Commit 28735a72 authored by David Brownell's avatar David Brownell Committed by Linus Torvalds
Browse files

[PATCH] gpio_direction_output() needs an initial value 



It's been pointed out that output GPIOs should have an initial value, to
avoid signal glitching ...  among other things, it can be some time before
a driver is ready.  This patch corrects that oversight, fixing

 - documentation
 - platforms supporting the GPIO interface
 - users of that call (just one for now, others are pending)

There's only one user of this call for now since most platforms are still
using non-generic GPIO setup code, which in most cases already couples the
initial value with its "set output mode" request.

Note that most platforms are clear about the hardware letting the output
value be set before the pin direction is changed, but the s3c241x docs are
vague on that topic ...  so those chips might not avoid the glitches.

Signed-off-by: default avatarDavid Brownell <dbrownell@users.sourceforge.net>
Acked-by: default avatarAndrew Victor <andrew@sanpeople.com>
Acked-by: default avatarMilan Svoboda <msvoboda@ra.rockwell.com>
Acked-by: default avatarHaavard Skinnemoen <hskinnemoen@atmel.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a836f585

Documentation/gpio.txt

+4 −1
Original line number Diff line number Diff line
@@ -105,12 +105,15 @@ setting up a platform_device using the GPIO, is mark its direction: 


	/* set as input or output, returning 0 or negative errno */

	int gpio_direction_input(unsigned gpio);

	int gpio_direction_output(unsigned gpio);

	int gpio_direction_output(unsigned gpio, int value);



The return value is zero for success, else a negative errno.  It should

be checked, since the get/set calls don't have error returns and since

misconfiguration is possible.  (These calls could sleep.)



For output GPIOs, the value provided becomes the initial output value.

This helps avoid signal glitching during system startup.



Setting the direction can fail if the GPIO number is invalid, or when

that particular GPIO can't be used in that mode.  It's generally a bad

idea to rely on boot firmware to have set the direction correctly, since

arch/arm/mach-at91/gpio.c

+2 −1
Original line number Diff line number Diff line
@@ -215,13 +215,14 @@ int gpio_direction_input(unsigned pin) 
}

EXPORT_SYMBOL(gpio_direction_input);



int gpio_direction_output(unsigned pin)

int gpio_direction_output(unsigned pin, int value)

{

	void __iomem	*pio = pin_to_controller(pin);

	unsigned	mask = pin_to_mask(pin);



	if (!pio || !(__raw_readl(pio + PIO_PSR) & mask))

		return -EINVAL;

	__raw_writel(mask, pio + (value ? PIO_SODR : PIO_CODR));

	__raw_writel(mask, pio + PIO_OER);

	return 0;

}

arch/arm/mach-sa1100/generic.c

+2 −1
Original line number Diff line number Diff line
@@ -153,7 +153,7 @@ int gpio_direction_input(unsigned gpio) 


EXPORT_SYMBOL(gpio_direction_input);



int gpio_direction_output(unsigned gpio)

int gpio_direction_output(unsigned gpio, int value)

{

	unsigned long flags;
@@ -161,6 +161,7 @@ int gpio_direction_output(unsigned gpio) 
		return -EINVAL;



	local_irq_save(flags);

	gpio_set_value(gpio, value);

	GPDR |= GPIO_GPIO(gpio);

	local_irq_restore(flags);

	return 0;

arch/avr32/mach-at32ap/pio.c

+3 −1
Original line number Diff line number Diff line
@@ -214,7 +214,7 @@ int gpio_direction_input(unsigned int gpio) 
}

EXPORT_SYMBOL(gpio_direction_input);



int gpio_direction_output(unsigned int gpio)

int gpio_direction_output(unsigned int gpio, int value)

{

	struct pio_device *pio;

	unsigned int pin;
@@ -223,6 +223,8 @@ int gpio_direction_output(unsigned int gpio) 
	if (!pio)

		return -ENODEV;



	gpio_set_value(gpio, value);



	pin = gpio & 0x1f;

	pio_writel(pio, OER, 1 << pin);

drivers/spi/atmel_spi.c

+1 −1
Original line number Diff line number Diff line
@@ -425,7 +425,7 @@ static int atmel_spi_setup(struct spi_device *spi) 
		if (ret)

			return ret;

		spi->controller_state = (void *)npcs_pin;

		gpio_direction_output(npcs_pin);

		gpio_direction_output(npcs_pin, !(spi->mode & SPI_CS_HIGH));

	}



	dev_dbg(&spi->dev,

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