// SPDX-License-Identifier: GPL-2.0-or-later
/*
* SPI host driver using generic bitbanged GPIO
*
* Copyright (C) 2006,2008 David Brownell
* Copyright (C) 2017 Linus Walleij
*/
#include <linux/gpio/consumer.h>
#include <linux/kernel.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/property.h>
#include <linux/spi/spi.h>
#include <linux/spi/spi_bitbang.h>
#include <linux/spi/spi_gpio.h>
/*
* This bitbanging SPI host 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->dev.driver_data ... points to spi_gpio->bitbang
*/
struct spi_gpio {
struct spi_bitbang bitbang;
struct gpio_desc *sck;
struct gpio_desc *miso;
struct gpio_desc *mosi;
struct gpio_desc **cs_gpios;
};
/*----------------------------------------------------------------------*/
/*
* 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 */
#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_controller_get_devdata(spi->controller);
spi_gpio = container_of(bang, struct spi_gpio, bitbang);
return spi_gpio;
}
/* These helpers are in turn called by the bitbang inlines */
static inline void setsck(const struct spi_device *spi, int is_on)
{
struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
gpiod_set_value_cansleep(spi_gpio->sck, is_on);
}
static inline void setmosi(const struct spi_device *spi, int is_on)
{
struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
gpiod_set_value_cansleep(spi_gpio->mosi, is_on);
}
static inline int getmiso(const struct spi_device *spi)
{
struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
if (spi->mode & SPI_3WIRE)
return !!gpiod_get_value_cansleep(spi_gpio->mosi);
else
return !!gpiod_get_value_cansleep(spi_gpio->miso);
}
/*
* 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, unsigned flags)
{
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha0(spi, nsecs, 0, flags, word, bits);
else
return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
}
static u32 spi_gpio_txrx_word_mode1(struct spi_device *spi,
unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha1(spi, nsecs, 0, flags, word, bits);
else
return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
}
static u32 spi_gpio_txrx_word_mode2(struct spi_device *spi,
unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha0(spi, nsecs, 1, flags, word, bits);
else
return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
}
static u32 spi_gpio_txrx_word_mode3(struct spi_device *spi,
unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha1(spi, nsecs, 1, flags, word, bits);
else
return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
}
/*
* These functions do not call setmosi or getmiso if respective flag
* (SPI_CONTROLLER_NO_RX or SPI_CONTROLLER_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)
{
flags = spi->controller->flags;
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha0(spi, nsecs, 0, flags, word, bits);
else
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)
{
flags = spi->controller->flags;
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha1(spi, nsecs, 0, flags, word, bits);
else
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)
{
flags = spi->controller->flags;
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha0(spi, nsecs, 1, flags, word, bits);
else
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)
{
flags = spi->controller->flags;
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha1(spi, nsecs, 1, flags, word, bits);
else
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);
/* set initial clock line level */
if (is_active)
gpiod_set_value_cansleep(spi_gpio->sck, spi->mode & SPI_CPOL);
/* Drive chip select line, if we have one */
if (spi_gpio->cs_gpios) {
struct gpio_desc *cs = spi_gpio->cs_gpios[spi_get_chipselect(spi, 0)];
/* SPI chip selects are normally active-low */
gpiod_set_value_cansleep(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
}
}
static void spi_gpio_set_mosi_idle(struct spi_device *spi)
{
struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
gpiod_set_value_cansleep(spi_gpio->mosi,
!!(spi->mode & SPI_MOSI_IDLE_HIGH));
}
static int spi_gpio_setup(struct spi_device *spi)
{
struct gpio_desc *cs;
struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
int ret;
/*
* The CS GPIOs have already been
* initialized from the descriptor lookup.
*/
if (spi_gpio->cs_gpios) {
cs = spi_gpio->cs_gpios[spi_get_chipselect(spi, 0)];
if (!spi->controller_state && cs) {
ret = gpiod_direction_output(cs, !(spi->mode & SPI_CS_HIGH));
if (ret)
return ret;
}
}
return spi_bitbang_setup(spi);
}
static int spi_gpio_set_direction(struct spi_device *spi, bool output)
{
struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
int ret;
if (output)
return gpiod_direction_output(spi_gpio->mosi, 1);
/*
* Only change MOSI to an input if using 3WIRE mode.
* Otherwise, MOSI could be left floating if there is
* no pull resistor connected to the I/O pin, or could
* be left logic high if there is a pull-up. Transmitting
* logic high when only clocking MISO data in can put some
* SPI devices in to a bad state.
*/
if (spi->mode & SPI_3WIRE) {
ret = gpiod_direction_input(spi_gpio->mosi);
if (ret)
return ret;
}
/*
* Send a turnaround high impedance cycle when switching
* from output to input. Theoretically there should be
* a clock delay here, but as has been noted above, the
* nsec delay function for bit-banged GPIO is simply
* {} because bit-banging just doesn't get fast enough
* anyway.
*/
if (spi->mode & SPI_3WIRE_HIZ) {
gpiod_set_value_cansleep(spi_gpio->sck,
!(spi->mode & SPI_CPOL));
gpiod_set_value_cansleep(spi_gpio->sck,
!!(spi->mode & SPI_CPOL));
}
return 0;
}
static void spi_gpio_cleanup(struct spi_device *spi)
{
spi_bitbang_cleanup(spi);
}
/*
* 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 target "response".)
