Re: [PATCH] gpio: Add missing open drain/source handling to gpiod_set_value_cansleep()

["Jan Kundrát" <jan.kundrat@cesnet.cz>]

On úterý 9. ledna 2018 19:08:21 CET, Geert Uytterhoeven wrote:
> Since commit f11a04464ae57e8d ("i2c: gpio: Enable working over slow
> can_sleep GPIOs"), probing the i2c RTC connected to an i2c-gpio bus on
> r8a7740/armadillo fails with:
>
>     rtc-s35390a 0-0030: error resetting chip
>     rtc-s35390a: probe of 0-0030 failed with error -5
>
> More debug code reveals:
>
>     i2c i2c-0: master_xfer[0] R, addr=0x30, len=1
>     i2c i2c-0: NAK from device addr 0x30 msg #0
>     s35390a_get_reg: ret = -6
>
> Commit 02e479808b5d62f8 ("gpio: Alter semantics of *raw* operations to
> actually be raw") moved open drain/source handling from
> gpiod_set_raw_value_commit() to gpiod_set_value(), but forgot to take
> into account that gpiod_set_value_cansleep() also needs this handling.
> The i2c protocol mandates that i2c signals are open drain, hence i2c
> communication fails.
>
> Fix this by adding the missing handling to gpiod_set_value_cansleep(),
> using a new common helper __gpiod_set_value_nocheck().
>
> Fixes: 02e479808b5d62f8 ("gpio: Alter semantics of *raw* 
> operations to actually be raw")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
> The bad gpio commit is in v4.15-rc1 and later.
> The i2c commit exposing this is not yet upstream, but in i2c/for-next.
> ---
>  drivers/gpio/gpiolib.c | 26 ++++++++++++++------------
>  1 file changed, 14 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 358bce6e798b476c..7761d632a5b0dd20 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -2927,6 +2927,18 @@ void gpiod_set_raw_value(struct 
> gpio_desc *desc, int value)
>  }
>  EXPORT_SYMBOL_GPL(gpiod_set_raw_value);
>  
> +static void __gpiod_set_value_nocheck(struct gpio_desc *desc, int value)
> +{
> +	if (test_bit(FLAG_ACTIVE_LOW, &desc->flags))
> +		value = !value;
> +	if (test_bit(FLAG_OPEN_DRAIN, &desc->flags))
> +		gpio_set_open_drain_value_commit(desc, value);
> +	else if (test_bit(FLAG_OPEN_SOURCE, &desc->flags))
> +		gpio_set_open_source_value_commit(desc, value);
> +	else
> +		gpiod_set_raw_value_commit(desc, value);
> +}
> +
>  /**
>   * gpiod_set_value() - assign a gpio's value
>   * @desc: gpio whose value will be assigned
> @@ -2941,16 +2953,8 @@ EXPORT_SYMBOL_GPL(gpiod_set_raw_value);
>  void gpiod_set_value(struct gpio_desc *desc, int value)
>  {
>  	VALIDATE_DESC_VOID(desc);
> -	/* Should be using gpiod_set_value_cansleep() */
>  	WARN_ON(desc->gdev->chip->can_sleep);
> -	if (test_bit(FLAG_ACTIVE_LOW, &desc->flags))
> -		value = !value;
> -	if (test_bit(FLAG_OPEN_DRAIN, &desc->flags))
> -		gpio_set_open_drain_value_commit(desc, value);
> -	else if (test_bit(FLAG_OPEN_SOURCE, &desc->flags))
> -		gpio_set_open_source_value_commit(desc, value);
> -	else
> -		gpiod_set_raw_value_commit(desc, value);
> +	__gpiod_set_value_nocheck(desc, value);
>  }
>  EXPORT_SYMBOL_GPL(gpiod_set_value);
>  
> @@ -3277,9 +3281,7 @@ void gpiod_set_value_cansleep(struct 
> gpio_desc *desc, int value)
>  {
>  	might_sleep_if(extra_checks);
>  	VALIDATE_DESC_VOID(desc);
> -	if (test_bit(FLAG_ACTIVE_LOW, &desc->flags))
> -		value = !value;
> -	gpiod_set_raw_value_commit(desc, value);
> +	__gpiod_set_value_nocheck(desc, value);
>  }
>  EXPORT_SYMBOL_GPL(gpiod_set_value_cansleep);
>  

I realize that I'm late to the party (a merge request has been sent), but I 
can confirm that I tested that this still works for a bitbang I2C over GPIO 
pins connected to MAX14830 managed by max310x.

Tested-By: Jan Kundrát <jan.kundrat@cesnet.cz>

Cheers,
Jan