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|
/*
* 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/module.h>
#include <linux/platform_device.h>
#include <linux/gpio.h>
#include <linux/of.h>
#include <linux/of_device.h>
#include <linux/of_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;
int cs_gpios[0];
};
/*----------------------------------------------------------------------*/
/*
* 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 struct spi_gpio * __pure
spi_to_spi_gpio(const struct spi_device *spi)
{
const struct spi_bitbang *bang;
struct spi_gpio *spi_gpio;
bang = spi_master_get_devdata(spi->master);
spi_gpio = container_of(bang, struct spi_gpio, bitbang);
return spi_gpio;
}
static inline struct spi_gpio_platform_data * __pure
spi_to_pdata(const struct spi_device *spi)
{
return &spi_to_spi_gpio(spi)->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_cansleep(SPI_SCK_GPIO, is_on);
}
static inline void setmosi(const struct spi_device *spi, int is_on)
{
gpio_set_value_cansleep(SPI_MOSI_GPIO, is_on);
}
static inline int getmiso(const struct spi_device *spi)
{
return !!gpio_get_value_cansleep(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)
{
struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
unsigned int cs = spi_gpio->cs_gpios[spi->chip_select];
/* 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_cansleep(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
}
}
static int spi_gpio_setup(struct spi_device *spi)
{
unsigned int cs;
int status = 0;
struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
struct device_node *np = spi->master->dev.of_node;
if (np) {
/*
* In DT environments, the CS GPIOs have already been
* initialized from the "cs-gpios" property of the node.
*/
cs = spi_gpio->cs_gpios[spi->chip_select];
} else {
/*
* ... otherwise, take it from spi->controller_data
*/
cs = (unsigned int)(uintptr_t) spi->controller_data;
}
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) {
/* in case it was initialized from static board data */
spi_gpio->cs_gpios[spi->chip_select] = cs;
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)
{
struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
unsigned int cs = spi_gpio->cs_gpios[spi->chip_select];
if (cs != SPI_GPIO_NO_CHIPSELECT)
gpio_free(cs);
spi_bitbang_cleanup(spi);
}
static in
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