linux-kernel - Re: [PATCH] gpio: use raw spinlock for gpio chip shadowed data

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Message-ID: <CAHp75Vchpi0Cvkz5krA0LEZBj-fQTXxbEBzpKxU96mcDRGY--A@mail.gmail.com>
Date:   Mon, 18 Apr 2022 14:39:56 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Schspa Shi <schspa@...il.com>
Cc:     "brgl@...ev.pl" <brgl@...ev.pl>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "fancer.lancer@...il.com" <fancer.lancer@...il.com>,
        "hoan@...amperecomputing.com" <hoan@...amperecomputing.com>,
        "linus.walleij@...aro.org" <linus.walleij@...aro.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "opendmb@...il.com" <opendmb@...il.com>
Subject: Re: [PATCH] gpio: use raw spinlock for gpio chip shadowed data

On Mon, Apr 18, 2022 at 2:38 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> On Mon, Apr 18, 2022 at 6:07 AM Schspa Shi <schspa@...il.com> wrote:
> > Andy Shevchenko <andy.shevchenko@...il.com> writes:
>
> ...
>
> > >   drivers/gpio/gpio-mmio.c    | 22 +++++++++++-----------
> > >   include/linux/gpio/driver.h |  2 +-
> > >
> > > You can’t do it for one driver only. As I told it will require too much of additional churn to make this to be series.
> > >
> >
> > It seems I have misunderstood your "too much of additional churn". Can
> > you explain it?
> > The gpio-mmio.c and driver.h here are the basics of other gpio
> > drivers. In my opinion, these two files
> > belong to the basic code of gpio, and functions such as bgpio_init are
> > declared in
> > include/linux/gpio/driver.h and implemented in
> > drivers/gpio/gpio-mmio.c. So there is no churn.
>
> When you change the member of the data structure, you have to change
> all its users. You can't change only one at a time because it will be
> a (compile-time) bisectability issue.

Answering your question here, it will require moving to union with an
additional member and corresponding core changes, convert all drivers
one-by-one, and remove the old type. It's not worth doing it, but as I
said let maintainers decide.


-- 
With Best Regards,
Andy Shevchenko