linux-kernel - RE: [PATCH 3/3] RTC: Update seconds time programming logic

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Date:	Wed, 20 Apr 2016 13:37:30 +0000
From:	Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
CC:	Alessandro Zummo <a.zummo@...ertech.it>,
	Soren Brinkmann <sorenb@...inx.com>,
	Michal Simek <michals@...inx.com>,
	"rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Punnaiah Choudary Kalluri <punnaia@...inx.com>,
	Anirudha Sarangi <anirudh@...inx.com>,
	Srikanth Vemula <svemula@...inx.com>,
	Srinivas Goud <sgoud@...inx.com>
Subject: RE: [PATCH 3/3] RTC: Update seconds time programming logic

Hi Alexandre,

Thanks for reviewing the patch, I will sent v2 with the changes updated.

Thanks,
Anurag Kumar V

> -----Original Message-----
> From: Alexandre Belloni [mailto:alexandre.belloni@...e-electrons.com]
> Sent: Wednesday, April 20, 2016 5:32 PM
> To: Anurag Kumar Vulisha <anuragku@...inx.com>
> Cc: Alessandro Zummo <a.zummo@...ertech.it>; Soren Brinkmann
> <sorenb@...inx.com>; Michal Simek <michals@...inx.com>; rtc-
> linux@...glegroups.com; linux-arm-kernel@...ts.infradead.org; linux-
> kernel@...r.kernel.org; Punnaiah Choudary Kalluri <punnaia@...inx.com>;
> Anirudha Sarangi <anirudh@...inx.com>; Srikanth Vemula
> <svemula@...inx.com>; Srinivas Goud <sgoud@...inx.com>
> Subject: Re: [PATCH 3/3] RTC: Update seconds time programming logic
> 
> On 20/04/2016 at 10:31:06 +0000, Anurag Kumar Vulisha wrote :
> > > Yeas, I understood that. But my question was whether the interrupt
> > > handling was necessary at all.
> > > Instead of waiting for an interrupt to set time_updated, can't you
> > > simply read RTC_INT_STS and check for the RTC_INT_SEC bit in
> > > xlnx_rtc_read_time() ?
> > >
> > > Something like:
> > >
> > > status = readl(xrtcdev->reg_base + RTC_INT_STS) if (status &
> RTC_INT_SEC)
> > >       rtc_time64_to_tm(readl(xrtcdev->reg_base + RTC_CUR_TM), tm);
> > > else
> > >       rtc_time64_to_tm(readl(xrtcdev->reg_base + RTC_SET_TM_RD) - 1,
> > > tm);
> > >
> > > It all depends on whether the RTC_INT_SEC bit in RTC_INT_STS is
> > > being updated even when it is not enabled as an interrupt.
> > >
> >
> > The above said logic will work if we doesn't clear the RTC_INT_STS
> > register after the RTC_INT_SEC bit is set, this happens only if
> > interrupts are not enabled. If interrupts are enabled we will be clearing the
> RTC_INT_STS every time in the interrupt handler.
> > And moreover we need to return time from RTC_SET_TM_RD only if time is
> > requested within 1 sec span after programming the time only , so this is
> required only for one time.
> > Since we are clearing the RTC_INT_STS in our interrupt handler, we
> > might end up in giving the wrong time to the user when requested.So I
> think this logic might not work.
> > Please correct me if am wrong.
> >
> 
> Simply stop clearing RTC_INT_SEC from RTC_INT_STS in the interrupt
> handler.
> 
> You can also remove
> 	if (status & RTC_INT_SEC)
> 		rtc_update_irq(xrtcdev->rtc, 1, RTC_IRQF | RTC_UF);
> 
> as it will not be used. Update interrupts are handled by the core using timers
> anyway. And as you can see, there was no code enabling RTC_INT_SEC in
> RTC_INT_EN before your patch.
> 
> --
> Alexandre Belloni, Free Electrons
> Embedded Linux, Kernel and Android engineering http://free-electrons.com