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

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Message-ID: <CAMpxmJUfNkko4Rrb4N5CF_rdwRAWGhVr9DSOHfhYyTxYSH7dsQ@mail.gmail.com>
Date:   Mon, 7 Sep 2020 14:06:15 +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 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? Should we
keep some backwards compatibility? Should we introduce an entirely new
module and have a transition period before removing previous
gpio-mockup?

Also: this is a testing module so to me debugfs is just fine. Is
configfs considered stable ABI like sysfs?

Bart