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SubjectRe: [PATCH] gpio/regulator: Allow nonexclusive GPIO access
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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@samsung.com>
> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

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

Tested-by: Jon Hunter <jonathanh@nvidia.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

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