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Date: Sat, 21 Feb 2009 22:01:52 +0100
From: Michael Buesch <mb@...sch.de>
To: David Brownell <dbrownell@...rs.sourceforge.net>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org
Subject: [PATCH] spi-gpio: Allow operation without CS signal
This patch changes 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.
Signed-off-by: Michael Buesch <mb@...sch.de>
---
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.
PS: Dave, please give me some hint on how to fixup the spi-delay patch
that I sent recently. Should I add a member to the spi-gpio pdata that
tells whether to use the delay? This way existing setups would continue
to work unchanged and the max_bus_speed=0 issue would be resolved.
Index: linux-2.6/drivers/spi/spi_gpio.c
===================================================================
--- linux-2.6.orig/drivers/spi/spi_gpio.c 2009-02-21 21:57:03.000000000 +0100
+++ linux-2.6/drivers/spi/spi_gpio.c 2009-02-21 21:57:58.000000000 +0100
@@ -178,8 +178,10 @@ static void spi_gpio_chipselect(struct s
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_dev
return -EINVAL;
if (!spi->controller_state) {
- status = gpio_request(cs, spi->dev.bus_id);
- if (status)
- return status;
- status = gpio_direction_output(cs, spi->mode & SPI_CS_HIGH);
+ if (cs != SPI_GPIO_NO_CHIPSELECT) {
+ status = gpio_request(cs, spi->dev.bus_id);
+ 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_
{
unsigned long cs = (unsigned long) spi->controller_data;
- gpio_free(cs);
+ if (cs != SPI_GPIO_NO_CHIPSELECT)
+ gpio_free(cs);
spi_bitbang_cleanup(spi);
}
Index: linux-2.6/include/linux/spi/spi_gpio.h
===================================================================
--- linux-2.6.orig/include/linux/spi/spi_gpio.h 2009-02-21 21:48:36.000000000 +0100
+++ linux-2.6/include/linux/spi/spi_gpio.h 2009-02-21 21:57:58.000000000 +0100
@@ -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
--
Greetings, Michael.
--
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