*/
static int spi_gpio_request(struct device *dev, struct spi_gpio *spi_gpio)
{
spi_gpio->mosi = devm_gpiod_get_optional(dev, "mosi", GPIOD_OUT_LOW);
if (IS_ERR(spi_gpio->mosi))
return PTR_ERR(spi_gpio->mosi);
spi_gpio->miso = devm_gpiod_get_optional(dev, "miso", GPIOD_IN);
if (IS_ERR(spi_gpio->miso))
return PTR_ERR(spi_gpio->miso);
spi_gpio->sck = devm_gpiod_get(dev, "sck", GPIOD_OUT_LOW);
return PTR_ERR_OR_ZERO(spi_gpio->sck);
}
static int spi_gpio_probe_pdata(struct platform_device *pdev,
struct spi_controller *host)
{
struct device *dev = &pdev->dev;
struct spi_gpio_platform_data *pdata = dev_get_platdata(dev);
struct spi_gpio *spi_gpio = spi_controller_get_devdata(host);
int i;
#ifdef GENERIC_BITBANG
if (!pdata || !pdata->num_chipselect)
return -ENODEV;
#endif
/*
* The host needs to think there is a chipselect even if not
* connected
*/
host->num_chipselect = pdata->num_chipselect ?: 1;
spi_gpio->cs_gpios = devm_kcalloc(dev, host->num_chipselect,
sizeof(*spi_gpio->cs_gpios),
GFP_KERNEL);
if (!spi_gpio->cs_gpios)
return -ENOMEM;
for (i = 0; i < host->num_chipselect; i++) {
spi_gpio->cs_gpios[i] = devm_gpiod_get_index(dev, "cs", i,
GPIOD_OUT_HIGH);
if (IS_ERR(spi_gpio->cs_gpios[i]))
return PTR_ERR(spi_gpio->cs_gpios[i]);
}
return 0;
}
static int spi_gpio_probe(struct platform_device *pdev)
{
int status;
struct spi_controller *host;
struct spi_gpio *spi_gpio;
struct device *dev = &pdev->dev;
struct fwnode_handle *fwnode = dev_fwnode(dev);
struct spi_bitbang *bb;
host = devm_spi_alloc_host(dev, sizeof(*spi_gpio));
if (!host)
return -ENOMEM;
if (fwnode) {
device_set_node(&host->dev, fwnode);
host->use_gpio_descriptors = true;
} else {
status = spi_gpio_probe_pdata(pdev, host);
if (status)
return status;
}
spi_gpio = spi_controller_get_devdata(host);
status = spi_gpio_request(dev, spi_gpio);
if (status)
return status;
host->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32);
host->mode_bits = SPI_3WIRE | SPI_3WIRE_HIZ | SPI_CPHA | SPI_CPOL |
SPI_CS_HIGH | SPI_LSB_FIRST | SPI_MOSI_IDLE_LOW |
SPI_MOSI_IDLE_HIGH;
if (!spi_gpio->mosi) {
/* HW configuration without MOSI pin
*
* No setting SPI_CONTROLLER_NO_RX here - if there is only
* a MOSI pin connected the host can still do RX by
* changing the direction of the line.
*/
host->flags = SPI_CONTROLLER_NO_TX;
}
host->bus_num = pdev->id;
host->setup = spi_gpio_setup;
host->cleanup = spi_gpio_cleanup;
bb = &spi_gpio->bitbang;
bb->ctlr = host;
/*
* There is some additional business, apart from driving the CS GPIO
* line, that we need to do on selection. This makes the local
* callback for chipselect always get called.
*/
host->flags |= SPI_CONTROLLER_GPIO_SS;
bb->chipselect = spi_gpio_chipselect;
bb->set_line_direction = spi_gpio_set_direction;
bb->set_mosi_idle = spi_gpio_set_mosi_idle;
if (host->flags & SPI_CONTROLLER_NO_TX) {
bb->txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0;
bb->txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1;
bb->txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2;
bb->txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3;
} else {
bb->txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
bb->txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
bb->txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;
bb->txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;
}
bb->setup_transfer = spi_bitbang_setup_transfer;
status = spi_bitbang_init(&spi_gpio->bitbang);
if (status)
return status;
return devm_spi_register_controller(&pdev->dev, host);
}
MODULE_ALIAS("platform:" DRIVER_NAME);
static const struct of_device_id spi_gpio_dt_ids[] = {
{ .compatible = "spi-gpio" },
{}
};
MODULE_DEVICE_TABLE(of, spi_gpio_dt_ids);
static struct platform_driver spi_gpio_driver = {
.driver = {
.name = DRIVER_NAME,
.of_match_table = spi_gpio_dt_ids,
},
.probe = spi_gpio_probe,
};
module_platform_driver(spi_gpio_driver);
MODULE_DESCRIPTION("SPI host driver using generic bitbanged GPIO ");
MODULE_AUTHOR("David Brownell");
MODULE_LICENSE("GPL");
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