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

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Message-ID: <575EA03D.5070706@arm.com>
Date:	Mon, 13 Jun 2016 12:59:57 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Jon Hunter <jonathanh@...dia.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 12:09, 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?

	M.
-- 
Jazz is not dead. It just smells funny...