// SPDX-License-Identifier: GPL-2.0-or-later /* * polling/bitbanging SPI master controller driver utilities */ #include <linux/spinlock.h> #include <linux/workqueue.h> #include <linux/interrupt.h> #include <linux/module.h> #include <linux/delay.h> #include <linux/errno.h> #include <linux/platform_device.h> #include <linux/slab.h> #include <linux/spi/spi.h> #include <linux/spi/spi_bitbang.h> #define SPI_BITBANG_CS_DELAY 100 /*----------------------------------------------------------------------*/ /* * FIRST PART (OPTIONAL): word-at-a-time spi_transfer support. * Use this for GPIO or shift-register level hardware APIs. * * spi_bitbang_cs is in spi_device->controller_state, which is unavailable * to glue code. These bitbang setup() and cleanup() routines are always * used, though maybe they're called from controller-aware code. * * chipselect() and friends may use spi_device->controller_data and * controller registers as appropriate. * * * NOTE: SPI controller pins can often be used as GPIO pins instead, * which means you could use a bitbang driver either to get hardware * working quickly, or testing for differences that aren't speed related. */ struct spi_bitbang_cs { unsigned nsecs; /* (clock cycle time)/2 */ u32 (*txrx_word)(struct spi_device *spi, unsigned nsecs, u32 word, u8 bits, unsigned flags); unsigned (*txrx_bufs)(struct spi_device *, u32 (*txrx_word)( struct spi_device *spi, unsigned nsecs, u32 word, u8 bits, unsigned flags), unsigned, struct spi_transfer *, unsigned); }; static unsigned bitbang_txrx_8( struct spi_device *spi, u32 (*txrx_word)(struct spi_device *spi, unsigned nsecs, u32 word, u8 bits, unsigned flags), unsigned ns, struct spi_transfer *t, unsigned flags ) { unsigned bits = t->bits_per_word; unsigned count = t->len; const u8 *tx = t->tx_buf; u8 *rx = t->rx_buf; while (likely(count > 0)) { u8 word = 0; if (tx) word = *tx++; word = txrx_word(spi, ns, word, bits, flags); if (rx) *rx++ = word; count -= 1; } return t->len - count; } static unsigned bitbang_txrx_16( struct spi_device *spi, u32 (*txrx_word)(struct spi_device *spi, unsigned nsecs, u32 word, u8 bits, unsigned flags), unsigned ns, struct spi_transfer *t, unsigned flags ) { unsigned bits = t->bits_per_word; unsigned count = t->len; const u16 *tx = t->tx_buf; u16 *rx = t->rx_buf; while (likely(count > 1)) { u16 word = 0; if (tx) word = *tx++; word = txrx_word(spi, ns, word, bits, flags); if (rx) *rx++ = word; count -= 2; } return t->len - count; } static unsigned bitbang_txrx_32( struct spi_device *spi, u32 (*txrx_word)(struct spi_device *spi, unsigned nsecs, u32 word, u8 bits, unsigned flags), unsigned ns, struct spi_transfer *t, unsigned flags ) { unsigned bits = t->bits_per_word; unsigned count = t->len; const u32 *tx = t->tx_buf; u32 *rx = t->rx_buf; while (likely(count > 3)) { u32 word = 0; if (tx) word = *tx++; word = txrx_word(spi, ns, word, bits, flags); if (rx) *rx++ = word; count -= 4; } return t->len - count; } int spi_bitbang_setup_transfer(struct spi_device *spi, struct spi_transfer *t) { struct spi_bitbang_cs *cs = spi->controller_state; u8 bits_per_word; u32 hz; if (t) { bits_per_word = t->bits_per_word; hz = t->speed_hz; } else { bits_per_word = 0; hz = 0; } /* spi_transfer level calls that work per-word */ if (!bits_per_word) bits_per_word = spi->bits_per_word; if (bits_per_word <= 8) cs->txrx_bufs = bitbang_txrx_8; else if (bits_per_word <= 16) cs->txrx_bufs = bitbang_txrx_16; else if (bits_per_word <= 32) cs->txrx_bufs = bitbang_txrx_32; else return -EINVAL; /* nsecs = (clock period)/2 */ if (!hz) hz = spi->max_speed_hz; if (hz) { cs->nsecs = (1000000000/2) / hz; if (cs->nsecs > (MAX_UDELAY_MS * 1000 * 1000)) return -EINVAL; } return 0; } EXPORT_SYMBOL_GPL(spi_bitbang_setup_transfer); /* * spi_bitbang_setup - default setup for per-word I/O loops */ int spi_bitbang_setup(struct spi_device *spi) { struct spi_bitbang_cs *cs = spi->controller_state; struct spi_bitbang *bitbang; bool initial_setup = false; int retval; bitbang = spi_master_get_devdata(spi->master); if (!cs) { cs = kzalloc(sizeof(*cs), GFP_KERNEL); if (!cs) return -ENOMEM; spi->controller_state = cs; initial_setup = true; } /* per-word shift register access, in hardware or bitbanging */ cs->txrx_word = bitbang->txrx_word[spi->mode & (SPI_CPOL|SPI_CPHA)]; if (!cs->txrx_word) { retval = -EINVAL; goto err_free; } if (bitbang->setup_transfer) { retval = bitbang->setup_transfer(spi, NULL); if (retval < 0) goto err_free; } dev_dbg(&spi->dev, "%s, %u nsec/bit\n", __func__, 2 * cs->nsecs); return 0; err_free: if (initial_setup) kfree(cs); return retval; } EXPORT_SYMBOL_GPL(spi_bitbang_setup); /* * spi_bitbang_cleanup - default cleanup for per-word I/O loops */ void spi_bitbang_cleanup(struct spi_device *spi) { kfree(spi->controller_state); } EXPORT_SYMBOL_GPL(spi_bitbang_cleanup); static int spi_bitbang_bufs(struct spi_device *spi, struct spi_transfer *t) { struct spi_bitbang_cs *cs = spi->controller_state; unsigned nsecs = cs->nsecs; struct spi_bitbang *bitbang; bitbang = spi_master_get_devdata(spi->master); if (bitbang->set_line_direction) { int err; err = bitbang->set_line_direction(spi, !!(t->tx_buf)); if (err < 0) return err; } if (spi->mode & SPI_3WIRE) { unsigned flags; flags = t->tx_buf ? SPI_MASTER_NO_RX : SPI_MASTER_NO_TX; return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, flags); } return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, 0); } /*----------------------------------------------------------------------*/ /* * SECOND PART ... simple transfer queue runner. * * This costs a task context per controller, running the queue by * performing each transfer in sequence. Smarter hardware can queue * several DMA transfers at once, and process several controller queues * in parallel; this driver doesn't match such hardware very well. * * Drivers can provide word-at-a-time i/o primitives, or provide * transfer-at-a-time ones to leverage dma or fifo hardware. */ static int spi_bitbang_prepare_hardware(struct spi_master *spi) { struct spi_bitbang *bitbang; bitbang = spi_master_get_devdata(spi); mutex_lock(&bitbang->lock); bitbang->busy = 1; mutex_unlock(&bitbang->lock); return 0; } static int spi_bitbang_transfer_one(struct spi_master *master, struct spi_device *spi, struct spi_transfer *transfer) { struct spi_bitbang *bitbang = spi_master_get_devdata(master); int status = 0; if (bitbang->setup_transfer) { status = bitbang->setup_transfer(spi, transfer); if (status < 0) goto out; } if (transfer->len) status = bitbang->txrx_bufs(spi, transfer); if (status == transfer->len) status = 0; else if (status >= 0) status = -EREMOTEIO; out: spi_finalize_current_transfer(master); return status; } static int spi_bitbang_unprepare_hardware(struct spi_master *spi) { struct spi_bitbang *bitbang; bitbang = spi_master_get_devdata(spi); mutex_lock(&bitbang->lock); bitbang->busy = 0; mutex_unlock(&bitbang->lock); return 0; } static void spi_bitbang_set_cs(struct spi_device *spi, bool enable) { struct spi_bitbang *bitbang = spi_master_get_devdata(spi->master); /* SPI core provides CS high / low, but bitbang driver * expects CS active * spi device driver takes care of handling SPI_CS_HIGH */ enable = (!!