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Message-ID: <TY0PR01MB5444D02ECB86488FDB9C6B6AE6679@TY0PR01MB5444.apcprd01.prod.exchangelabs.com>
Date: Mon, 24 Apr 2023 17:03:33 +0800
From: Yan Wang <rk.code@...look.com>
To: Linus Walleij <linus.walleij@...aro.org>
Cc: brgl@...ev.pl, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
"open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] gpio: mmio: restroe get multiple gpio mask
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@...look.com> 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@...look.com>
>> ---
>> 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@KL1PR01MB5448.apcprd01.prod.exchangelabs.com/
this is a new patch. can you take a look ?
Thank you.
> Yours,
> Linus Walleij
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