linux-kernel - Re: [PATCH 08/12] rtc: omap: restore irq state after reading TC registers

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Date:	Sat, 11 Oct 2014 19:47:58 -0500
From:	Felipe Balbi <balbi@...com>
To:	Johan Hovold <johan@...nel.org>
CC:	Felipe Balbi <balbi@...com>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Tony Lindgren <tony@...mide.com>,
	Benoît Cousson <bcousson@...libre.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Lokesh Vutla <lokeshvutla@...com>,
	Guenter Roeck <linux@...ck-us.net>,
	Colin Foe-Parker <colin.foeparker@...icpd.com>,
	<nsekhar@...com>, <t-kristo@...com>, <j-keerthy@...com>,
	<linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<devicetree@...r.kernel.org>, <rtc-linux@...glegroups.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/12] rtc: omap: restore irq state after reading TC
 registers

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 <johan@...nel.org>
> > > ---
> > >  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.

-- 
balbi

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