Re: [PATCH v1] gpio: mmio: restroe get multiple gpio mask

[Yan Wang]

On 4/24/2023 2:56 PM, Linus Walleij wrote:
> Hi Yan,
>
> thanks for your patch!
>
> On Sun, Apr 23, 2023 at 11:07 AM Yan Wang <rk.code@xxxxxxxxxxx> wrote:
>
> > Simplify the code,should not modify its logic.
> I don't see how it simplifies the code, it seems to me that it is
> making it more complex?
yes ,it is .
The description is wrong.
> > Fixes: 761b5c30c206 ("gpio: mmio: replace open-coded for_each_set_bit()")
> > Signed-off-by: Yan Wang <rk.code@xxxxxxxxxxx>
> > ---
> >   drivers/gpio/gpio-mmio.c | 12 ++++++++----
> >   1 file changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpio/gpio-mmio.c b/drivers/gpio/gpio-mmio.c
> > index d9dff3dc92ae..c2347ef3a4df 100644
> > --- a/drivers/gpio/gpio-mmio.c
> > +++ b/drivers/gpio/gpio-mmio.c
> > @@ -271,10 +271,14 @@ static void bgpio_multiple_get_masks(struct gpio_chip *gc,
> >          *clear_mask = 0;
> >
> >          for_each_set_bit(i, mask, gc->bgpio_bits) {
> > -               if (test_bit(i, bits))
> > -                       *set_mask |= bgpio_line2mask(gc, i);
> > -               else
> > -                       *clear_mask |= bgpio_line2mask(gc, i);
> > +               if (*mask == 0)
> > +                       break;
> > +               if (__test_and_clear_bit(i, mask)) {
> > +                       if (test_bit(i, bits))
> > +                               *set_mask |= bgpio_line2mask(gc, i);
> > +                       else
> > +                               *clear_mask |= bgpio_line2mask(gc, i);
> > +               }
> The intention of the change seems to be to break out of the loop
> when all set bits are handled, by successively masking off one
> bit at a time from mask. So this is intended as an optimization,
> not a simplification.
Because my description is wrong and there is a difference in 
understanding between us.
I think using for_each_set_bit() , but the __test_and_clear_bit() should 
not remove.
> I think for_each_set_bit() is already skipping over every bit
> that is zero, see include/linux/find.h.
>
> So this optimization gains us nothing.
this a patch that only restores to original logic.the 
__test_and_clear_bit() clear mask
then get a new set_mask. this logic can affect functions of 
gpiod_set_raw_array_value ().

The effect of this patch is as follows:
gpiod_set_raw_array_value->
    gpiod_set_array_value_complex->
{
    ..
    if (array_info && array_info->desc == desc_array &&
        array_size <= array_info->size &&
        (void *)array_info == desc_array + array_info->size) {
        if (!can_sleep)
            WARN_ON(array_info->chip->can_sleep);

        if (!raw && !bitmap_empty(array_info->invert_mask, array_size))
            bitmap_xor(value_bitmap, value_bitmap,
                   array_info->invert_mask, array_size);

        gpio_chip_set_multiple(array_info->chip, array_info->set_mask,
                       value_bitmap);

        i = find_first_zero_bit(array_info->set_mask, array_size);
        if (i == array_size)
            return 0;
    } else {
        array_info = NULL;
    }

   -> while (i < array_size) {
        struct gpio_chip *gc = desc_array[i]->gdev->chip;
        DECLARE_BITMAP(fastpath_mask, FASTPATH_NGPIO);
        DECLARE_BITMAP(fastpath_bits, FASTPATH_NGPIO);
        unsigned long *mask, *bits;
        int count = 0;

         ..............
        if (count != 0)
            gpio_chip_set_multiple(gc, mask, bits);

        ..............
    }
    return 0;
}

Due to __test_and_clear_bit() clear array_info->set_mask,the i < 
array_size condition holds.
then calculate a new mask based on the GPIO number of the hardware.

I reconfirmed it,Although it works, it should not be modified in the place.
I think have a wrong of gpiod_get_array() and not 
bgpio_multiple_get_masks().

Link: 
https://lore.kernel.org/linux-gpio/KL1PR01MB5448327326B6EDA8001AF714E6669@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/

this is a new patch. can you take a look ?

Thank you.
> Yours,
> Linus Walleij