linux-kernel - RE: [PATCH 3/4] ARM: Xilinx: Adding timer support to the platform

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Date:	Mon, 7 Feb 2011 08:01:37 -0700
From:	John Linn <John.Linn@...inx.com>
To:	Jamie Iles <jamie@...ieiles.com>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <linux@....linux.org.uk>,
	<catalin.marinas@....com>, <glikely@...retlab.ca>,
	Kiran Sutariya <kiran.sutariya@...fochips.com>
Subject: RE: [PATCH 3/4] ARM: Xilinx: Adding timer support to the platform

> -----Original Message-----
> From: Jamie Iles [mailto:jamie@...ieiles.com]
> Sent: Monday, February 07, 2011 7:59 AM
> To: John Linn
> Cc: Jamie Iles; linux-arm-kernel@...ts.infradead.org;
linux-kernel@...r.kernel.org;
> linux@....linux.org.uk; catalin.marinas@....com; glikely@...retlab.ca;
Kiran Sutariya
> Subject: Re: [PATCH 3/4] ARM: Xilinx: Adding timer support to the
platform
> 
> On Mon, Feb 07, 2011 at 07:16:01AM -0700, John Linn wrote:
> > > -----Original Message-----
> > > From: Jamie Iles [mailto:jamie@...ieiles.com]
> > > Sent: Saturday, February 05, 2011 6:04 PM
> > > To: John Linn
> > > Cc: linux-arm-kernel@...ts.infradead.org;
> > linux-kernel@...r.kernel.org; linux@....linux.org.uk;
> > > catalin.marinas@....com; glikely@...retlab.ca; Kiran Sutariya
> > > Subject: Re: [PATCH 3/4] ARM: Xilinx: Adding timer support to the
> > platform
> > >
> > > Hi John,
> > >
> > > A couple more nitpicks.
> > >
> > > Jamie
> > >
> > > On Sat, Feb 05, 2011 at 09:17:16AM -0700, John Linn wrote:
> > > > +static irqreturn_t xttcpss_clock_event_interrupt(int irq, void
> > *dev_id)
> > > > +{
> > > > +	struct clock_event_device *evt = &xttcpss_clockevent;
> > > > +	struct xttcpss_timer *timer = dev_id;
> > > > +	u32 ctrl_reg;
> > > > +
> > > > +	/* Acknowledge the interrupt and call event handler */
> > > > +	xttcpss_write(timer->base_addr + XTTCPSS_ISR_OFFSET,
> > > > +		xttcpss_read(timer->base_addr +
XTTCPSS_ISR_OFFSET));
> > > > +
> > > > +	if (timer->mode == CLOCK_EVT_MODE_ONESHOT) {
> > > > +
> > > > +		/* Disable the counter as it would keep running.
*/
> > > > +		ctrl_reg = xttcpss_read(timer->base_addr +
> > > > +
XTTCPSS_CNT_CNTRL_OFFSET);
> > > > +		ctrl_reg |= ~(XTTCPSS_CNT_CNTRL_ENABLE_MASK);
> > >
> > > The clock events framework should reprogram the next event so you
> > don't
> > > actually need to disable the timer here.  Once the event handler
has
> > > been called the timer will be reenabled with a new period, and as
> > we're
> > > running with interrupts disabled here we don't need to stop the
timer.
> > >
> >
> > What about if there's not another event to be started?
> 
> Then the clockevents code can set the mode to CLOCK_EVT_MODE_SHUTDOWN
> and this should disable the timer.  For NOHZ, AFAICT the
> clockevents/tick code will make sure that the next tick always falls
> within your max_delta_ns.
> 
> Jamie

Thanks, appreciate that help as I'm still learning more on the clock
mgmt.

Sounds good, I can stop it and test that.

-- John

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