linux-kernel - Re: [PATCH 1/2] input: ti_tsc: Enable shared IRQ for TSC

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Date:	Mon, 5 Aug 2013 15:42:54 -0700
From:	Russ Dill <Russ.Dill@...com>
To:	Zubair Lutfullah: <zubair.lutfullah@...il.com>, ;
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jonathan Cameron <jic23@...nel.org>, <jic23@....ac.uk>,
	<linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-input@...r.kernel.org>, <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 1/2] input: ti_tsc: Enable shared IRQ for TSC

On 08/05/2013 10:02 AM, Zubair Lutfullah : wrote:
> On Mon, Aug 05, 2013 at 09:12:56AM -0700, Dmitry Torokhov wrote:
>>>> Touchscreen and ADC share the same IRQ line from parent MFD core.
>>>> Previously only Touchscreen was interrupt based.
>>>> With continuous mode support added in ADC driver, driver requires
>>>> interrupt to process the ADC samples, so enable shared IRQ flag bit for
>>>> touchscreen.
>>>>
>>>> @@ -260,8 +260,18 @@ static irqreturn_t titsc_irq(int irq, void *dev)
>>>>  	unsigned int fsm;
>>>>  
>>>> +	/*
>>>> +	 * ADC and touchscreen share the IRQ line.
>>>> +	 * FIFO1 threshold, FIFO1 Overrun and FIFO1 underflow
>>>> +	 * interrupts are used by ADC,
>>>> +	 * hence return from touchscreen IRQ handler if FIFO1
>>>> +	 * related interrupts occurred.
>>>> +	 */
>>>> +	if ((status & IRQENB_FIFO1THRES) ||
>>>> +			(status & IRQENB_FIFO1OVRRUN) ||
>>>> +			(status & IRQENB_FIFO1UNDRFLW))
>>>> +		return IRQ_NONE;
>>>> +	else if (status & IRQENB_FIFO0THRES) {
>>
>> What happens if both parts have data at the same time? Can both
>> IRQENB_FIFO1THRES and IRQENB_FIFO0THRES be signalled? What will happen
>> in this case?
> 
> If ADC is sampling and someone is touching the TSC, both interrupts
> can signal so closely that for the purpose of the kernel,
> they can be seen as signaled together.
> 
> FIFO 1 used only by ADC and FIFO1THRES handler is inside the iio/adc driver
> FIFO 0 used only by TSC and FIFO0THRES handler is inside the input/touchscreen
> 
> Note: These are level interrupts.
> 
> I would like some input on how to handle such a situation. 
> 
> Thanks
> Zubair Lutfullah
> 

As far as I know, if there are any bits you can handle and ack, do so
and return IRQ_HANDLED. Otherwise, return IRQ_NONE. If there are still
pending bits, the interrupt will fire again, your handler will be called
again, return IRQ_NONE, and the next handler will be called.
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