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3c8e1a84fd
There are some boards that do not strictly follow SPI standard and use only 3 wires (SCLK, MOSI or MISO, SS) for connecting some simple auxiliary chips and controls them with GPIO based 'spi controller'. In this configuration the MISO or MOSI line is missing (it is not required if the chip does not transfer any data back to host or host only reads data from chip). This patch adds support for such non-standard configuration in GPIO-based SPI controller. It has been tested in configuration without MISO pin. Reviewed-by: Kyungmin Park <kyungmin.park@samsung.com> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> Acked-by: David Brownell <dbrownell@users.sourceforge.net> Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
72 lines
2.5 KiB
C
72 lines
2.5 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 MISO or MOSI pin is not available then it should be set to
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* SPI_GPIO_NO_MISO or SPI_GPIO_NO_MOSI.
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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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#define SPI_GPIO_NO_MISO ((unsigned long)-1l)
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#define SPI_GPIO_NO_MOSI ((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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