linux-kernel - Re: [PATCH] gpio: Propagate errors from chip->get()

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Message-ID: <20150901051613.GE13472@usrtlx11787.corpusers.net>
Date:	Mon, 31 Aug 2015 22:16:13 -0700
From:	Bjorn Andersson <bjorn.andersson@...ymobile.com>
To:	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>
CC:	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpio: Propagate errors from chip->get()

On Fri 28 Aug 09:44 PDT 2015, Bjorn Andersson wrote:

> It's possible to have gpio chips hanging off unreliable remote buses
> where the get() operation will fail to acquire a readout of the current
> gpio state. Propagate these errors to the consumer so that they can
> act on, retry or ignore these failing reads, instead of treating them as
> the line being held high.
> 
> Signed-off-by: Bjorn Andersson <bjorn.andersson@...ymobile.com>
> ---
>  drivers/gpio/gpiolib.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 3b5e516298e0..dc17dbf8c234 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -1173,15 +1173,16 @@ EXPORT_SYMBOL_GPL(gpiod_is_active_low);
>   * that the GPIO was actually requested.
>   */
>  
> -static bool _gpiod_get_raw_value(const struct gpio_desc *desc)
> +static int _gpiod_get_raw_value(const struct gpio_desc *desc)
>  {
>  	struct gpio_chip	*chip;
> -	bool value;
>  	int offset;
> +	int value;
>  
>  	chip = desc->chip;
>  	offset = gpio_chip_hwgpio(desc);
> -	value = chip->get ? chip->get(chip, offset) : false;
> +	value = chip->get ? chip->get(chip, offset) : -EIO;

Linus, Alexandre, please feel free to apply this with -ENOTSUPP in
accordance to Alexandre's comment in [1], if you prefer that. I picked
-EIO as that's what's used in most other places when the get() op is
missing.

Maybe we should follow up with separate patch to make that consistent?

[1] https://lkml.org/lkml/2015/8/31/8

> +	value = value < 0 ? value : !!value;
>  	trace_gpio_value(desc_to_gpio(desc), 1, value);
>  	return value;
>  }

Regards,
Bjorn
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