linux-kernel - Re: [PATCH 1/2] clocksource/drivers/timer-ti-dm: Prepare to handle dra7 timer wrap issue

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Date:   Mon, 22 Mar 2021 19:23:36 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>, Keerthy <j-keerthy@...com>,
        linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Tero Kristo <kristo@...nel.org>
Subject: Re: [PATCH 1/2] clocksource/drivers/timer-ti-dm: Prepare to handle
 dra7 timer wrap issue

On 22/03/2021 17:33, Tony Lindgren wrote:
> Hi,
> 
> * Daniel Lezcano <daniel.lezcano@...aro.org> [210322 15:56]:
>> On 04/03/2021 08:37, Tony Lindgren wrote:
>>> There is a timer wrap issue on dra7 for the ARM architected timer.
>>> In a typical clock configuration the timer fails to wrap after 388 days.
>>>
>>> To work around the issue, we need to use timer-ti-dm timers instead.
>>>
>>> Let's prepare for adding support for percpu timers by adding a common
>>> dmtimer_clkevt_init_common() and call it from dmtimer_clockevent_init().
>>> This patch makes no intentional functional changes.
>>>
>>> Signed-off-by: Tony Lindgren <tony@...mide.com>
>>> ---
>>
>> [ ... ]
>>
>>> @@ -575,33 +574,60 @@ static int __init dmtimer_clockevent_init(struct device_node *np)
>>>  	 */
>>>  	writel_relaxed(OMAP_TIMER_CTRL_POSTED, t->base + t->ifctrl);
>>>  
>>> +	if (dev->cpumask == cpu_possible_mask)
>>> +		irqflags = IRQF_TIMER;
>>> +	else
>>> +		irqflags = IRQF_TIMER | IRQF_NOBALANCING;
>>
>> Can you explain the reasoning behind the test above ?
> 
> In the per cpu case we assign one dmtimer per cpu, and we want the
> interrupt handling on the assigned CPU. In the per cpu case we have
> the cpu specified with dev->cpumask unlike for the normal clockevent
> case.
> 
> In the per cpu dmtimer case the interrupt line is not wired per cpu
> though, so I don't think we want to add IRQF_PERCPU here.

If it is per cpu, then the parameter will be cpumask_of(cpu). If there
is one cpu, no balancing can happen and then the IRQF_NOBALANCING is not
needed, neither this test and the irqflags, right?



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