linux-kernel - Re: [PATCH 0/7] gpio: mockup: extensions for testing purposes

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Date:   Tue, 31 Jan 2017 15:11:56 +0100
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linus Walleij <linus.walleij@...aro.org>
Cc:     Alexandre Courbot <gnurou@...il.com>,
        Bamvor Jian Zhang <bamvor.zhangjian@...aro.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/7] gpio: mockup: extensions for testing purposes

On 01/31/2017 03:05 PM, Bartosz Golaszewski wrote:
> 2017-01-31 14:28 GMT+01:00 Linus Walleij <linus.walleij@...aro.org>:
>> On Wed, Jan 25, 2017 at 4:34 PM, Bartosz Golaszewski
>> <bgolaszewski@...libre.com> wrote:
>>
>>> This series proposes to extend the gpio framework by allowing to
>>> inject line events from the kernel code and by providing a debugfs
>>> interface for that to the gpio-mockup driver. We also allow the
>>> user to request that the mockup driver name the lines.
>>
>> I sympathize fully with the goal and intentions of the series, I
>> agree: this is awesome to have for testing and validation of
>> GPIO.
>>
>> I'm reluctant about the changes to gpiolib and want to make that
>> code as optional as possible, definately #ifdef if nothing else
>> works. Otherwise the memory footprint people will get me for this,
>> haha. ;)
>>
>> The absolutely best would be if the driver could inject "real"
>> irqs and also exercise the gpiolib irqchip helpers. I have been
>> vaguely thinking that sofware interrupts should be able to do this
>> but I'm not very versed in that kind of stuff.
>>
> 
> This was my initial idea, but I thought it's not very likely that
> Thomas Gleixner would allow me to allocate a new software interrupt
> just for the sake of testing gpiolib. Also: the handling of softirqs
> seems to be a bit different than regular IRQs, but I'm too not an
> expert.

FWIW, we also need this in IIO. We currently inject our software IRQs for
testing using irq_work and handle_simple_irq()[1]. This has the advantage
that it goes the normal route through the IRQ subsystem and is even running
in IRQ context rather than application context (which is what happens if you
emulate the IRQ directly from the sysfs/debugfs callbacks).

- Lars

[1] http://lxr.free-electrons.com/source/drivers/iio/dummy/iio_dummy_evgen.c#L84