Commit bfb9bcdb authored by Michael Buesch's avatar Michael Buesch Committed by Linus Torvalds
Browse files

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: default avatarMichael Buesch <mb@bu3sch.de>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8a0cecff

drivers/spi/spi_gpio.c

+13 −8
Original line number Diff line number Diff line
@@ -178,9 +178,11 @@ static void spi_gpio_chipselect(struct spi_device *spi, int is_active) 
	if (is_active)

		setsck(spi, spi->mode & SPI_CPOL);



	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) {

		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;
@@ -209,6 +213,7 @@ static void spi_gpio_cleanup(struct spi_device *spi) 
{

	unsigned long	cs = (unsigned long) spi->controller_data;



	if (cs != SPI_GPIO_NO_CHIPSELECT)

		gpio_free(cs);

	spi_bitbang_cleanup(spi);

}

include/linux/spi/spi_gpio.h

+6 −0
Original line number Diff line number Diff line
@@ -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

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