linux-kernel - Re: [PATCH] gpio/regulator: Allow nonexclusive GPIO access

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Date:   Thu, 11 Oct 2018 17:15:10 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gpio/regulator: Allow nonexclusive GPIO access

Hi Linus,

On 2018-10-11 16:35, Linus Walleij wrote:
> This allows nonexclusive (simultaneous) access to a single
> GPIO line for the fixed regulator enable line. This happens
> when several regulators use the same GPIO for enabling and
> disabling a regulator, and all need a handle on their GPIO
> descriptor.
>
> This solution with a special flag is not entirely elegant
> and should ideally be replaced by something more careful as
> this makes it possible for several consumers to
> enable/disable the same GPIO line to the left and right
> without any consistency. The current use inside the regulator
> core should however be fine as it takes special care to
> handle this.
>
> For the state of the GPIO backend, this is still the
> lesser evil compared to going back to global GPIO
> numbers.
>
> Fixes: efdfeb079cc3 ("regulator: fixed: Convert to use GPIO descriptor only")
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
> ---

It looks to be fixing the Sii9234 probe issue, but I didn't do any
further tests. I must go out the office and I will be back on Monday.
I think You can add my:

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

> Hi Marek, it would be great if you could try this on top
> of linux-next and report if it solves your problem on the
> Samsung Exynos.
>
> If it does I hope it will apply cleanly on the regulator
> tree.
> ---
>  drivers/gpio/gpiolib.c        | 19 +++++++++++++++++--
>  drivers/regulator/fixed.c     | 13 +++++++++++++
>  include/linux/gpio/consumer.h |  1 +
>  3 files changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 7c222df8f834..f82a741ff428 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -4144,8 +4144,23 @@ struct gpio_desc *__must_check gpiod_get_index(struct device *dev,
>  	 * the device name as label
>  	 */
>  	status = gpiod_request(desc, con_id ? con_id : devname);
> -	if (status < 0)
> -		return ERR_PTR(status);
> +	if (status < 0) {
> +		if (status == -EBUSY && flags & GPIOD_FLAGS_BIT_NONEXCLUSIVE) {
> +			/*
> +			 * This happens when there are several consumers for
> +			 * the same GPIO line: we just return here without
> +			 * further initialization. It is a bit if a hack.
> +			 * This is necessary to support fixed regulators.
> +			 *
> +			 * FIXME: Make this more sane and safe.
> +			 */
> +			dev_info(dev, "nonexclusive access to GPIO for %s\n",
> +				 con_id);
> +			return desc;
> +		} else {
> +			return ERR_PTR(status);
> +		}
> +	}
>  
>  	status = gpiod_configure_flags(desc, con_id, lookupflags, flags);
>  	if (status < 0) {
> diff --git a/drivers/regulator/fixed.c b/drivers/regulator/fixed.c
> index 7d639ad953b6..ccc29038f19a 100644
> --- a/drivers/regulator/fixed.c
> +++ b/drivers/regulator/fixed.c
> @@ -170,6 +170,19 @@ static int reg_fixed_voltage_probe(struct platform_device *pdev)
>  			gflags = GPIOD_OUT_LOW_OPEN_DRAIN;
>  	}
>  
> +	/*
> +	 * Some fixed regulators share the enable line between two
> +	 * regulators which makes it necessary to get a handle on the
> +	 * same descriptor for two different consumers. This will get
> +	 * the GPIO descriptor, but only the first call will initialize
> +	 * it so any flags such as inversion or open drain will only
> +	 * be set up by the first caller and assumed identical on the
> +	 * next caller.
> +	 *
> +	 * FIXME: find a better way to deal with this.
> +	 */
> +	gflags |= GPIOD_FLAGS_BIT_NONEXCLUSIVE;
> +
>  	cfg.ena_gpiod = devm_gpiod_get_optional(&pdev->dev, NULL, gflags);
>  	if (IS_ERR(cfg.ena_gpiod))
>  		return PTR_ERR(cfg.ena_gpiod);
> diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
> index 0f350616d372..f2f887795d43 100644
> --- a/include/linux/gpio/consumer.h
> +++ b/include/linux/gpio/consumer.h
> @@ -39,6 +39,7 @@ struct gpio_descs {
>  #define GPIOD_FLAGS_BIT_DIR_OUT		BIT(1)
>  #define GPIOD_FLAGS_BIT_DIR_VAL		BIT(2)
>  #define GPIOD_FLAGS_BIT_OPEN_DRAIN	BIT(3)
> +#define GPIOD_FLAGS_BIT_NONEXCLUSIVE	BIT(4)
>  
>  /**
>   * Optional flags that can be passed to one of gpiod_* to configure direction

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