linux-kernel - RE: [PATCH v9 5/6] usb:cdns3 Add Cadence USB3 DRD Driver

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Message-ID: <BYAPR07MB4709648F659AB5A11B0EB621DDF10@BYAPR07MB4709.namprd07.prod.outlook.com>
Date:   Tue, 9 Jul 2019 07:29:10 +0000
From:   Pawel Laszczak <pawell@...ence.com>
To:     Felipe Balbi <felipe.balbi@...ux.intel.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "hdegoede@...hat.com" <hdegoede@...hat.com>,
        "heikki.krogerus@...ux.intel.com" <heikki.krogerus@...ux.intel.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "rogerq@...com" <rogerq@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jbergsagel@...com" <jbergsagel@...com>,
        "nsekhar@...com" <nsekhar@...com>, "nm@...com" <nm@...com>,
        Suresh Punnoose <sureshp@...ence.com>,
        "peter.chen@....com" <peter.chen@....com>,
        Jayshri Dajiram Pawar <jpawar@...ence.com>,
        Rahul Kumar <kurahul@...ence.com>
Subject: RE: [PATCH v9 5/6] usb:cdns3 Add Cadence USB3 DRD Driver

>
>
>Hi,
>
>Pawel Laszczak <pawell@...ence.com> writes:
>>>>>> IRQF_ONESHOT can be used  only in threaded handled.
>>>>>> "
>>>>>>  * IRQF_ONESHOT - Interrupt is not reenabled after the hardirq handler finished.
>>>>>>  *                Used by threaded interrupts which need to keep the
>>>>>>  *                irq line disabled until the threaded handler has been run.
>>>>>> "
>>>>>
>>>>>so?
>>>>
>>>> I don't understand why If I don't have threaded handler why I need IRQF_ONESHOT.
>>>> Why interrupt cannot be reenabled after hardirq handler finished ?
>>>> I do not use threaded handler so this flag seem unnecessary.
>>>
>>>Unless this has changed over the years, it was a requirement from IRQ susbystem.
>>>
>>>	/*
>>>	 * Drivers are often written to work w/o knowledge about the
>>>	 * underlying irq chip implementation, so a request for a
>>>	 * threaded irq without a primary hard irq context handler
>>>	 * requires the ONESHOT flag to be set. Some irq chips like
>>>	 * MSI based interrupts are per se one shot safe. Check the
>>>	 * chip flags, so we can avoid the unmask dance at the end of
>>>	 * the threaded handler for those.
>>>	 */
>>>	if (desc->irq_data.chip->flags & IRQCHIP_ONESHOT_SAFE)
>>>		new->flags &= ~IRQF_ONESHOT;
>>
>> From description I understand that it should be set when driver uses only
>> threaded handler without hard irq handler.
>> eg.
>>
>> 	ret = devm_request_threaded_irq(dev, data->usb_id_irq,
>> 					NULL, int3496_thread_isr,
>> 					IRQF_SHARED | IRQF_ONESHOT |
>> 					IRQF_TRIGGER_RISING |
>> 					IRQF_TRIGGER_FALLING,
>> 					dev_name(dev), data);
>>
>> It make sense, we don't have hard irq handler so we can't clear source of interrupt.
>> If we clear it immediately in interrupt controller then the same interrupt could
>> be raised again, because it was not cleared e.g in controller register.
>
>You are correct. Big mistake on my side. Apologies.

All right, you're welcome. I learn a lot of during such discussions :).

>--
>balbi