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

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Date:   Tue, 09 Jul 2019 10:22:40 +0300
From:   Felipe Balbi <felipe.balbi@...ux.intel.com>
To:     Pawel Laszczak <pawell@...ence.com>,
        "devicetree\@vger.kernel.org" <devicetree@...r.kernel.org>
Cc:     "gregkh\@linuxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb\@vger.kernel.org" <linux-usb@...r.kernel.org>,
        "hdegoede\@redhat.com" <hdegoede@...hat.com>,
        "heikki.krogerus\@linux.intel.com" <heikki.krogerus@...ux.intel.com>,
        "robh+dt\@kernel.org" <robh+dt@...nel.org>,
        "rogerq\@ti.com" <rogerq@...com>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "jbergsagel\@ti.com" <jbergsagel@...com>,
        "nsekhar\@ti.com" <nsekhar@...com>, "nm\@ti.com" <nm@...com>,
        Suresh Punnoose <sureshp@...ence.com>,
        "peter.chen\@nxp.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.

-- 
balbi