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

[Andy Shevchenko]

On Mon, Sep 07, 2020 at 02:57:29PM +0200, Bartosz Golaszewski wrote:
> On Mon, Sep 7, 2020 at 2:38 PM Andy Shevchenko
> <andriy.shevchenko@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx> 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.

When I wrote above I didn't mean this should be done in a hurry. Just during
one release to make all parties ready for the change.

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

Sure!

-- 
With Best Regards,
Andy Shevchenko