linux-kernel - Re: [PATCH 23/23] Documentation: gpio: add documentation for gpio-mockup

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Message-ID: <CAMpxmJXNYZb66SPuzR_3CEVwD=PQ6z6Ew3ia7ZL=wSU0QGhjEA@mail.gmail.com>
Date:   Mon, 7 Sep 2020 14:57:29 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Kent Gibson <warthog618@...il.com>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        linux-doc <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 23/23] Documentation: gpio: add documentation for gpio-mockup

On Mon, Sep 7, 2020 at 2:38 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Mon, Sep 07, 2020 at 02:06:15PM +0200, Bartosz Golaszewski wrote:
> > On Mon, Sep 7, 2020 at 1:53 PM Andy Shevchenko
> > <andriy.shevchenko@...ux.intel.com> wrote:
> > > On Mon, Sep 07, 2020 at 12:26:34PM +0200, Bartosz Golaszewski wrote:
> > > > On Mon, Sep 7, 2020 at 11:59 AM Andy Shevchenko
> > > > <andriy.shevchenko@...ux.intel.com> wrote:
> > > > > On Fri, Sep 04, 2020 at 08:15:59PM -0700, Randy Dunlap wrote:
> > > > > > On 9/4/20 8:45 AM, Bartosz Golaszewski wrote:
>
> ...
>
> > > > > > > +GPIO Testing Driver
> > > > > > > +===================
> > > > > > > +
> > > > > > > +The GPIO Testing Driver (gpio-mockup) provides a way to create simulated GPIO
> > > > > > > +chips for testing purposes. There are two ways of configuring the chips exposed
> > > > > > > +by the module. The lines can be accessed using the standard GPIO character
> > > > > > > +device interface as well as manipulated using the dedicated debugfs directory
> > > > > > > +structure.
> > > > > >
> > > > > > Could configfs be used for this instead of debugfs?
> > > > > > debugfs is ad hoc.
> > > > >
> > > > > Actually sounds like a good idea.
> > > > >
> > > >
> > > > Well, then we can go on and write an entirely new mockup driver
> > > > (ditching module params and dropping any backwards compatibility)
> > > > because we're already using debugfs for line values.
> > > >
> > > > How would we pass the device properties to configfs created GPIO chips
> > > > anyway? Devices seem to only be created using mkdir. Am I missing
> > > > something?
> > >
> > > Same way how USB composite works, no?
> > >
> >
> > OK, so create a new chip directory in configfs, configure it using
> > some defined configfs attributes and then finally instantiate it from
> > sysfs?
> >
> > Makes sense and is probably the right way to go. Now the question is:
> > is it fine to just entirely remove the previous gpio-mockup?
>
> Since, for example, I never saw device property bindings for that driver I
> assume that it was never considered as an ABI, so feel free to hack it in
> either direction.
>
> > Should we
> > keep some backwards compatibility?
>
> I wouldn't probably spend time on this.
>
> > Should we introduce an entirely new
> > module and have a transition period before removing previous
> > gpio-mockup?
>
> Neither transition period.
>

I wouldn't rush this actually. gpio-mockup is used a lot by libgpiod
and probably by Kent's Go library. My main goal with this series is to
extend it to allow for more advanced testing like simulating spurious
irqs to test the software debouncer or custom line name formats to
test name lookups.

I need to think about it some more. An entirely new configfs interface
would take time too.

Bart