linux/drivers/spi/spi-gpio.c
Kris Bahnsen 3a6f994f84
spi: spi-gpio: Don't set MOSI as an input if not 3WIRE mode
The addition of 3WIRE support would affect MOSI direction even
when still in standard (4 wire) mode. This can lead to MOSI being
at an invalid logic level when a device driver sets an SPI
message with a NULL tx_buf.

spi.h states that if tx_buf is NULL then "zeros will be shifted
out ... " If MOSI is tristated then the data shifted out is subject
to pull resistors, keepers, or in the absence of those, noise.

This issue came to light when using spi-gpio connected to an
ADS7843 touchscreen controller. MOSI pulled high when clocking
MISO data in caused the SPI device to interpret this as a command
which would put the device in an unexpected and non-functional
state.

Fixes: 4b859db2c6 ("spi: spi-gpio: add SPI_3WIRE support")
Fixes: 5132b3d283 ("spi: gpio: Support 3WIRE high-impedance turn-around")
Signed-off-by: Kris Bahnsen <kris@embeddedTS.com>
Link: https://lore.kernel.org/r/20221207230853.6174-1-kris@embeddedTS.com
Signed-off-by: Mark Brown <broonie@kernel.org>
2022-12-08 11:46:41 +00:00

475 lines
14 KiB
C

// SPDX-License-Identifier: GPL-2.0-or-later
/*
* SPI master driver using generic bitbanged GPIO
*
* Copyright (C) 2006,2008 David Brownell
* Copyright (C) 2017 Linus Walleij
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/gpio/consumer.h>
#include <linux/of.h>
#include <linux/of_device.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->master->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_master_get_devdata(spi->master);
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_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)
{
flags = spi->master->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->master->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->master->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->master->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->chip_select];
/* SPI chip selects are normally active-low */
gpiod_set_value_cansleep(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
}
}
static int spi_gpio_setup(struct spi_device *spi)
{
struct gpio_desc *cs;
int status = 0;
struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
/*
* The CS GPIOs have already been
* initialized from the descriptor lookup.
*/
if (spi_gpio->cs_gpios) {
cs = spi_gpio->cs_gpios[spi->chip_select];
if (!spi->controller_state && cs)
status = gpiod_direction_output(cs,
!(spi->mode & SPI_CS_HIGH));
}
if (!status)
status = spi_bitbang_setup(spi);
return status;
}
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 slave "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);
}
#ifdef CONFIG_OF
static const struct of_device_id spi_gpio_dt_ids[] = {
{ .compatible = "spi-gpio" },
{}
};
MODULE_DEVICE_TABLE(of, spi_gpio_dt_ids);
static int spi_gpio_probe_dt(struct platform_device *pdev,
struct spi_master *master)
{
master->dev.of_node = pdev->dev.of_node;
master->use_gpio_descriptors = true;
return 0;
}
#else
static inline int spi_gpio_probe_dt(struct platform_device *pdev,
struct spi_master *master)
{
return 0;
}
#endif
static int spi_gpio_probe_pdata(struct platform_device *pdev,
struct spi_master *master)
{
struct device *dev = &pdev->dev;
struct spi_gpio_platform_data *pdata = dev_get_platdata(dev);
struct spi_gpio *spi_gpio = spi_master_get_devdata(master);
int i;
#ifdef GENERIC_BITBANG
if (!pdata || !pdata->num_chipselect)
return -ENODEV;
#endif
/*
* The master needs to think there is a chipselect even if not
* connected
*/
master->num_chipselect = pdata->num_chipselect ?: 1;
spi_gpio->cs_gpios = devm_kcalloc(dev, master->num_chipselect,
sizeof(*spi_gpio->cs_gpios),
GFP_KERNEL);
if (!spi_gpio->cs_gpios)
return -ENOMEM;
for (i = 0; i < master->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_master *master;
struct spi_gpio *spi_gpio;
struct device *dev = &pdev->dev;
struct spi_bitbang *bb;
master = devm_spi_alloc_master(dev, sizeof(*spi_gpio));
if (!master)
return -ENOMEM;
if (pdev->dev.of_node)
status = spi_gpio_probe_dt(pdev, master);
else
status = spi_gpio_probe_pdata(pdev, master);
if (status)
return status;
spi_gpio = spi_master_get_devdata(master);
status = spi_gpio_request(dev, spi_gpio);
if (status)
return status;
master->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32);
master->mode_bits = SPI_3WIRE | SPI_3WIRE_HIZ | SPI_CPHA | SPI_CPOL |
SPI_CS_HIGH | SPI_LSB_FIRST;
if (!spi_gpio->mosi) {
/* HW configuration without MOSI pin
*
* No setting SPI_MASTER_NO_RX here - if there is only
* a MOSI pin connected the host can still do RX by
* changing the direction of the line.
*/
master->flags = SPI_MASTER_NO_TX;
}
master->bus_num = pdev->id;
master->setup = spi_gpio_setup;
master->cleanup = spi_gpio_cleanup;
bb = &spi_gpio->bitbang;
bb->master = master;
/*
* 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.
*/
master->flags |= SPI_MASTER_GPIO_SS;
bb->chipselect = spi_gpio_chipselect;
bb->set_line_direction = spi_gpio_set_direction;
if (master->flags & SPI_MASTER_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_master(&pdev->dev, master);
}
MODULE_ALIAS("platform:" DRIVER_NAME);
static struct platform_driver spi_gpio_driver = {
.driver = {
.name = DRIVER_NAME,
.of_match_table = of_match_ptr(spi_gpio_dt_ids),
},
.probe = spi_gpio_probe,
};
module_platform_driver(spi_gpio_driver);
MODULE_DESCRIPTION("SPI master driver using generic bitbanged GPIO ");
MODULE_AUTHOR("David Brownell");
MODULE_LICENSE("GPL");