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

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Date:   Fri, 12 Oct 2018 11:30:34 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>
CC:     <linux-kernel@...r.kernel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH] gpio/regulator: Allow nonexclusive GPIO access

Hi Linus,

On 11/10/18 15:35, 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>

This also fixes a regression I was seeing on Tegra124 Jetson TK1. So ...

Tested-by: Jon Hunter <jonathanh@...dia.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);

Nit-pick, for me the 'con_id' is NULL so should we use the same ternary
operator here as above to print devname instead in this case?

Cheers!
Jon

-- 
nvpublic