Re: [PATCH] gpiolib: Fix incorrect use of find_next_zero_bit()

Marek Szyprowski
2018-10-01T06:46:28Z

Hi Janusz,

On 2018-09-29 14:20, Janusz Krzysztofik wrote:
> Commit b17566a6b08b ("gpiolib: Implement fast processing path in
> get/set array"), already fixed to some extent with commit 5d581d7e8cdc
> ("gpiolib: Fix missing updates of bitmap index"), introduced a new mode
> of processing bitmaps where bits applicable for fast bitmap processing
> path are supposed to be skipped while iterating bits which don't apply.
> Unfortunately, find_next_zero_bit() function supposed to skip over
> those fast bits is always called with a 'start' argument equal to an
> index of last zero bit found and returns that index value again an
> again, causing an infinite loop.
>
> Fix it by incrementing the index uncoditionally before
> find_next_zero_bit() is optionally called.
>
> Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>

> ---
> Marek,
>
> Could you please test it on top of next-20180920 with "gpiolib: Fix
> missing updates of bitmap index" and optionally "mmc: pwrseq_simple:
> Fix incorrect handling of GPIO bitmap" also applied?

This patch finally fixes the boot issue on Samsung Chromebook Snow.
Thanks!

>
> Thanks,
> Janusz
>
>
> drivers/gpio/gpiolib.c | 9 +++------
> 1 file changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 6ae13e3e05f1..940b543e966d 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -2878,12 +2878,11 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep,
> int hwgpio = gpio_chip_hwgpio(desc);
>
> __set_bit(hwgpio, mask);
> + i++;
>
> if (array_info)
> i = find_next_zero_bit(array_info->get_mask,
> array_size, i);
> - else
> - i++;
> } while ((i < array_size) &&
> (desc_array[i]->gdev->chip == chip));
>
> @@ -2903,12 +2902,11 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep,
> value = !value;
> __assign_bit(j, value_bitmap, value);
> trace_gpio_value(desc_to_gpio(desc), 1, value);
> + j++;
>
> if (array_info)
> j = find_next_zero_bit(array_info->get_mask, i,
> j);
> - else
> - j++;
> }
>
> if (mask != fastpath)
> @@ -3191,12 +3189,11 @@ int gpiod_set_array_value_complex(bool raw, bool can_sleep,
> __clear_bit(hwgpio, bits);
> count++;
> }
> + i++;
>
> if (array_info)
> i = find_next_zero_bit(array_info->set_mask,
> array_size, i);
> - else
> - i++;
> } while ((i < array_size) &&
> (desc_array[i]->gdev->chip == chip));
> /* push collected bits to outputs */

Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland