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

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Message-ID: <20200907123837.GG1891694@smile.fi.intel.com>
Date:   Mon, 7 Sep 2020 15:38:37 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <bgolaszewski@...libre.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 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.

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

But this one is a good question. I think ConfigFS is stricter than DebugFS,
up to being an ABI. But never did myself such a thing, so would like to hear
experienced developers.

-- 
With Best Regards,
Andy Shevchenko