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authorMichael Buesch <mb@bu3sch.de>2009-04-03 03:57:07 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2009-04-03 06:04:51 +0400
commitbfb9bcdbda9a61bca469bf899a589918c60c4c18 (patch)
tree40b28178c9d969c94e2039b27ac213cab5de0e79 /drivers/spi
parent8a0cecffeb52363a57257bbbbd58f4c4537a75bb (diff)
downloadlinux-bfb9bcdbda9a61bca469bf899a589918c60c4c18.tar.xz
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>
Diffstat (limited to 'drivers/spi')
-rw-r--r--drivers/spi/spi_gpio.c21
1 files changed, 13 insertions, 8 deletions
diff --git a/drivers/spi/spi_gpio.c b/drivers/spi/spi_gpio.c
index d2866c293dee..26bd03e61855 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);
}