Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <CAHp75Veo30c0BWb4Fykgvd-czSnEXsyA8wyMTeKQdS49=e5-nw@mail.gmail.com>
 <20220417165208.39754-1-schspa@gmail.com> <CAHp75Vc8HwheQVOpcn_Lxk-bOOMLybr=m6OdO7mJ-vE9xywBLg@mail.gmail.com>
 <CAMA88Tr6NvfEiPYnt0A60GiQKiiT6LT7X83GRku-4PDcG2EtoA@mail.gmail.com> <CAHp75VfcxACmuw5pwPgSB9ud06hWtHCUrMifU1rZJ+h+dwG+bg@mail.gmail.com>
In-Reply-To: <CAHp75VfcxACmuw5pwPgSB9ud06hWtHCUrMifU1rZJ+h+dwG+bg@mail.gmail.com>
From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Mon, 18 Apr 2022 14:39:56 +0300
Message-ID: <CAHp75Vchpi0Cvkz5krA0LEZBj-fQTXxbEBzpKxU96mcDRGY--A@mail.gmail.com>
Subject: Re: [PATCH] gpio: use raw spinlock for gpio chip shadowed data
To:     Schspa Shi <schspa@gmail.com>
Cc:     "brgl@bgdev.pl" <brgl@bgdev.pl>,
        "f.fainelli@gmail.com" <f.fainelli@gmail.com>,
        "fancer.lancer@gmail.com" <fancer.lancer@gmail.com>,
        "hoan@os.amperecomputing.com" <hoan@os.amperecomputing.com>,
        "linus.walleij@linaro.org" <linus.walleij@linaro.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-gpio@vger.kernel.org" <linux-gpio@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "opendmb@gmail.com" <opendmb@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Mon, Apr 18, 2022 at 2:38 PM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:
> On Mon, Apr 18, 2022 at 6:07 AM Schspa Shi <schspa@gmail.com> wrote:
> > Andy Shevchenko <andy.shevchenko@gmail.com> writes:
>
> ...
>
> > >   drivers/gpio/gpio-mmio.c    | 22 +++++++++++-----------
> > >   include/linux/gpio/driver.h |  2 +-
> > >
> > > You can=E2=80=99t do it for one driver only. As I told it will requir=
e 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.


--=20
With Best Regards,
Andy Shevchenko