diff options
Diffstat (limited to 'drivers/spi/spi-gpio.c')
| -rw-r--r-- | drivers/spi/spi-gpio.c | 429 |
1 files changed, 429 insertions, 0 deletions
diff --git a/drivers/spi/spi-gpio.c b/drivers/spi/spi-gpio.c new file mode 100644 index 00000000000..0e88ab74549 --- /dev/null +++ b/drivers/spi/spi-gpio.c @@ -0,0 +1,429 @@ +/* + * SPI master driver using generic bitbanged GPIO + * + * Copyright (C) 2006,2008 David Brownell + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. + */ +#include <linux/kernel.h> +#include <linux/init.h> +#include <linux/platform_device.h> +#include <linux/gpio.h> + +#include <linux/spi/spi.h> +#include <linux/spi/spi_bitbang.h> +#include <linux/spi/spi_gpio.h> + + +/* + * This bitbanging SPI master driver should help make systems usable + * when a native hardware SPI engine is not available, perhaps because + * its driver isn't yet working or because the I/O pins it requires + * are used for other purposes. + * + * platform_device->driver_data ... points to spi_gpio + * + * spi->controller_state ... reserved for bitbang framework code + * spi->controller_data ... holds chipselect GPIO + * + * spi->master->dev.driver_data ... points to spi_gpio->bitbang + */ + +struct spi_gpio { + struct spi_bitbang bitbang; + struct spi_gpio_platform_data pdata; + struct platform_device *pdev; +}; + +/*----------------------------------------------------------------------*/ + +/* + * Because the overhead of going through four GPIO procedure calls + * per transferred bit can make performance a problem, this code + * is set up so that you can use it in either of two ways: + * + * - The slow generic way: set up platform_data to hold the GPIO + * numbers used for MISO/MOSI/SCK, and issue procedure calls for + * each of them. This driver can handle several such busses. + * + * - The quicker inlined way: only helps with platform GPIO code + * that inlines operations for constant GPIOs. This can give + * you tight (fast!) inner loops, but each such bus needs a + * new driver. You'll define a new C file, with Makefile and + * Kconfig support; the C code can be a total of six lines: + * + * #define DRIVER_NAME "myboard_spi2" + * #define SPI_MISO_GPIO 119 + * #define SPI_MOSI_GPIO 120 + * #define SPI_SCK_GPIO 121 + * #define SPI_N_CHIPSEL 4 + * #include "spi-gpio.c" + */ + +#ifndef DRIVER_NAME +#define DRIVER_NAME "spi_gpio" + +#define GENERIC_BITBANG /* vs tight inlines */ + +/* all functions referencing these symbols must define pdata */ +#define SPI_MISO_GPIO ((pdata)->miso) +#define SPI_MOSI_GPIO ((pdata)->mosi) +#define SPI_SCK_GPIO ((pdata)->sck) + +#define SPI_N_CHIPSEL ((pdata)->num_chipselect) + +#endif + +/*----------------------------------------------------------------------*/ + +static inline const struct spi_gpio_platform_data * __pure +spi_to_pdata(const struct spi_device *spi) +{ + const struct spi_bitbang *bang; + const struct spi_gpio *spi_gpio; + + bang = spi_master_get_devdata(spi->master); + spi_gpio = container_of(bang, struct spi_gpio, bitbang); + return &spi_gpio->pdata; +} + +/* this is #defined to avoid unused-variable warnings when inlining */ +#define pdata spi_to_pdata(spi) + +static inline void setsck(const struct spi_device *spi, int is_on) +{ + gpio_set_value(SPI_SCK_GPIO, is_on); +} + +static inline void setmosi(const struct spi_device *spi, int is_on) +{ + gpio_set_value(SPI_MOSI_GPIO, is_on); +} + +static inline int getmiso(const struct spi_device *spi) +{ + return !!gpio_get_value(SPI_MISO_GPIO); +} + +#undef pdata + +/* + * NOTE: this clocks "as fast as we can". It "should" be a function of the + * requested device clock. Software overhead means we usually have trouble + * reaching even one Mbit/sec (except when we can inline bitops), so for now + * we'll just assume we never need additional per-bit slowdowns. + */ +#define spidelay(nsecs) do {} while (0) + +#include "spi-bitbang-txrx.h" + +/* + * These