linux-kernel - Re: [PATCH] gpiolib: Fix incorrect use of find_next_zero

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Date:   Mon, 1 Oct 2018 08:46:16 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Janusz Krzysztofik <jmkrzyszt@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>
Cc:     Miguel Ojeda Sandonis <miguel.ojeda.sandonis@...il.com>,
        Peter Korsgaard <peter.korsgaard@...co.com>,
        Peter Rosin <peda@...ntia.se>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Jiri Slaby <jslaby@...e.com>, Willy Tarreau <w@....eu>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Sebastien Bourdelin <sebastien.bourdelin@...oirfairelinux.com>,
        Lukas Wunner <lukas@...ner.de>,
        Rojhalat Ibrahim <imr@...chenk.de>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Tony Lindgren <tony@...mide.com>,
        Yegor Yefremov <yegorslists@...glemail.com>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linux-gpio@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-mmc@...r.kernel.org, netdev@...r.kernel.org,
        linux-iio@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-serial@...r.kernel.org,
        Linux Samsung SOC <linux-samsung-soc@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gpiolib: Fix incorrect use of find_next_zero_bit()

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@...sung.com>
> Signed-off-by: Janusz Krzysztofik <jmkrzyszt@...il.com>

Tested-by: Marek Szyprowski <m.szyprowski@...sung.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