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

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Date:	Tue, 10 May 2016 13:04:37 +0300
From:	Roger Quadros <rogerq@...com>
To:	Felipe Balbi <balbi@...nel.org>
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()

On 10/05/16 12:58, Felipe Balbi wrote:
> 
> Hi,
> 
> Roger Quadros <rogerq@...com> writes:
>> We intend to share this interrupt with the OTG driver an to ensure
>> that irqflags match for the shared interrupt handlers we use
>> request_threaded_irq()
>>
>> If we don't use request_treaded_irq() then forced threaded irq will
>> set IRQF_ONESHOT and this won't match with the OTG IRQ handler's
>> IRQ flags.
>>
>> NOTE: OTG IRQ handler is yet to be added. This is a preparatory step.
>>
>> Signed-off-by: Roger Quadros <rogerq@...com>
>> ---
>>  drivers/usb/dwc3/dwc3-omap.c | 12 +++++++++---
>>  1 file changed, 9 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/usb/dwc3/dwc3-omap.c b/drivers/usb/dwc3/dwc3-omap.c
>> index 59ea35f..6504e94 100644
>> --- a/drivers/usb/dwc3/dwc3-omap.c
>> +++ b/drivers/usb/dwc3/dwc3-omap.c
>> @@ -272,16 +272,22 @@ static irqreturn_t dwc3_omap_interrupt(int irq, void *_omap)
>>  {
>>  	struct dwc3_omap	*omap = _omap;
>>  	u32			reg;
>> +	int			ret = IRQ_NONE;
>>  
>>  	reg = dwc3_omap_read_irqmisc_status(omap);
>>  
>> +	if (reg)
>> +		ret = IRQ_HANDLED;
>> +
>>  	dwc3_omap_write_irqmisc_status(omap, reg);
>>  
>>  	reg = dwc3_omap_read_irq0_status(omap);
>> +	if (reg)
>> +		ret = IRQ_HANDLED;
>>  
>>  	dwc3_omap_write_irq0_status(omap, reg);
>>  
>> -	return IRQ_HANDLED;
>> +	return ret;
>>  }
>>  
>>  static void dwc3_omap_enable_irqs(struct dwc3_omap *omap)
>> @@ -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?

cheers,
-roger