linux-kernel - Re: [PATCH 03/11] ARM: timer-sp: convert to use CLKSRC

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Message-ID: <514BC265.7080204@gmail.com>
Date:	Thu, 21 Mar 2013 21:31:01 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org, Arnd Bergmann <arnd@...db.de>,
	linus.walleij@...aro.org, haojian.zhuang@...aro.org,
	pawel.moll@....com, john.stultz@...aro.org, tglx@...utronix.de,
	Rob Herring <rob.herring@...xeda.com>
Subject: Re: [PATCH 03/11] ARM: timer-sp: convert to use CLKSRC_OF init

On 03/21/2013 02:35 PM, Russell King - ARM Linux wrote:
> On Wed, Mar 20, 2013 at 05:54:03PM -0500, Rob Herring wrote:
>> +	clk0 = of_clk_get(np, 0);
>> +	if (IS_ERR(clk0))
>> +		clk0 = NULL;
>> +
>> +	/* Get the 2nd clock if the timer has 2 timer clocks */
>> +	if (of_count_phandle_with_args(np, "clocks", "#clock-cells") == 3) {
>> +		clk1 = of_clk_get(np, 1);
>> +		if (IS_ERR(clk1)) {
>> +			pr_err("sp804: %s clock not found: %d\n", np->name,
>> +				(int)PTR_ERR(clk1));
>> +			return;
>> +		}
>> +	} else
>> +		clk1 = clk0;
>> +
>> +	irq = irq_of_parse_and_map(np, 0);
>> +	if (irq <= 0)
>> +		return;
>> +
>> +	of_property_read_u32(np, "arm,sp804-has-irq", &irq_num);
>> +	if (irq_num == 2)
>> +		tmr2_evt = true;
>> +
>> +	__sp804_clockevents_init(base + (tmr2_evt ? TIMER_2_BASE : 0),
>> +				 irq, tmr2_evt ? clk1 : clk0, name);
>> +	__sp804_clocksource_and_sched_clock_init(base + (tmr2_evt ? 0 : TIMER_2_BASE),
>> +						 name, tmr2_evt ? clk0 : clk1, 1);
> 
> This just looks totally screwed to me.
> 
> A SP804 cell has two timers, and has one clock input and two clock
> enable inputs.  The clock input is common to both timers.  The timers
> only count on the rising edge of the clock input when the enable
> input is high.  (the APB PCLK also matters too...)
> 
> Now, the clock enable inputs are controlled by the SP810 system
> controller to achieve different clock rates for each.  So, we *can*
> view an SP804 as having two clock inputs.

Exactly. Effectively, the TIMCLKENx are just dividers of the clock input.

> However, the two clock inputs do not depend on whether one or the
> other has an IRQ or not.  Timer 1 is always clocked by TIMCLK &
> TIMCLKEN1.  Timer 2 is always clocked by TIMCLK & TIMCLKEN2.
> 
> Using the logic above, the clocks depend on how the IRQs are wired
> up... really?  Can you see from my description above why that is
> screwed?  What bearing does the IRQ have on the wiring of the
> clock inputs?

No. I'm simply swapping which timer is used for clksrc vs. clkevt based
on the irq connection DT describes. If only timer 2's irq being hooked
up, then timer 2 is the clkevt. Otherwise I always use timer 1 for the
clkevt because I either have a combined interrupt or timer 1 interrupt
hooked up.

Perhaps re-writing it like this would be more clear:

if (irq_num == 2){
	__sp804_clockevents_init(base + TIMER_2_BASE, irq, clk1, name);
	__sp804_clocksource_and_sched_clock_init(base, name, clk0, 1);
} else {
	__sp804_clockevents_init(base, irq, clk0, name);
	__sp804_clocksource_and_sched_clock_init(base + TIMER_2_BASE,
						name, clk1, 1);
}


Rob
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