Commit d29389de authored by David Brownell's avatar David Brownell Committed by Linus Torvalds

spi_gpio driver

Generalize the old at91rm9200 "bootstrap" bitbanging SPI master driver as
"spi_gpio", so it works with arbitrary GPIOs and can be configured through
platform_data.  Such SPI masters support:

 - any number of bus instances (bus_num is the platform_device.id)
 - any number of chipselects (one GPIO per spi_device)
 - all four SPI_MODE values, and SPI_CS_HIGH
 - i/o word sizes from 1 to 32 bits;
 - devices configured as with any other spi_master controller

When configured using platform_data, this provides relatively low clock
rates.  On platforms that support inlined GPIO calls, significantly
improved transfer speeds are also possible with a semi-custom driver.
(It's still painful when accessing flash memory, but less so.)

Sanity checked by using this version to replace both native controllers on
a board with six different SPI slaves, relying on three different
SPI_MODE_* values and both SPI_CS_HIGH settings for correct operation.

[akpm@linux-foundation.org: cleanups]
Signed-off-by: default avatarDavid Brownell <dbrownell@users.sourceforge.net>
Acked-by: default avatarMagnus Damm <damm@igel.co.jp>
Tested-by: default avatarMagnus Damm <damm@igel.co.jp>
Cc: Torgil Svensson <torgil.svensson@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c2bacfc4
...@@ -78,7 +78,7 @@ config SPI_AU1550 ...@@ -78,7 +78,7 @@ config SPI_AU1550
will be called au1550_spi. will be called au1550_spi.
config SPI_BITBANG config SPI_BITBANG
tristate "Bitbanging SPI master" tristate "Utilities for Bitbanging SPI masters"
help help
With a few GPIO pins, your system can bitbang the SPI protocol. With a few GPIO pins, your system can bitbang the SPI protocol.
Select this to get SPI support through I/O pins (GPIO, parallel Select this to get SPI support through I/O pins (GPIO, parallel
...@@ -100,6 +100,22 @@ config SPI_BUTTERFLY ...@@ -100,6 +100,22 @@ config SPI_BUTTERFLY
inexpensive battery powered microcontroller evaluation board. inexpensive battery powered microcontroller evaluation board.
This same cable can be used to flash new firmware. This same cable can be used to flash new firmware.
config SPI_GPIO
tristate "GPIO-based bitbanging SPI Master"
depends on GENERIC_GPIO
select SPI_BITBANG
help
This simple GPIO bitbanging SPI master uses the arch-neutral GPIO
interface to manage MOSI, MISO, SCK, and chipselect signals. SPI
slaves connected to a bus using this driver are configured as usual,
except that the spi_board_info.controller_data holds the GPIO number
for the chipselect used by this controller driver.
Note that this driver often won't achieve even 1 Mbit/sec speeds,
making it unusually slow for SPI. If your platform can inline
GPIO operations, you should be able to leverage that for better
speed with a custom version of this driver; see the source code.
config SPI_IMX config SPI_IMX
tristate "Freescale iMX SPI controller" tristate "Freescale iMX SPI controller"
depends on ARCH_IMX && EXPERIMENTAL depends on ARCH_IMX && EXPERIMENTAL
......
...@@ -16,6 +16,7 @@ obj-$(CONFIG_SPI_BFIN) += spi_bfin5xx.o ...@@ -16,6 +16,7 @@ obj-$(CONFIG_SPI_BFIN) += spi_bfin5xx.o
obj-$(CONFIG_SPI_BITBANG) += spi_bitbang.o obj-$(CONFIG_SPI_BITBANG) += spi_bitbang.o
obj-$(CONFIG_SPI_AU1550) += au1550_spi.o obj-$(CONFIG_SPI_AU1550) += au1550_spi.o
obj-$(CONFIG_SPI_BUTTERFLY) += spi_butterfly.o obj-$(CONFIG_SPI_BUTTERFLY) += spi_butterfly.o
obj-$(CONFIG_SPI_GPIO) += spi_gpio.o
obj-$(CONFIG_SPI_IMX) += spi_imx.o obj-$(CONFIG_SPI_IMX) += spi_imx.o
obj-$(CONFIG_SPI_LM70_LLP) += spi_lm70llp.o obj-$(CONFIG_SPI_LM70_LLP) += spi_lm70llp.o
obj-$(CONFIG_SPI_PXA2XX) += pxa2xx_spi.o obj-$(CONFIG_SPI_PXA2XX) += pxa2xx_spi.o
......
This diff is collapsed.
#ifndef __LINUX_SPI_GPIO_H
#define __LINUX_SPI_GPIO_H
/*
* For each bitbanged SPI bus, set up a platform_device node with:
* - name "spi_gpio"
* - id the same as the SPI bus number it implements
* - dev.platform data pointing to a struct spi_gpio_platform_data
*
* Or, see the driver code for information about speedups that are
* possible on platforms that support inlined access for GPIOs (no
* spi_gpio_platform_data is used).
*
* Use spi_board_info with these busses in the usual way, being sure
* that the controller_data being the GPIO used for each device's
* chipselect:
*
* static struct spi_board_info ... [] = {
* ...
* // this slave uses GPIO 42 for its chipselect
* .controller_data = (void *) 42,
* ...
* // this one uses GPIO 86 for its chipselect
* .controller_data = (void *) 86,
* ...
* };
*
* If the bitbanged bus is later switched to a "native" controller,
* that platform_device and controller_data should be removed.
*/
/**
* struct spi_gpio_platform_data - parameter for bitbanged SPI master
* @sck: number of the GPIO used for clock output
* @mosi: number of the GPIO used for Master Output, Slave In (MOSI) data
* @miso: number of the GPIO used for Master Input, Slave Output (MISO) data
* @num_chipselect: how many slaves to allow
*
* All GPIO signals used with the SPI bus managed through this driver
* (chipselects, MOSI, MISO, SCK) must be configured as GPIOs, instead
* of some alternate function.
*
* It can be convenient to use this driver with pins that have alternate
* functions associated with a "native" SPI controller if a driver for that
* controller is not available, or is missing important functionality.
*
* On platforms which can do so, configure MISO with a weak pullup unless
* there's an external pullup on that signal. That saves power by avoiding
* floating signals. (A weak pulldown would save power too, but many
* drivers expect to see all-ones data as the no slave "response".)
*/
struct spi_gpio_platform_data {
unsigned sck;
unsigned mosi;
unsigned miso;
u16 num_chipselect;
};
#endif /* __LINUX_SPI_GPIO_H */
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