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authorMichael Buesch <mb@bu3sch.de>2009-04-02 16:57:07 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-04-02 19:04:51 -0700
commitbfb9bcdbda9a61bca469bf899a589918c60c4c18 (patch)
tree40b28178c9d969c94e2039b27ac213cab5de0e79 /include
parent8a0cecffeb52363a57257bbbbd58f4c4537a75bb (diff)
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 'include')
-rw-r--r--include/linux/spi/spi_gpio.h6
1 files changed, 6 insertions, 0 deletions
diff --git a/include/linux/spi/spi_gpio.h b/include/linux/spi/spi_gpio.h
index 0f01a0f1f40..ca6782ee4b9 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