functions can leverage inline expansion of GPIO calls to shrink + * costs for a txrx bit, often by factors of around ten (by instruction + * count). That is particularly visible for larger word sizes, but helps + * even with default 8-bit words. + * + * REVISIT overheads calling these functions for each word also have + * significant performance costs. Having txrx_bufs() calls that inline + * the txrx_word() logic would help performance, e.g. on larger blocks + * used with flash storage or MMC/SD. There should also be ways to make + * GCC be less stupid about reloading registers inside the I/O loops, + * even without inlined GPIO calls; __attribute__((hot)) on GCC 4.3? + */ + +static u32 spi_gpio_txrx_word_mode0(struct spi_device *spi, + unsigned nsecs, u32 word, u8 bits) +{ + return bitbang_txrx_be_cpha0(spi, nsecs, 0, 0, word, bits); +} + +static u32 spi_gpio_txrx_word_mode1(struct spi_device *spi, + unsigned nsecs, u32 word, u8 bits) +{ + return bitbang_txrx_be_cpha1(spi, nsecs, 0, 0, word, bits); +} + +static u32 spi_gpio_txrx_word_mode2(struct spi_device *spi, + unsigned nsecs, u32 word, u8 bits) +{ + return bitbang_txrx_be_cpha0(spi, nsecs, 1, 0, word, bits); +} + +static u32 spi_gpio_txrx_word_mode3(struct spi_device *spi, + unsigned nsecs, u32 word, u8 bits) +{ + return bitbang_txrx_be_cpha1(spi, nsecs, 1, 0, word, bits); +} + +/* + * These functions do not call setmosi or getmiso if respective flag + * (SPI_MASTER_NO_RX or SPI_MASTER_NO_TX) is set, so they are safe to + * call when such pin is not present or defined in the controller. + * A separate set of callbacks is defined to get highest possible + * speed in the generic case (when both MISO and MOSI lines are + * available), as optimiser will remove the checks when argument is + * constant. + */ + +static u32 spi_gpio_spec_txrx_word_mode0(struct spi_device *spi, + unsigned nsecs, u32 word, u8 bits) +{ + unsigned flags = spi->master->flags; + return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits); +} + +static u32 spi_gpio_spec_txrx_word_mode1(struct spi_device *spi, + unsigned nsecs, u32 word, u8 bits) +{ + unsigned flags = spi->master->flags; + return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits); +} + +static u32 spi_gpio_spec_txrx_word_mode2(struct spi_device *spi, + unsigned nsecs, u32 word, u8 bits) +{ + unsigned flags = spi->master->flags; + return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits); +} + +static u32 spi_gpio_spec_txrx_word_mode3(struct spi_device *spi, + unsigned nsecs, u32 word, u8 bits) +{ + unsigned flags = spi->master->flags; + return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits); +} + +/*----------------------------------------------------------------------*/ + +static void spi_gpio_chipselect(struct spi_device *spi, int is_active) +{ + unsigned long cs = (unsigned long) spi->controller_data; + + /* set initial clock polarity */ + 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) +{ + unsigned long cs = (unsigned long) spi->controller_data; + int status = 0; + + if (spi->bits_per_word > 32) + 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 && cs != SPI_GPIO_NO_CHIPSELECT) + gpio_free(cs); + } + return status; +} + +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); +} + +static int __init spi_gpio_alloc(unsigned pin, const char *label, bool is_in) +{ + int value; + + value = gpio_request(pin, label); + if (value == 0) { + if (is_in) + value = gpio_direction_input(pin); + else + value = gpio_direction_output(pin, 0); + } + return value; +} + +static int __init +spi_gpio_request(struct spi_gpio_platform_data *pdata, const char *label, + u16 *res_flags) +{ + int value; + + /* NOTE: SPI_*_GPIO symbols may reference "pdata" */ + + if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI) { + value = spi_gpio_alloc(SPI_MOSI_GPIO, label, false); + if (value) + goto done; + } else { + /* HW configuration without