linux-kernel - Re: [PATCH 10/20] gpio: pca953x: Add optional reset gpio control

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Date:   Fri, 30 Dec 2016 08:06:23 +0100
From:   Lothar Waßmann <LW@...O-electronics.de>
To:     Steve Longerbeam <slongerbeam@...il.com>
Cc:     shawnguo@...nel.org, kernel@...gutronix.de, fabio.estevam@....com,
        robh+dt@...nel.org, mark.rutland@....com, linux@...linux.org.uk,
        linus.walleij@...aro.org, gnurou@...il.com, mchehab@...nel.org,
        gregkh@...uxfoundation.org, p.zabel@...gutronix.de,
        devel@...verdev.osuosl.org, devicetree@...r.kernel.org,
        Steve Longerbeam <steve_longerbeam@...tor.com>,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org
Subject: Re: [PATCH 10/20] gpio: pca953x: Add optional reset gpio control

Hi,

On Thu, 29 Dec 2016 14:27:25 -0800 Steve Longerbeam wrote:
> Add optional reset-gpios pin control. If present, de-assert the
> specified reset gpio pin to bring the chip out of reset.
> 
> Signed-off-by: Steve Longerbeam <steve_longerbeam@...tor.com>
> Cc: Linus Walleij <linus.walleij@...aro.org>
> Cc: Alexandre Courbot <gnurou@...il.com>
> Cc: linux-gpio@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> 
> ---
> 
> v2:
> - documented optional reset-gpios property in
>   Documentation/devicetree/bindings/gpio/gpio-pca953x.txt.
> ---
>  Documentation/devicetree/bindings/gpio/gpio-pca953x.txt |  4 ++++
>  drivers/gpio/gpio-pca953x.c                             | 17 +++++++++++++++++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/gpio/gpio-pca953x.txt b/Documentation/devicetree/bindings/gpio/gpio-pca953x.txt
> index 08dd15f..da54f4c 100644
> --- a/Documentation/devicetree/bindings/gpio/gpio-pca953x.txt
> +++ b/Documentation/devicetree/bindings/gpio/gpio-pca953x.txt
> @@ -29,6 +29,10 @@ Required properties:
>  	onsemi,pca9654
>  	exar,xra1202
>  
> +Optional properties:
> + - reset-gpios: GPIO specification for the RESET input
> +
> +
>  Example:
>  
>  
> diff --git a/drivers/gpio/gpio-pca953x.c b/drivers/gpio/gpio-pca953x.c
> index d5d72d8..d1c0bd5 100644
> --- a/drivers/gpio/gpio-pca953x.c
> +++ b/drivers/gpio/gpio-pca953x.c
> @@ -22,6 +22,7 @@
>  #include <linux/of_platform.h>
>  #include <linux/acpi.h>
>  #include <linux/regulator/consumer.h>
> +#include <linux/gpio/consumer.h>
>  
>  #define PCA953X_INPUT		0
>  #define PCA953X_OUTPUT		1
> @@ -133,6 +134,7 @@ struct pca953x_chip {
>  	const char *const *names;
>  	unsigned long driver_data;
>  	struct regulator *regulator;
> +	struct gpio_desc *reset_gpio;
>  
>  	const struct pca953x_reg_config *regs;
>  
> @@ -756,6 +758,21 @@ static int pca953x_probe(struct i2c_client *client,
>  	} else {
>  		chip->gpio_start = -1;
>  		irq_base = 0;
> +
> +		/* see if we need to de-assert a reset pin */
> +		chip->reset_gpio = devm_gpiod_get_optional(&client->dev,
> +							   "reset",
> +							   GPIOD_OUT_LOW);

> +		if (IS_ERR(chip->reset_gpio)) {
> +			dev_err(&client->dev, "request for reset pin failed\n");
> +			return PTR_ERR(chip->reset_gpio);
> +		}
> +
> +		if (chip->reset_gpio) {
> +			/* bring chip out of reset */
> +			dev_info(&client->dev, "releasing reset\n");
> +			gpiod_set_value(chip->reset_gpio, 0);
>
The pin is already initialized to the inactive state thru the
GPIOD_OUT_LOW flag in devm_gpiod_get_optional(), so this call to
gpiod_set_value() is useless.


Lothar Waßmann