linux-kernel - Re: [RFC PATCH 02/10] clockevents/drivers: add MPS2 Timer driver

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Message-ID: <5655D1F7.2030202@arm.com>
Date:	Wed, 25 Nov 2015 15:21:27 +0000
From:	Vladimir Murzin <vladimir.murzin@....com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>, arnd@...db.de,
	linux@....linux.org.uk, gregkh@...uxfoundation.org,
	tglx@...utronix.de, u.kleine-koenig@...gutronix.de,
	afaerber@...e.de, mcoquelin.stm32@...il.com
CC:	Mark.Rutland@....com, Pawel.Moll@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	jslaby@...e.cz, robh+dt@...nel.org, devicetree@...r.kernel.org,
	linux-serial@...r.kernel.org, linux-api@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 02/10] clockevents/drivers: add MPS2 Timer driver

On 25/11/15 15:10, Daniel Lezcano wrote:
> On 11/25/2015 03:51 PM, Vladimir Murzin wrote:
>> Hi Daniel,
>>
>> Thanks for you review, I agree on all concerns raised and address them
>> in the next version. Just some points to confirm below (I left only
>> relevant parts).
>>
>>>> +static irqreturn_t mps2_timer_interrupt(int irq, void *dev_id)
>>>> +{
>>>> +    struct clockevent_mps2 *ce = dev_id;
>>>> +    u32 status = readl(ce->reg + TIMER_INT);
>>>> +
>>>> +    if (!status)
>>>> +        return IRQ_NONE;
>>>
>>> Why that could happen ? Add a comment.
>>>
>>
>> Sort of defensive programming, I never seen it happens, but just in case
>> of spurious interrupts... Do you prefer to get rid of this check or
>>
>>      /* spurious interrupt? */
>>      if (!status)
>>          return IRQ_NONE;
>>
>> would be fine to you?
> 
> Yes, that would be fine, but if it does never happen, we don't really
> need this check. If you prefer to make sure there isn't a spurious
> interrupt and considering it shouldn't happen, a pr_info trace may help
> to spot this misbehavior.
> 

Good, I'll put pr_warn("spurious interrupt\n") then.

>>>> +}
>>>> +
>>>> +static void __init mps2_timer_init(struct device_node *np)
>>>> +{
>>>> +    static int clksrc;
>>>> +
>>>> +    if (!clksrc && !mps2_clocksource_init(np))
>>>> +        clksrc = 1;
>>>> +    else
>>>> +        mps2_clockevents_init(np);
>>>
>>> That assumes the clocksource is defined before the clockevents in the
>>> DT. If it is not the case, the mps2_clocksource_init will fail (and spit
>>> errors) and mps2_clockevents_init() won't be called.
>>>
>>
>> Does following (stolen from efm32) look better to you?
>>
>> static void __init mps2_timer_init(struct device_node *np)
>> {
>>     static int has_clocksource, has_clockevent;
>>     int ret;
>>
>>     if (!has_clocksource) {
>>         ret = mps2_clocksource_init(np);
>>         if (!ret) {
>>             has_clocksource = 1;
>>             return;
>>         }
>>     }
>>
>>     if (!has_clockevent) {
>>         ret = mps2_clockevent_init(np);
>>         if (!ret) {
>>             has_clockevent = 1;
>>             return;
>>         }
>>     }
>> }
> 
> Yes.
> 
> I don't like to have a "CLOCKSOURCE_OF_DECLARE" to initialize a
> clockevent but I can't blame you, this is what is done in the other
> drivers.

Thanks for your time!

Vladimir

> 
>>>> +}
>>>> +
>>>> +CLOCKSOURCE_OF_DECLARE(mps2_timer, "arm,mps2-timer", mps2_timer_init);
>>>>
>>>
>>>
>>
> 
> 

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