Re: [PATCH v3 3/3] gpio: xilinx: Utilize generic bitmap_get_value and _set_value

[Syed Nayyar Waris <syednwaris@xxxxxxxxx>]

On Fri, Mar 26, 2021 at 11:27 PM Andy Shevchenko
<andy.shevchenko@xxxxxxxxx> wrote:
>
> On Sat, Mar 6, 2021 at 4:08 PM Syed Nayyar Waris <syednwaris@xxxxxxxxx> 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