From: David Brownell Date: Fri, 16 Mar 2007 21:38:14 +0000 (-0800) Subject: [PATCH] gpio_direction_output() needs an initial value X-Git-Tag: v2.6.21-rc5~99 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=28735a7253a6c24364765e80a5428b4a151fccc2;p=linux-2.6 [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: David Brownell Acked-by: Andrew Victor Acked-by: Milan Svoboda Acked-by: Haavard Skinnemoen Cc: Russell King Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt index 576ce463cf..989f1130f4 100644 --- a/Documentation/gpio.txt +++ b/Documentation/gpio.txt @@ -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 diff --git a/arch/arm/mach-at91/gpio.c b/arch/arm/mach-at91/gpio.c index 44211a0af1..ba4a1bb3ee 100644 --- a/arch/arm/mach-at91/gpio.c +++ b/arch/arm/mach-at91/gpio.c @@ -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; } diff --git a/arch/arm/mach-sa1100/generic.c b/arch/arm/mach-sa1100/generic.c index 192a5a26cf..edc349e5fc 100644 --- a/arch/arm/mach-sa1100/generic.c +++ b/arch/arm/mach-sa1100/generic.c @@ -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; diff --git a/arch/avr32/mach-at32ap/pio.c b/arch/avr32/mach-at32ap/pio.c index 9ba5654cde..1eb99b814f 100644 --- a/arch/avr32/mach-at32ap/pio.c +++ b/arch/avr32/mach-at32ap/pio.c @@ -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); diff --git a/drivers/spi/atmel_spi.c b/drivers/spi/atmel_spi.c index 6fa260d1a9..66e7bc9857 100644 --- a/drivers/spi/atmel_spi.c +++ b/drivers/spi/atmel_spi.c @@ -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, diff --git a/include/asm-arm/arch-at91/gpio.h b/include/asm-arm/arch-at91/gpio.h index 98ad2114f4..0a241e2fb6 100644 --- a/include/asm-arm/arch-at91/gpio.h +++ b/include/asm-arm/arch-at91/gpio.h @@ -223,7 +223,7 @@ static inline void gpio_free(unsigned gpio) } extern int gpio_direction_input(unsigned gpio); -extern int gpio_direction_output(unsigned gpio); +extern int gpio_direction_output(unsigned gpio, int value); static inline int gpio_get_value(unsigned gpio) { diff --git a/include/asm-arm/arch-omap/gpio.h b/include/asm-arm/arch-omap/gpio.h index 3762a6ae6a..590917efc9 100644 --- a/include/asm-arm/arch-omap/gpio.h +++ b/include/asm-arm/arch-omap/gpio.h @@ -113,8 +113,9 @@ static inline int gpio_direction_input(unsigned gpio) return __gpio_set_direction(gpio, 1); } -static inline int gpio_direction_output(unsigned gpio) +static inline int gpio_direction_output(unsigned gpio, int value) { + omap_set_gpio_dataout(gpio, value); return __gpio_set_direction(gpio, 0); } diff --git a/include/asm-arm/arch-pxa/gpio.h b/include/asm-arm/arch-pxa/gpio.h index 3d348a3511..aeba24347f 100644 --- a/include/asm-arm/arch-pxa/gpio.h +++ b/include/asm-arm/arch-pxa/gpio.h @@ -43,9 +43,9 @@ static inline int gpio_direction_input(unsigned gpio) return pxa_gpio_mode(gpio | GPIO_IN); } -static inline int gpio_direction_output(unsigned gpio) +static inline int gpio_direction_output(unsigned gpio, int value) { - return pxa_gpio_mode(gpio | GPIO_OUT); + return pxa_gpio_mode(gpio | GPIO_OUT | (value ? 0 : GPIO_DFLT_LOW)); } static inline int __gpio_get_value(unsigned gpio) diff --git a/include/asm-arm/arch-s3c2410/gpio.h b/include/asm-arm/arch-s3c2410/gpio.h index d47ae453f8..7583895fd3 100644 --- a/include/asm-arm/arch-s3c2410/gpio.h +++ b/include/asm-arm/arch-s3c2410/gpio.h @@ -44,9 +44,11 @@ static inline int gpio_direction_input(unsigned gpio) return 0; } -static inline int gpio_direction_output(unsigned gpio) +static inline int gpio_direction_output(unsigned gpio, int value) { s3c2410_gpio_cfgpin(gpio, S3C2410_GPIO_OUTPUT); + /* REVISIT can we write the value first, to avoid glitching? */ + s3c2410_gpio_setpin(gpio, value); return 0; } diff --git a/include/asm-arm/arch-sa1100/gpio.h b/include/asm-arm/arch-sa1100/gpio.h index da7575b0e5..e7a9d26e22 100644 --- a/include/asm-arm/arch-sa1100/gpio.h +++ b/include/asm-arm/arch-sa1100/gpio.h @@ -38,7 +38,7 @@ static inline void gpio_free(unsigned gpio) } extern int gpio_direction_input(unsigned gpio); -extern int gpio_direction_output(unsigned gpio); +extern int gpio_direction_output(unsigned gpio, int value); static inline int gpio_get_value(unsigned gpio) diff --git a/include/asm-avr32/arch-at32ap/gpio.h b/include/asm-avr32/arch-at32ap/gpio.h index fcb756bdaa..80a21aa9ae 100644 --- a/include/asm-avr32/arch-at32ap/gpio.h +++ b/include/asm-avr32/arch-at32ap/gpio.h @@ -10,7 +10,7 @@ int __must_check gpio_request(unsigned int gpio, const char *label); void gpio_free(unsigned int gpio); int gpio_direction_input(unsigned int gpio); -int gpio_direction_output(unsigned int gpio); +int gpio_direction_output(unsigned int gpio, int value); int gpio_get_value(unsigned int gpio); void gpio_set_value(unsigned int gpio, int value);