linux-kernel - Re: [PATCH V6 2/9] genirq: Look-up trigger type if not specified by caller

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Message-ID: <575EA603.7090002@nvidia.com>
Date:	Mon, 13 Jun 2016 13:24:35 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Marc Zyngier <marc.zyngier@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>
CC:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Kevin Hilman <khilman@...nel.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Linus Walleij <linus.walleij@...aro.org>,
	<linux-tegra@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V6 2/9] genirq: Look-up trigger type if not specified by
 caller


On 13/06/16 12:59, Marc Zyngier wrote:
> On 13/06/16 12:09, Jon Hunter wrote:
>>
>> On 13/06/16 11:42, Marc Zyngier wrote:
>>> On 07/06/16 16:12, Jon Hunter wrote:
>>>> For some devices the IRQ trigger type for a device is read from
>>>> firmware, such as device-tree. The IRQ trigger type is typically read
>>>> when the mapping for IRQ is created, which is before the IRQ is
>>>> requested. Hence, the IRQ trigger type is programmed when mapping the
>>>> IRQ and not when requesting the IRQ.
>>>>
>>>> Although this works for most cases, in order to support IRQ chips which
>>>> require runtime power management, which may not be accessible prior
>>>> to requesting the IRQ, it is desirable to look-up the IRQ trigger type
>>>> when it is requested. Therefore, if the IRQ trigger type is not
>>>> specified when __setup_irq() is called, look-up the saved IRQ trigger
>>>> type. This will allow us to defer the programming of the trigger type
>>>> from when the IRQ is mapped to when it is actually requested.
>>>>
>>>> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
>>>> Reviewed-by: Marc Zyngier <marc.zyngier@....com>
>>>> ---
>>>>  kernel/irq/manage.c | 7 +++++++
>>>>  1 file changed, 7 insertions(+)
>>>>
>>>> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
>>>> index ef0bc02c3a70..eaedeb74b49d 100644
>>>> --- a/kernel/irq/manage.c
>>>> +++ b/kernel/irq/manage.c
>>>> @@ -1117,6 +1117,13 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
>>>>  	new->irq = irq;
>>>>  
>>>>  	/*
>>>> +	 * If the trigger type is not specified by the caller,
>>>> +	 * then use the default for this interrupt.
>>>> +	 */
>>>> +	if (!(new->flags & IRQF_TRIGGER_MASK))
>>>> +		new->flags |= irqd_get_trigger_type(&desc->irq_data);
>>>> +
>>>> +	/*
>>>>  	 * Check whether the interrupt nests into another interrupt
>>>>  	 * thread.
>>>>  	 */
>>>>
>>>
>>> I've added the following patch to the queue, in order to deal with
>>> percpu interrupts that were not handled by this patch:
>>>
>>> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
>>> index f8fd1fb..00cfc85 100644
>>> --- a/kernel/irq/manage.c
>>> +++ b/kernel/irq/manage.c
>>> @@ -1751,7 +1751,14 @@ void enable_percpu_irq(unsigned int irq, unsigned int type)
>>>  	if (!desc)
>>>  		return;
>>>  
>>> +	/*
>>> +	 * If the trigger type is not specified by the caller, then
>>> +	 * use the default for this interrupt.
>>> +	 */
>>>  	type &= IRQ_TYPE_SENSE_MASK;
>>> +	if (type == IRQ_TYPE_NONE)
>>> +		type = irqd_get_trigger_type(&desc->irq_data);
>>> +
>>
>> I am wondering if you need this here because now __setup_irq(), called
>> by request_percpu_irq(), will actually look-up the saved type even for a
>> percpu-irq. So shouldn't this already be handled? Or am I missing something?
> 
> You are overlooking the fact that the configuration registers are
> themselves per-CPU, which means that __setup_irq() will only configure
> the interrupt on the CPU it runs on. And you can't even tell which one,
> since you are in a preemptible context.
> 
> Does it make more sense?

Yes it does thanks. I am guessing we don't need to worry about there
being different type configurations for the different CPUs for a given
interrupt?

Cheers
Jon

-- 
nvpublic