linux-kernel - Re: [PATCH 1/2] extcon: extcon-dra7xx: Add extcon driver for USB ID detection

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Date:	Wed, 21 Aug 2013 08:07:23 +0900
From:	Chanwoo Choi <cw00.choi@...sung.com>
To:	George Cherian <george.cherian@...com>
Cc:	balbi@...com, myungjoo.ham@...sung.com, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	grant.likely@...aro.org, rob@...dley.net, ian.campbell@...rix.com,
	swarren@...dotorg.org, mark.rutland@....com, pawel.moll@....com,
	rob.herring@...xeda.com, linux-omap@...r.kernel.org,
	linux-usb@...r.kernel.org, bcousson@...libre.com
Subject: Re: [PATCH 1/2] extcon: extcon-dra7xx: Add extcon driver for USB ID
 detection

>>>>> +
>>>>> +    if (dra7xx_usb->irq_gpio) {
>>>>> +        status = devm_request_threaded_irq(dra7xx_usb->dev, irq_num,
>>>>> +                NULL, id_irq_handler, IRQF_SHARED |
>>>>> +                IRQF_ONESHOT | IRQF_TRIGGER_FALLING,
>>>>> +                dev_name(&pdev->dev), (void *) dra7xx_usb);
>>>>> +        if (status)
>>>>> +            dev_err(dra7xx_usb->dev, "failed to request irq #%d\n",
>>>>> +                        irq_num);
>>>> If devm_request_threaded_irq() return fail state, why did not you do add error exception?
>>> If interrupt fails I fallback to polling thread.
>>>>> +        else
>>>>> +            return 0;
>>>> If devm_request_threaded_irq() return success state, why did you directly call 'return'?
>>>> kthread_create operation isn't necessary?
>>> Yes kthread is optional. Some boards doenot have the ID pin hooked onto the GPIO.
>>> In such cases we will run the kthread and poll on the ID pin values.
>>>>> +    }
>>>>> +
>>>>> +    dra7xx_usb->thread_task = kthread_create(id_poll_func, dra7xx_usb,
>>>>> +                         dev_name(&pdev->dev));
>>>> Should you use polling method with kthread? I think it isn't proper method.
>>>> You did get the irq number by using DT helper function and register irq handler
>>>> with devm_request_threaded_irq(). I prefer interrupt method for detection of cable state.
>>> I also prefer interrupt method. If any implementation does not have ID pin connected to GPIOs then still
>>> it could use the driver in polling mode.
>> As I mentioned above, I don't prefer interrupt method for cable detection.
> 
> I hope you meant, you prefer interrupt method for cable detection over polling .

Right, my mistake. I prefer interrupt method.

Thanks,
Chanwoo CHoi


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