linux-kernel - Re: [PATCH 3/3] irq/irq_sim: implement irq_sim

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Date:   Wed, 18 Oct 2017 11:51:51 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] irq/irq_sim: implement irq_sim_irq2offset()

2017-10-18 10:58 GMT+02:00 Marc Zyngier <marc.zyngier@....com>:
> On 05/10/17 13:44, Bartosz Golaszewski wrote:
>> Add a routine allowing to retrieve the offset corresponding with an
>> allocated interrupt number from an irq_sim object.
>>
>> Signed-off-by: Bartosz Golaszewski <brgl@...ev.pl>
>> ---
>>  include/linux/irq_sim.h |  1 +
>>  kernel/irq/irq_sim.c    | 15 +++++++++++++++
>>  2 files changed, 16 insertions(+)
>>
>> diff --git a/include/linux/irq_sim.h b/include/linux/irq_sim.h
>> index 246f593face8..e9768ca81e3e 100644
>> --- a/include/linux/irq_sim.h
>> +++ b/include/linux/irq_sim.h
>> @@ -41,5 +41,6 @@ void irq_sim_fini(struct irq_sim *sim);
>>  void irq_sim_fire(struct irq_sim *sim, unsigned int offset);
>>  int irq_sim_irqnum(struct irq_sim *sim, unsigned int offset);
>>  int irq_sim_baseirq(struct irq_sim *sim);
>> +unsigned int irq_sim_irq2offset(struct irq_sim *sim, int irq);
>>
>>  #endif /* _LINUX_IRQ_SIM_H */
>> diff --git a/kernel/irq/irq_sim.c b/kernel/irq/irq_sim.c
>> index 1be10d0e295f..9a9a1bc8853c 100644
>> --- a/kernel/irq/irq_sim.c
>> +++ b/kernel/irq/irq_sim.c
>> @@ -174,3 +174,18 @@ int irq_sim_baseirq(struct irq_sim *sim)
>>       return irq_sim_irqnum(sim, 0);
>>  }
>>  EXPORT_SYMBOL_GPL(irq_sim_baseirq);
>> +
>> +/**
>> + * irq_sim_irq2offset - Get the offset of an allocated interrupt.
>> + *
>> + * @sim:        The interrupt simulator object.
>> + * irq:         Allocated interrupt number.
>> + *
>> + * Perform a reverse lookup for the interrupt number and return its offset in
>> + * the array allocated by sim_irq.
>> + */
>> +unsigned int irq_sim_irq2offset(struct irq_sim *sim, int irq)
>> +{
>> +     return irq - sim->irq_base;
>> +}
>> +EXPORT_SYMBOL_GPL(irq_sim_irq2offset);
>>
>
> How is that useful in a random driver? The irq base and the offset are
> things that should be internal to an irqchip. Maybe you could explain
> the context you want to use this in.
>

The interrupts are allocated within the interrupt simulator code, but
it's up to users to actually request these irqs. That's why we already
have sim_irq_irqnum().

The IIO dummy driver (one of the users of irq_sim) uses these irq
numbers retrieved from the simulator to also access private data
stored in the iio_dummy_evgen module. Currently we store the base
interrupt number in a separate variable in the dummy_evgen context
struct and calculate the offset in the interrupt array manually. We
could simplify that code by moving this logic into the interrupt
simulator.

I hope it's clear enough.

Best regards,
Bartosz Golaszewski