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bfb9bcdbda
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>
67 lines
2.3 KiB
C
67 lines
2.3 KiB
C
#ifndef __LINUX_SPI_GPIO_H
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#define __LINUX_SPI_GPIO_H
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/*
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* For each bitbanged SPI bus, set up a platform_device node with:
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* - name "spi_gpio"
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* - id the same as the SPI bus number it implements
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* - dev.platform data pointing to a struct spi_gpio_platform_data
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*
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* Or, see the driver code for information about speedups that are
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* possible on platforms that support inlined access for GPIOs (no
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* spi_gpio_platform_data is used).
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*
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* Use spi_board_info with these busses in the usual way, being sure
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* that the controller_data being the GPIO used for each device's
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* chipselect:
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*
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* static struct spi_board_info ... [] = {
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* ...
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* // this slave uses GPIO 42 for its chipselect
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* .controller_data = (void *) 42,
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* ...
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* // this one uses GPIO 86 for its chipselect
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* .controller_data = (void *) 86,
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* ...
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* };
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*
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* If chipselect is not used (there's only one device on the bus), assign
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* SPI_GPIO_NO_CHIPSELECT to the controller_data:
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* .controller_data = (void *) SPI_GPIO_NO_CHIPSELECT;
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*
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* If the bitbanged bus is later switched to a "native" controller,
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* that platform_device and controller_data should be removed.
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*/
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#define SPI_GPIO_NO_CHIPSELECT ((unsigned long)-1l)
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/**
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* struct spi_gpio_platform_data - parameter for bitbanged SPI master
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* @sck: number of the GPIO used for clock output
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* @mosi: number of the GPIO used for Master Output, Slave In (MOSI) data
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* @miso: number of the GPIO used for Master Input, Slave Output (MISO) data
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* @num_chipselect: how many slaves to allow
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*
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* All GPIO signals used with the SPI bus managed through this driver
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* (chipselects, MOSI, MISO, SCK) must be configured as GPIOs, instead
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* of some alternate function.
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*
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* It can be convenient to use this driver with pins that have alternate
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* functions associated with a "native" SPI controller if a driver for that
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* controller is not available, or is missing important functionality.
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*
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* On platforms which can do so, configure MISO with a weak pullup unless
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* there's an external pullup on that signal. That saves power by avoiding
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* floating signals. (A weak pulldown would save power too, but many
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* drivers expect to see all-ones data as the no slave "response".)
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*/
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struct spi_gpio_platform_data {
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unsigned sck;
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unsigned mosi;
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unsigned miso;
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u16 num_chipselect;
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};
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#endif /* __LINUX_SPI_GPIO_H */
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