(spi->mode & SPI_CS_HIGH) == enable); ndelay(SPI_BITBANG_CS_DELAY); bitbang->chipselect(spi, enable ? BITBANG_CS_ACTIVE : BITBANG_CS_INACTIVE); ndelay(SPI_BITBANG_CS_DELAY); } /*----------------------------------------------------------------------*/ int spi_bitbang_init(struct spi_bitbang *bitbang) { struct spi_master *master = bitbang->master; bool custom_cs; if (!master) return -EINVAL; /* * We only need the chipselect callback if we are actually using it. * If we just use GPIO descriptors, it is surplus. If the * SPI_MASTER_GPIO_SS flag is set, we always need to call the * driver-specific chipselect routine. */ custom_cs = (!master->use_gpio_descriptors || (master->flags & SPI_MASTER_GPIO_SS)); if (custom_cs && !bitbang->chipselect) return -EINVAL; mutex_init(&bitbang->lock); if (!master->mode_bits) master->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags; if (master->transfer || master->transfer_one_message) return -EINVAL; master->prepare_transfer_hardware = spi_bitbang_prepare_hardware; master->unprepare_transfer_hardware = spi_bitbang_unprepare_hardware; master->transfer_one = spi_bitbang_transfer_one; /* * When using GPIO descriptors, the ->set_cs() callback doesn't even * get called unless SPI_MASTER_GPIO_SS is set. */ if (custom_cs) master->set_cs = spi_bitbang_set_cs; if (!bitbang->txrx_bufs) { bitbang->use_dma = 0; bitbang->txrx_bufs = spi_bitbang_bufs; if (!master->setup) { if (!bitbang->setup_transfer) bitbang->setup_transfer = spi_bitbang_setup_transfer; master->setup = spi_bitbang_setup; master->cleanup = spi_bitbang_cleanup; } } return 0; } EXPORT_SYMBOL_GPL(spi_bitbang_init); /** * spi_bitbang_start - start up a polled/bitbanging SPI master driver * @bitbang: driver handle * * Caller should have zero-initialized all parts of the structure, and then * provided callbacks for chip selection and I/O loops. If the master has * a transfer method, its final step should call spi_bitbang_transfer; or, * that's the default if the transfer routine is not initialized. It should * also set up the bus number and number of chipselects. * * For i/o loops, provide callbacks either per-word (for bitbanging, or for * hardware that basically exposes a shift register) or per-spi_transfer * (which takes better advantage of hardware like fifos or DMA engines). * * Drivers using per-word I/O loops should use (or call) spi_bitbang_setup, * spi_bitbang_cleanup and spi_bitbang_setup_transfer to handle those spi * master methods. Those methods are the defaults if the bitbang->txrx_bufs * routine isn't initialized. * * This routine registers the spi_master, which will process requests in a * dedicated task, keeping IRQs unblocked most of the time. To stop * processing those requests, call spi_bitbang_stop(). * * On success, this routine will take a reference to master. The caller is * responsible for calling spi_bitbang_stop() to decrement the reference and * spi_master_put() as counterpart of spi_alloc_master() to prevent a memory * leak. */ int spi_bitbang_start(struct spi_bitbang *bitbang) { struct spi_master *master = bitbang->master; int ret; ret = spi_bitbang_init(bitbang); if (ret) return ret; /* driver may get busy before register() returns, especially * if someone registered boardinfo for devices */ ret = spi_register_master(spi_master_get(master)); if (ret) spi_master_put(master); return ret; } EXPORT_SYMBOL_GPL(spi_bitbang_start); /* * spi_bitbang_stop - stops the task providing spi communication */ void spi_bitbang_stop(struct spi_bitbang *bitbang) { spi_unregister_master(bitbang->master); } EXPORT_SYMBOL_GPL(spi_bitbang_stop); MODULE_LICENSE("GPL");