linux-kernel - Re: [PATCH v2 09/12] gpio: sim: new testing module

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Date:   Fri, 5 Mar 2021 12:15:50 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Joel Becker <jlbec@...lplan.org>, Christoph Hellwig <hch@....de>,
        Shuah Khan <shuah@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Kent Gibson <warthog618@...il.com>,
        Jonathan Corbet <corbet@....net>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-doc <linux-doc@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH v2 09/12] gpio: sim: new testing module

On Thu, Mar 04, 2021 at 09:15:29PM +0100, Bartosz Golaszewski wrote:
> On Thu, Mar 4, 2021 at 2:15 PM Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
> > On Thu, Mar 04, 2021 at 11:24:49AM +0100, Bartosz Golaszewski wrote:
> > > From: Bartosz Golaszewski <bgolaszewski@...libre.com>

> > > +
> > > +     /*
> > > +      * FIXME If anyone knows a better way to parse that - please let me
> > > +      * know.
> > > +      */
> >
> > If comma can be replaced with ' ' (space) then why not to use next_arg() from
> > cmdline.c? I.o.w. do you have strong opinion why should we use comma here?
> >
> 
> My opinion is not very strong but I wanted to make the list of names
> resemble what we pass to the gpio-line-names property in device tree.
> Doesn't next_arg() react differently to string of the form: "foo=bar"?

It's ambiguous here.

So, the strings '"foo=bar"' and 'foo=bar' (w/o single quotes!) are indeed
parsed differently, i.e.
	'"foo=bar"' -> 'foo=bar',
while
	"foo=bar" -> 'foo' + 'bar'.

...

> > > +     ida_free(&gpio_sim_ida, id);
> >
> > Isn't it atomic per se? I mean that IDA won't give the same ID until you free
> > it. I.o.w. why is it under the mutex?
> >
> 
> You're right but if we rapidly create and destroy chips we'll be left
> with holes in the numbering (because new devices would be created
> before the IDA numbers are freed, so the driver would take a larger
> number that's currently free). It doesn't hurt but it would look worse
> IMO. Do you have a strong opinion on this?

It's not strong per se, but I would rather follow the 2nd rule of locking:
don't protect something which doesn't need it.

-- 
With Best Regards,
Andy Shevchenko