linux-kernel - Re: [PATCH v3 3/3] gpio: xilinx: Utilize generic bitmap_get_value and _set

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Date:   Fri, 2 Apr 2021 15:10:37 +0530
From:   Syed Nayyar Waris <syednwaris@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        William Breathitt Gray <vilhelm.gray@...il.com>,
        Michal Simek <michal.simek@...inx.com>,
        Arnd Bergmann <arnd@...db.de>,
        Robert Richter <rrichter@...vell.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Zhang, Rui" <rui.zhang@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Amit Kucheria <amit.kucheria@...durent.com>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] gpio: xilinx: Utilize generic bitmap_get_value and _set_value

On Fri, Mar 26, 2021 at 11:27 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
> On Sat, Mar 6, 2021 at 4:08 PM Syed Nayyar Waris <syednwaris@...il.com> wrote:
> >
> > This patch reimplements the xgpio_set_multiple() function in
> > drivers/gpio/gpio-xilinx.c to use the new generic functions:
> > bitmap_get_value() and bitmap_set_value(). The code is now simpler
> > to read and understand. Moreover, instead of looping for each bit
> > in xgpio_set_multiple() function, now we can check each channel at
> > a time and save cycles.
>
> ...
>
> > +       u32 *const state = chip->gpio_state;
> > +       unsigned int *const width = chip->gpio_width;
>
> > +
>
> Extra blank line.
>
> > +       DECLARE_BITMAP(old, 64);
> > +       DECLARE_BITMAP(new, 64);
> > +       DECLARE_BITMAP(changed, 64);
>
> > +       spin_lock_irqsave(&chip->gpio_lock[0], flags);
> > +       spin_lock(&chip->gpio_lock[1]);
>
> I understand why this is done at the top of the function in the original code.
> I do not understand why you put some operations under spin lock.
>
> Have you checked what each of these spin locks protects?
> Please check and try to lock as minimum as possible.
>
> > +       bitmap_set_value(old, 64, state[0], width[0], 0);
> > +       bitmap_set_value(old, 64, state[1], width[1], width[0]);
> > +       bitmap_replace(new, old, bits, mask, gc->ngpio);
> > +
> > +       bitmap_set_value(old, 64, state[0], 32, 0);
> > +       bitmap_set_value(old, 64, state[1], 32, 32);
> > +       state[0] = bitmap_get_value(new, 0, width[0]);
> > +       state[1] = bitmap_get_value(new, width[0], width[1]);
> > +       bitmap_set_value(new, 64, state[0], 32, 0);
> > +       bitmap_set_value(new, 64, state[1], 32, 32);
> > +       bitmap_xor(changed, old, new, 64);
>
> Original code and this is cryptic. Can you add a few comments
> explaining what is going on here?
>
> > +       spin_unlock(&chip->gpio_lock[1]);
> > +       spin_unlock_irqrestore(&chip->gpio_lock[0], flags);
>
> --
> With Best Regards,
> Andy Shevchenko

Have removed the extra line and added comments. Regarding locking - I
see that now there is just a single lock available instead of 2 locks.
Have made necessary changes. Thanks
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/gpio/gpio-xilinx.c?id=37ef334680800263b32bb96a5156a4b47f0244a2

Regards

Syed Nayyar Waris