/*
* spi_gpio.c - 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)
#define EXPAND_BITBANG_TXRX
#include <linux/spi/spi_bitbang.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, 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, 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, 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, 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);
/* 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) {
status = gpio_request(cs, spi->dev.bus_id);
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)
gpio_free(cs);
}
return status;
}
static void spi_gpio_cleanup(struct spi_device *spi)
{
unsigned long cs = (unsigned long) spi->controller_data;
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)
{
int value;
/* NOTE: SPI_*_GPIO symbols may reference "pdata" */
value = spi_gpio_alloc(SPI_MOSI_GPIO, label, false);
if (value)
goto done;
value = spi_gpio_alloc(SPI_MISO_GPIO, label, true);
if (value)
goto free_mosi;
value = spi_gpio_alloc(SPI_SCK_GPIO, label, false);
if (value)
goto free_miso;
goto done;
free_miso:
gpio_free(SPI_MISO_GPIO);
free_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;
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));
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->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;
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;
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:
gpio_free(SPI_MISO_GPIO);
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);
gpio_free(SPI_MISO_GPIO);
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");
