linux-kernel - Re: [PATCH 3/3] clocksource: atmel-pit: Remove irq handler when clock event is unused

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Date:	Sat, 18 Jul 2015 10:20:53 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
cc:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	David Dueck <davidcdueck@...glemail.com>
Subject: Re: [PATCH 3/3] clocksource: atmel-pit: Remove irq handler when
 clock event is unused

On Fri, 17 Jul 2015, Alexandre Belloni wrote:
>  /*
> + * IRQ handler for the timer.
> + */
> +static irqreturn_t at91sam926x_pit_interrupt(int irq, void *dev_id)
> +{
> +	struct pit_data *data = dev_id;
> +
> +	/*
> +	 * irqs should be disabled here, but as the irq is shared they are only
> +	 * guaranteed to be off if the timer irq is registered first.

That's wrong. We run all handlers with interrupts disabled for about 5
years now.

> +	 */
> +	WARN_ON_ONCE(!irqs_disabled());


> +	/* The PIT interrupt may be disabled, and is shared */
> +	if (clockevent_state_periodic(&data->clkevt) &&
> +	    (pit_read(data->base, AT91_PIT_SR) & AT91_PIT_PITS)) {
> +		unsigned nr_ticks;
> +
> +		/* Get number of ticks performed before irq, and ack it */
> +		nr_ticks = PIT_PICNT(pit_read(data->base, AT91_PIT_PIVR));
> +		do {
> +			data->cnt += data->cycle;
> +			data->clkevt.event_handler(&data->clkevt);
> +			nr_ticks--;
> +		} while (nr_ticks);

I don't think you need this loop. You have a proper clocksource
registered so the timekeeping code will handle the lost ticks nicely.


Thanks,

	tglx
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