MOSI pin */ + *res_flags |= SPI_MASTER_NO_TX; + } + + if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO) { + value = spi_gpio_alloc(SPI_MISO_GPIO, label, true); + if (value) + goto free_mosi; + } else { + /* HW configuration without MISO pin */ + *res_flags |= SPI_MASTER_NO_RX; + } + + value = spi_gpio_alloc(SPI_SCK_GPIO, label, false); + if (value) + goto free_miso; + + goto done; + +free_miso: + if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO) + gpio_free(SPI_MISO_GPIO); +free_mosi: + if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI) + gpio_free(SPI_MOSI_GPIO); +done: + return value; +} + +static int __init spi_gpio_probe(struct platform_device *pdev) +{ + int status; + struct spi_master *master; + struct spi_gpio *spi_gpio; + struct spi_gpio_platform_data *pdata; + u16 master_flags = 0; + + pdata = pdev->dev.platform_data; +#ifdef GENERIC_BITBANG + if (!pdata || !pdata->num_chipselect) + return -ENODEV; +#endif + + status = spi_gpio_request(pdata, dev_name(&pdev->dev), &master_flags); + if (status < 0) + return status; + + master = spi_alloc_master(&pdev->dev, sizeof *spi_gpio); + if (!master) { + status = -ENOMEM; + goto gpio_free; + } + spi_gpio = spi_master_get_devdata(master); + platform_set_drvdata(pdev, spi_gpio); + + spi_gpio->pdev = pdev; + if (pdata) + spi_gpio->pdata = *pdata; + + master->flags = master_flags; + master->bus_num = pdev->id; + master->num_chipselect = SPI_N_CHIPSEL; + master->setup = spi_gpio_setup; + master->cleanup = spi_gpio_cleanup; + + spi_gpio->bitbang.master = spi_master_get(master); + spi_gpio->bitbang.chipselect = spi_gpio_chipselect; + + if ((master_flags & (SPI_MASTER_NO_TX | SPI_MASTER_NO_RX)) == 0) { + spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0; + spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1; + spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2; + spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3; + } else { + spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0; + spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1; + spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2; + spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3; + } + spi_gpio->bitbang.setup_transfer = spi_bitbang_setup_transfer; + spi_gpio->bitbang.flags = SPI_CS_HIGH; + + status = spi_bitbang_start(&spi_gpio->bitbang); + if (status < 0) { + spi_master_put(spi_gpio->bitbang.master); +gpio_free: + if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO) + gpio_free(SPI_MISO_GPIO); + if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI) + gpio_free(SPI_MOSI_GPIO); + gpio_free(SPI_SCK_GPIO); + spi_master_put(master); + } + + return status; +} + +static int __exit spi_gpio_remove(struct platform_device *pdev) +{ + struct spi_gpio *spi_gpio; + struct spi_gpio_platform_data *pdata; + int status; + + spi_gpio = platform_get_drvdata(pdev); + pdata = pdev->dev.platform_data; + + /* stop() unregisters child devices too */ + status = spi_bitbang_stop(&spi_gpio->bitbang); + spi_master_put(spi_gpio->bitbang.master); + + platform_set_drvdata(pdev, NULL); + + if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO) + gpio_free(SPI_MISO_GPIO); + if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI) + gpio_free(SPI_MOSI_GPIO); + gpio_free(SPI_SCK_GPIO); + + return status; +} + +MODULE_ALIAS("platform:" DRIVER_NAME); + +static struct platform_driver spi_gpio_driver = { + .driver.name = DRIVER_NAME, + .driver.owner = THIS_MODULE, + .remove = __exit_p(spi_gpio_remove), +}; + +static int __init spi_gpio_init(void) +{ + return platform_driver_probe(&spi_gpio_driver, spi_gpio_probe); +} +module_init(spi_gpio_init); + +static void __exit spi_gpio_exit(void) +{ + platform_driver_unregister(&spi_gpio_driver); +} +module_exit(spi_gpio_exit); + + +MODULE_DESCRIPTION("SPI master driver using generic bitbanged GPIO "); +MODULE_AUTHOR("David Brownell"); +MODULE_LICENSE("GPL"); |