: omap: restore irq state after reading TC registers Message-ID: <20141023185247.GB21407@saruman> Reply-To: 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> <20141022105011.GN2113@localhost> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="rJwd6BRFiFCcLxzm" Content-Disposition: inline In-Reply-To: <20141022105011.GN2113@localhost> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --rJwd6BRFiFCcLxzm Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Oct 22, 2014 at 12:50:11PM +0200, Johan Hovold wrote: > 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, > > > >=20 > > > > On Thu, Oct 09, 2014 at 09:06:30PM +0200, Johan Hovold wrote: > > > > > Make sure to restore local irq state when reading the timer/calen= dar > > > > > (TC) registers, so that omap_rtc_read_time() can be called with > > > > > interrupts disabled. > > > > >=20 > > > > > Signed-off-by: Johan Hovold > > > > > --- > > > > > drivers/rtc/rtc-omap.c | 6 ++++-- > > > > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > >=20 > > > > > 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) > > > > > =20 > > > > > static int omap_rtc_read_time(struct device *dev, struct rtc_tim= e *tm) > > > > > { > > > > > + unsigned long flags; > > > > > + > > > > > /* we don't report wday/yday/isdst ... */ > > > > > - local_irq_disable(); > > > > > + local_irq_save(flags); > > > >=20 > > > > 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. > > >=20 > > > The driver uses local_irq* throughout to guarantee registers are not > > > read or written during an update event. > > >=20 > > > 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. > > >=20 > > > Do you suggest doing this conversion as part of, or on top of, this > > > series? > >=20 > > probably on top of is. Safer that way. >=20 > I didn't include this conversion in v2 as you may have noticed. In fact, > I'm not even sure it should be done. >=20 > 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: >=20 > "If the ARM accesses the TC registers outside of the access > period, then the access is not guaranteed." >=20 > 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). that's alright, better not to change the behavior in this case. But as a future patch, you might want to convert this to a raw_spinlock. That won't get preempted. --=20 balbi --rJwd6BRFiFCcLxzm Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJUSU5/AAoJEIaOsuA1yqRE6f8QAKZrfi0zty3h+uHjFdm3aHFA 6qh7bjLtJkLFxcCiMG1ZchkyQSbeYY/3hEmv8YjrsFKj+WHohw5yNP6ZDbmCftyt eflAhFgjnjm+8XtO763PX10O7OFUJWu4sibsj81KbBV4i/bL5NcbI4NKJOmUYBoD IUXO3bbqIXbeCmcMFkghGf8QMHrmDcAKQMtfdwAe53KtlY3bTPoSPk5uUsS+EwMY ULlo4d/TKb5ol0jPnDlBw/fQ8rCcSJYdKdzQKnH5TQ+qLbA+9JLdHQLcBnirr9yC pkDbnA3BOWHfvnrMmsAzpFtP479XPXhlv8anYjgT8qcw7gJv0La1zBXDBR4zwiiJ 3olgs7/yV83T8Y4tQyuY5sPQbpwqsh/dJo1Hel4Ljq6m+MuBexSo/1g1IBWEE9Qv 5G1NgKklvev6Q2uhio3Ly2u4bWPmQBwQy45OzGzSFrc5nHG9UxJJz0yaQspLabW/ NpRzv7GE2Vs30Tx0hrcxP96HhMKy8Sn6tSEWrdMzzVOHbzKg6LJmT4LqIZP4A1fN k2YAbiGByZztbMvpfSOCrw3TNcayjy2Pw3NL2iCdnVp00UJSpundZBqF3nIo+yIc B6GEmZP1z1EALh12odtFC0Z0C91X/tzvguRK+Yp+m7XHobpwNg/sykwLUdu7iku7 E9hynAD3kQcuwvbVKqY2 =6iin -----END PGP SIGNATURE----- --rJwd6BRFiFCcLxzm-- -- 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/