linux-kernel - Re: [PATCH v7 1/5] usb: dwc3: omap: use request_threaded

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Message-ID: <87y47hexja.fsf@linux.intel.com>
Date:	Wed, 11 May 2016 12:47:37 +0300
From:	Felipe Balbi <balbi@...nel.org>
To:	Roger Quadros <rogerq@...com>
Cc:	tony@...mide.com, Joao.Pinto@...opsys.com,
	sergei.shtylyov@...entembedded.com, peter.chen@...escale.com,
	jun.li@...escale.com, grygorii.strashko@...com,
	yoshihiro.shimoda.uh@...esas.com, nsekhar@...com, b-liu@...com,
	linux-usb@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 1/5] usb: dwc3: omap: use request_threaded_irq()


Hi,

Roger Quadros <rogerq@...com> writes:
>> Roger Quadros <rogerq@...com> writes:
>>>>> @@ -497,8 +503,8 @@ static int dwc3_omap_probe(struct platform_device *pdev)
>>>>>  	/* check the DMA Status */
>>>>>  	reg = dwc3_omap_readl(omap->base, USBOTGSS_SYSCONFIG);
>>>>>  
>>>>> -	ret = devm_request_irq(dev, omap->irq, dwc3_omap_interrupt, 0,
>>>>> -			"dwc3-omap", omap);
>>>>> +	ret = devm_request_threaded_irq(dev, omap->irq, dwc3_omap_interrupt,
>>>>> +					NULL, 0, "dwc3-omap", omap);
>>>>
>>>> if you're using threaded_irq, it's better to have a NULL top half and
>>>> valid bottom half.
>>>
>>> But in this case we don't need a bottom half as there is nothing to do :).
>>>
>>>>
>>>> In fact, since this will be shared, you could do a proper preparation
>>>> and on top half check if $this device generated the IRQ and
>>>> conditionally schedule the bottom half. Don't forget to mask device's
>>>> interrupts from top half so you can run without IRQF_ONESHOT.
>>>>
>>>
>>> Why do this at all if there is nothing to do in the bottom half?
>> 
>> oh, but there is :-)
>> 
>> The whole idea of threaded IRQs is that you spend as little time as
>> possible on top half and the (strong) recommendation is that you *only*
>> check if $this device generated the interrupt. Note that "checking if
>> $this device generated the interrupt" will be mandatory as soon as you
>> mark the IRQ line as shared ;-)
>> 
>> So here's how this should look like:
>> 
>> static irqreturn_t dwc3_omap_interrupt(int irq, void *_omap)
>> {
>>         struct dwc3_omap *omap = _omap;
>>         u32 reg;
>> 
>>         reg = readl(IRQSTATUS)
>>         if (reg) {
>>                 mask_interrupts(omap);
>>         	return IRQ_WAKE_THREAD;
>>         }
>> 
>> 	return IRQ_HANDLED;
>
> This should be IRQ_NONE right?

possibly, testing will say ;-)

>> static irqreturn_t dwc3_omap_threaded_interrupt(int irq, void *_omap)
>> {
>>         struct dwc3_omap *omap = _omap;
>>         u32 reg;
>> 
>>         spin_lock(&omap->lock);
>
> Do we really need a spin_lock for the dwc3-omap driver?
> Currently we won't be doing anything other than just
> clearing the irqstatus and re-enabling the interrupts.

well, if there's no possibility of races, then no. But only testing will
say for sure, I guess. I didn't really go through the entire thing just
to a write a quick little template :-p

-- 
balbi

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