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

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Date:   Thu, 11 Oct 2018 15:43:30 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Liam Girdwood <lgirdwood@...il.com>, linux-kernel@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH] gpio/regulator: Allow nonexclusive GPIO access

On Thu, Oct 11, 2018 at 04:35:31PM +0200, Linus Walleij wrote:

> +	/*
> +	 * 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;
> +

It's not just fixed regulators that do this, often regulators with
register control can do this as well.  Since power up is often a
performance critical path but regulators tend to be controlled via slow
buses like I2C it's common to have register control combined with a GPIO
enable line so you don't need to use the bus to do the enables.  That
should just be a case of adding this flag to all the drivers that have
already been converted to gpiod (including the core code that's in
regulator_ena_gpio_request() which I thought was coping with this
already) unless I'm missing something?

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