linux-kernel - Re: [PATCH v2 1/3] genirq: Allow the irqchip state of an IRQ to be save/restored

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Message-ID: <5486C2D6.6020006@arm.com>
Date:	Tue, 09 Dec 2014 09:37:26 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Bjorn Andersson <bjorn@...o.se>
CC:	Abhijeet Dharmapurikar <adharmap@...eaurora.org>,
	Stephen Boyd <sboyd@...eaurora.org>, Phong Vo <pvo@....com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Tin Huynh <tnhuynh@....com>, Y Vo <yvo@....com>,
	Thomas Gleixner <tglx@...utronix.de>, Toan Le <toanle@....com>,
	Jason Cooper <jason@...edaemon.net>,
	Arnd Bergmann <arnd@...db.de>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 1/3] genirq: Allow the irqchip state of an IRQ to be
 save/restored

On 08/12/14 22:42, Bjorn Andersson wrote:
> On Wed, Dec 3, 2014 at 8:18 AM, Marc Zyngier <marc.zyngier@....com> wrote:
>> There is a number of cases where a kernel subsystem may want to
>> introspect the state of an interrupt at the irqchip level:
>>
>> - When a peripheral is shared between virtual machines,
>>   its interrupt state becomes part of the guest's state,
>>   and must be switched accordingly. KVM on arm/arm64 requires
>>   this for its guest-visible timer
>> - Some GPIO controllers seem to require peeking into the
>>   interrupt controller they are connected to to report
>>   their internal state
>>
>> This seem to be a pattern that is common enough for the core code
>> to try and support this without too many horrible hacks. Introduce
>> a pair of accessors (irq_get_irqchip_state/irq_set_irqchip_state)
>> to retrieve the bits that can be of interest to another subsystem:
>> pending, active, and masked.
>>
>> - irq_get_irqchip_state returns the state of the interrupt according
>>   to a parameter set to IRQCHIP_STATE_PENDING, IRQCHIP_STATE_ACTIVE,
>>   IRQCHIP_STATE_MASKED or IRQCHIP_STATE_LINE_LEVEL.
>> - irq_set_irqchip_state similarly sets the state of the interrupt.
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> 
> With the addition of actually assigning err to something useful in the
> setter below:
> 
> Reviewed-by: Bjorn Andersson <bjorn.andersson@...ymobile.com>
> Tested-by: Bjorn Andersson <bjorn.andersson@...ymobile.com>
> 
>> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> 
> [..]
> 
>> +/**
>> + *     irq_set_irqchip_state - set the state of a forwarded interrupt.
>> + *     @irq: Interrupt line that is forwarded to a VM
>> + *     @which: State to be restored (one of IRQCHIP_STATE_*)
>> + *     @val: Value corresponding to @which
>> + *
>> + *     This call sets the internal irqchip state of an interrupt,
>> + *     depending on the value of @which.
>> + *
>> + *     This function should be called with preemption disabled if the
>> + *     interrupt controller has per-cpu registers.
>> + */
>> +int irq_set_irqchip_state(unsigned int irq, enum irqchip_irq_state which,
>> +                         bool val)
>> +{
>> +       struct irq_desc *desc;
>> +       struct irq_data *data;
>> +       struct irq_chip *chip;
>> +       unsigned long flags;
>> +       int err = -EINVAL;
>> +
>> +       desc = irq_get_desc_buslock(irq, &flags, 0);
>> +       if (!desc)
>> +               return err;
>> +
>> +       data = irq_desc_get_irq_data(desc);
>> +
>> +       do {
>> +               chip = irq_data_get_irq_chip(data);
>> +               if (chip->irq_set_irqchip_state)
>> +                       break;
>> +#ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
>> +               data = data->parent_data;
>> +#else
>> +               data = NULL;
>> +#endif
>> +       } while (data);
>> +
>> +       if (data)
>> +               chip->irq_set_irqchip_state(data, which, val);
> 
> err =

Ah, that will teach me to write test code that actually checks the
return value! :-)

Thanks for the fix and the tags.

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