linux-kernel - Re: [PATCH v2 5/6] irqchip: gicv3-its: add support for power down

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Date:	Tue, 17 Feb 2015 20:27:58 +0800
From:	"Yun Wu (Abel)" <wuyun.wu@...wei.com>
To:	Marc Zyngier <marc.zyngier@....com>
CC:	"tglx@...utronix.de" <tglx@...utronix.de>,
	"jason@...edaemon.net" <jason@...edaemon.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/6] irqchip: gicv3-its: add support for power down

On 2015/2/17 19:11, Marc Zyngier wrote:

> On Tue, 17 Feb 2015 10:15:15 +0000
> "Yun Wu (Abel)" <wuyun.wu@...wei.com> wrote:
> 
>> On 2015/2/17 17:29, Marc Zyngier wrote:
>>
>>> On Sun, 15 Feb 2015 09:32:02 +0000
>>> Yun Wu <wuyun.wu@...wei.com> wrote:
>>>
>>>> It's unsafe to change the configurations of an activated ITS
>>>> directly since this will lead to unpredictable results. This patch
>>>> guarantees a safe quiescent status before initializing an ITS.
>>>
>>> Please change the title of this patch to reflect what it actually
>>> does. Nothing here is about powering down anything.
>>
>> My miss, I will fix this in next version.
>>
>>>
>>>> Signed-off-by: Yun Wu <wuyun.wu@...wei.com>
>>>> ---
>>>>  drivers/irqchip/irq-gic-v3-its.c | 32
>>>> ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+)
>>>>
>>>> diff --git a/drivers/irqchip/irq-gic-v3-its.c
>>>> b/drivers/irqchip/irq-gic-v3-its.c index 42c03b2..29eb665 100644
>>>> --- a/drivers/irqchip/irq-gic-v3-its.c
>>>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>>>> @@ -1321,6 +1321,31 @@ static const struct irq_domain_ops
>>>> its_domain_ops = { .deactivate		=
>>>> its_irq_domain_deactivate, };
>>>>
>>>> +static int its_check_quiesced(void __iomem *base)
>>>> +{
>>>> +	u32 count = 1000000;	/* 1s */
>>>> +	u32 val;
>>>> +
>>>> +	val = readl_relaxed(base + GITS_CTLR);
>>>> +	if (val & GITS_CTLR_QUIESCENT)
>>>> +		return 0;
>>>> +
>>>> +	/* Disable the generation of all interrupts to this ITS */
>>>> +	val &= ~GITS_CTLR_ENABLE;
>>>> +	writel_relaxed(val, base + GITS_CTLR);
>>>> +
>>>> +	/* Poll GITS_CTLR and wait until ITS becomes quiescent */
>>>> +	while (count--) {
>>>> +		val = readl_relaxed(base + GITS_CTLR);
>>>> +		if (val & GITS_CTLR_QUIESCENT)
>>>> +			return 0;
>>>> +		cpu_relax();
>>>> +		udelay(1);
>>>> +	}
>>>
>>> You're now introducing a third variant of a 1s timeout loop. Notice
>>> a pattern?
>>>
>>
>> I am not sure I know exactly what you suggest. Do you mean I should
>> code like below to keep the coding style same as the other 2 loops?
>>
>> 	while (1) {
>> 		val = readl_relaxed(base + GITS_CTLR);
>> 		if (val & GITS_CTLR_QUIESCENT)
>> 			return 0;
>>
>> 		count--;
>> 		if (!count)
>> 			return -EBUSY;
>>
>> 		cpu_relax();
>> 		udelay(1);
>> 	}
> 
> That'd be a good start. But given that this is starting to be a common
> construct, it could probably be rewritten as:
> 
> static int its_poll_timeout(struct its_node *its, void *data,
>                             int (*fn)(struct its_node *its,
>                                       void *data))
> {
> 	while (1) {
> 		if (!fn(its, data))
> 			return 0;
> 
> 		...
> 	}
> }
> 
> and have the call sites to provide the right utility function. We also
> have two similar timeout loops in the main GICv3 driver, so there
> should be room for improvement.
> 
> Thoughts?
> 

It looks fine to me. I will make some improvement in the next version after
Chinese Spring Festival. :)

Thanks,
	Abel

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