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| author | Michael Buesch <mb@bu3sch.de> | 2009-04-02 16:57:07 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-04-02 19:04:51 -0700 |
| commit | bfb9bcdbda9a61bca469bf899a589918c60c4c18 (patch) | |
| tree | 40b28178c9d969c94e2039b27ac213cab5de0e79 | |
| parent | 8a0cecffeb52363a57257bbbbd58f4c4537a75bb (diff) | |
| download | kernel_samsung_tuna-bfb9bcdbda9a61bca469bf899a589918c60c4c18.zip kernel_samsung_tuna-bfb9bcdbda9a61bca469bf899a589918c60c4c18.tar.gz kernel_samsung_tuna-bfb9bcdbda9a61bca469bf899a589918c60c4c18.tar.bz2 | |
spi-gpio: allow operation without CS signal
Change spi-gpio so that it is possible to drive SPI communications over
GPIO without the need for a chipselect signal.
This is useful in very small setups where there's only one slave device
on the bus.
This patch does not affect existing setups.
I use this for a tiny communication channel between an embedded device and
a microcontroller. There are not enough GPIOs available for chipselect
and it's not needed anyway in this case.
Signed-off-by: Michael Buesch <mb@bu3sch.de>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | drivers/spi/spi_gpio.c | 21 | ||||
| -rw-r--r-- | include/linux/spi/spi_gpio.h | 6 |
2 files changed, 19 insertions, 8 deletions
diff --git a/drivers/spi/spi_gpio.c b/drivers/spi/spi_gpio.c index d2866c2..26bd03e 100644 --- a/drivers/spi/spi_gpio.c +++ b/drivers/spi/spi_gpio.c @@ -178,8 +178,10 @@ static void spi_gpio_chipselect(struct spi_device *spi, int is_active) if (is_active) setsck(spi, spi->mode & SPI_CPOL); - /* SPI is normally active-low */ - gpio_set_value(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active); + if (cs != SPI_GPIO_NO_CHIPSELECT) { + /* SPI is normally active-low */ + gpio_set_value(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active); + } } static int spi_gpio_setup(struct spi_device *spi) @@ -191,15 +193,17 @@ static int spi_gpio_setup(struct spi_device *spi) return -EINVAL; if (!spi->controller_state) { - status = gpio_request(cs, dev_name(&spi->dev)); - if (status) - return status; - status = gpio_direction_output(cs, spi->mode & SPI_CS_HIGH); + if (cs != SPI_GPIO_NO_CHIPSELECT) { + status = gpio_request(cs, dev_name(&spi->dev)); + if (status) + return status; + status = gpio_direction_output(cs, spi->mode & SPI_CS_HIGH); + } } if (!status) status = spi_bitbang_setup(spi); if (status) { - if (!spi->controller_state) + if (!spi->controller_state && cs != SPI_GPIO_NO_CHIPSELECT) gpio_free(cs); } return status; @@ -209,7 +213,8 @@ static void spi_gpio_cleanup(struct spi_device *spi) { unsigned long cs = (unsigned long) spi->controller_data; - gpio_free(cs); + if (cs != SPI_GPIO_NO_CHIPSELECT) + gpio_free(cs); spi_bitbang_cleanup(spi); } diff --git a/include/linux/spi/spi_gpio.h b/include/linux/spi/spi_gpio.h index 0f01a0f..ca6782e 100644 --- a/include/linux/spi/spi_gpio.h +++ b/include/linux/spi/spi_gpio.h @@ -25,10 +25,16 @@ * ... * }; * + * If chipselect is not used (there's only one device on the bus), assign + * SPI_GPIO_NO_CHIPSELECT to the controller_data: + * .controller_data = (void *) SPI_GPIO_NO_CHIPSELECT; + * * If the bitbanged bus is later switched to a "native" controller, * that platform_device and controller_data should be removed. */ +#define SPI_GPIO_NO_CHIPSELECT ((unsigned long)-1l) + /** * struct spi_gpio_platform_data - parameter for bitbanged SPI master * @sck: number of the GPIO used for clock output |