linux-kernel - Re: [PATCH 3/3] gpio: Add reference counting for non-exclusive GPIOs

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Date:   Fri, 23 Nov 2018 10:25:08 +0100
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Charles Keepax <ckeepax@...nsource.cirrus.com>, broonie@...nel.org
Cc:     linus.walleij@...aro.org, lgirdwood@...il.com,
        linux-kernel@...r.kernel.org, patches@...nsource.cirrus.com
Subject: Re: [PATCH 3/3] gpio: Add reference counting for non-exclusive
 GPIOs

Hi Charles,

On 2018-11-22 18:30, Charles Keepax wrote:
> Currently, a GPIO can be requested multiple times when the
> NONEXCLUSIVE flag is set, however it must still be freed a single
> time. This makes client code rather complex, since multiple drivers
> may request the GPIO but only a single one can free it. Rather than
> manually handling this in each driver add some basic reference
> counting into the core.  Currently, this is fairly primitive but
> so is the support for the NONEXCLUSIVE flag and the implementation
> covers those use-cases.
>
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Signed-off-by: Charles Keepax <ckeepax@...nsource.cirrus.com>
Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>
> ---
>  drivers/gpio/gpiolib.c | 13 ++++++++++++-
>  drivers/gpio/gpiolib.h |  2 ++
>  2 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 230e41562462b..42ba86fb495a5 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -2407,6 +2407,13 @@ static bool gpiod_free_commit(struct gpio_desc *desc)
>  
>  	might_sleep();
>  
> +	if (desc->n_users > 1) {
> +		desc->n_users--;
> +		return true;
> +	} else {
> +		desc->n_users = 0;
> +	}
> +
>  	gpiod_unexport(desc);
>  
>  	spin_lock_irqsave(&gpio_lock, flags);
> @@ -4142,7 +4149,8 @@ struct gpio_desc *__must_check gpiod_get_index(struct device *dev,
>  			 */
>  			dev_info(dev, "nonexclusive access to GPIO for %s\n",
>  				 con_id ? con_id : devname);
> -			return desc;
> +
> +			goto done;
>  		} else {
>  			return ERR_PTR(status);
>  		}
> @@ -4155,6 +4163,9 @@ struct gpio_desc *__must_check gpiod_get_index(struct device *dev,
>  		return ERR_PTR(status);
>  	}
>  
> +done:
> +	desc->n_users++;
> +
>  	return desc;
>  }
>  EXPORT_SYMBOL_GPL(gpiod_get_index);
> diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
> index 087d865286a0c..f96eda90281a3 100644
> --- a/drivers/gpio/gpiolib.h
> +++ b/drivers/gpio/gpiolib.h
> @@ -230,6 +230,8 @@ struct gpio_desc {
>  	const char		*label;
>  	/* Name of the GPIO */
>  	const char		*name;
> +
> +	unsigned int		n_users;
>  };
>  
>  int gpiod_request(struct gpio_desc *desc, const char *label);

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