// SPDX-License-Identifier: GPL-2.0-or-later /* * Driver for Broadcom BCM2835 SPI Controllers * * Copyright (C) 2012 Chris Boot * Copyright (C) 2013 Stephen Warren * Copyright (C) 2015 Martin Sperl * * This driver is inspired by: * spi-ath79.c, Copyright (C) 2009-2011 Gabor Juhos * spi-atmel.c, Copyright (C) 2006 Atmel Corporation */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* FIXME: using GPIO lookup tables */ #include #include #include #include /* SPI register offsets */ #define BCM2835_SPI_CS 0x00 #define BCM2835_SPI_FIFO 0x04 #define BCM2835_SPI_CLK 0x08 #define BCM2835_SPI_DLEN 0x0c #define BCM2835_SPI_LTOH 0x10 #define BCM2835_SPI_DC 0x14 /* Bitfields in CS */ #define BCM2835_SPI_CS_LEN_LONG 0x02000000 #define BCM2835_SPI_CS_DMA_LEN 0x01000000 #define BCM2835_SPI_CS_CSPOL2 0x00800000 #define BCM2835_SPI_CS_CSPOL1 0x00400000 #define BCM2835_SPI_CS_CSPOL0 0x00200000 #define BCM2835_SPI_CS_RXF 0x00100000 #define BCM2835_SPI_CS_RXR 0x00080000 #define BCM2835_SPI_CS_TXD 0x00040000 #define BCM2835_SPI_CS_RXD 0x00020000 #define BCM2835_SPI_CS_DONE 0x00010000 #define BCM2835_SPI_CS_LEN 0x00002000 #define BCM2835_SPI_CS_REN 0x00001000 #define BCM2835_SPI_CS_ADCS 0x00000800 #define BCM2835_SPI_CS_INTR 0x00000400 #define BCM2835_SPI_CS_INTD 0x00000200 #define BCM2835_SPI_CS_DMAEN 0x00000100 #define BCM2835_SPI_CS_TA 0x00000080 #define BCM2835_SPI_CS_CSPOL 0x00000040 #define BCM2835_SPI_CS_CLEAR_RX 0x00000020 #define BCM2835_SPI_CS_CLEAR_TX 0x00000010 #define BCM2835_SPI_CS_CPOL 0x00000008 #define BCM2835_SPI_CS_CPHA 0x00000004 #define BCM2835_SPI_CS_CS_10 0x00000002 #define BCM2835_SPI_CS_CS_01 0x00000001 #define BCM2835_SPI_FIFO_SIZE 64 #define BCM2835_SPI_FIFO_SIZE_3_4 48 #define BCM2835_SPI_DMA_MIN_LENGTH 96 #define BCM2835_SPI_MODE_BITS (SPI_CPOL | SPI_CPHA | SPI_CS_HIGH \ | SPI_NO_CS | SPI_3WIRE) #define DRV_NAME "spi-bcm2835" /* define polling limits */ static unsigned int polling_limit_us = 30; module_param(polling_limit_us, uint, 0664); MODULE_PARM_DESC(polling_limit_us, "time in us to run a transfer in polling mode\n"); /** * struct bcm2835_spi - BCM2835 SPI controller * @regs: base address of register map * @clk: core clock, divided to calculate serial clock * @cs_gpio: chip-select GPIO descriptor * @clk_hz: core clock cached speed * @irq: interrupt, signals TX FIFO empty or RX FIFO ¾ full * @tfr: SPI transfer currently processed * @ctlr: SPI controller reverse lookup * @tx_buf: pointer whence next transmitted byte is read * @rx_buf: pointer where next received byte is written * @tx_len: remaining bytes to transmit * @rx_len: remaining bytes to receive * @tx_prologue: bytes transmitted without DMA if first TX sglist entry's * length is not a multiple of 4 (to overcome hardware limitation) * @rx_prologue: bytes received without DMA if first RX sglist entry's * length is not a multiple of 4 (to overcome hardware limitation) * @tx_spillover: whether @tx_prologue spills over to second TX sglist entry * @debugfs_dir: the debugfs directory - neede to remove debugfs when * unloading the module * @count_transfer_polling: count of how often polling mode is used * @count_transfer_irq: count of how often interrupt mode is used * @count_transfer_irq_after_polling: count of how often we fall back to * interrupt mode after starting in polling mode. * These are counted as well in @count_transfer_polling and * @count_transfer_irq * @count_transfer_dma: count how often dma mode is used * @target: SPI target currently selected * (used by bcm2835_spi_dma_tx_done() to write @clear_rx_cs) * @tx_dma_active: whether a TX DMA descriptor is in progress * @rx_dma_active: whether a RX DMA descriptor is in progress * (used by bcm2835_spi_dma_tx_done() to handle a race) * @fill_tx_desc: preallocated TX DMA descriptor used for RX-only transfers * (cyclically copies from zero page to TX FIFO) * @fill_tx_addr: bus address of zero page */ struct bcm2835_spi { void __iomem *regs; struct clk *clk; struct gpio_desc *cs_gpio; unsigned long clk_hz; int irq; struct spi_transfer *tfr; struct spi_controller *ctlr; const u8 *tx_buf; u8 *rx_buf; int tx_len; int rx_len; int tx_prologue; int rx_prologue; unsigned int tx_spillover; struct dentry *debugfs_dir; u64 count_transfer_polling; u64 count_transfer_irq; u64 count_transfer_irq_after_polling; u64 count_transfer_dma; struct bcm2835_spidev *target; unsigned int tx_dma_active; unsigned int rx_dma_active; struct dma_async_tx_descriptor *fill_tx_desc; dma_addr_t fill_tx_addr; }; /** * struct bcm2835_spidev - BCM2835 SPI target * @prepare_cs: precalculated CS register value for ->prepare_message() * (uses target-specific clock polarity and phase settings) * @clear_rx_desc: preallocated RX DMA descriptor used for TX-only transfers * (cyclically clears RX FIFO by writing @clear_rx_cs to CS register) * @clear_rx_addr: bus address of @clear_rx_cs * @clear_rx_cs: precalculated CS register value to clear RX FIFO * (uses target-specific clock polarity and phase settings) */ struct bcm2835_spidev { u32 prepare_cs; struct dma_async_tx_descriptor *clear_rx_desc; dma_addr_t clear_rx_addr; u32 clear_rx_cs ____cacheline_aligned; }; #if defined(CONFIG_DEBUG_FS) static void bcm2835_debugfs_create(struct bcm2835_spi *bs, const char *dname) { char name[64]; struct dentry *dir; /* get full name */ snprintf(name, sizeof(name), "spi-bcm2835-%s", dname); /* the base directory */ dir = debugfs_create_dir(name, NULL); bs->debugfs_dir = dir; /* the counters */ debugfs_create_u64("count_transfer_polling", 0444, dir, &bs->count_transfer_polling); debugfs_create_u64("count_transfer_irq", 0444, dir, &bs->count_transfer_irq); debugfs_create_u64("count_transfer_irq_after_polling", 0444, dir, &bs->count_transfer_irq_after_polling); debugfs_create_u64("count_transfer_dma", 0444, dir, &bs->count_transfer_dma); } static void bcm2835_debugfs_remove(struct bcm2835_spi *bs) { debugfs_remove_recursive(bs->debugfs_dir); bs->debugfs_dir = NULL; } #else static void bcm2835_debugfs_create(struct bcm2835_spi *bs, const char *dname) { } static void bcm2835_debugfs_remove(struct bcm2835_spi *bs) { } #endif /* CONFIG_DEBUG_FS */ static inline u32 bcm2835_rd(struct bcm2835_spi *bs, unsigned int reg) { return readl(bs->regs + reg); } static inline void bcm2835_wr(struct bcm2835_spi *bs, unsigned int reg, u32 val) { writel(val, bs->regs + reg); } static inline void bcm2835_rd_fifo(struct bcm2835_spi *bs) { u8 byte; while ((bs->rx_len) && (bcm2835_rd(bs, BCM2835_SPI_CS) & BCM2835_SPI_CS_RXD)) { byte = bcm2835_rd(bs, BCM2835_SPI_FIFO); if (bs->rx_buf) *bs->rx_buf++ = byte; bs->rx_len--; } } static inline void bcm2835_wr_fifo(struct bcm2835_spi *bs) { u8 byte; while ((bs->tx_len) && (bcm2835_rd(bs, BCM2835_SPI_CS) & BCM2835_SPI_CS_TXD)) { byte = bs->tx_buf ? *bs->tx_buf++ : 0; bcm2835_wr(bs, BCM2835_SPI_FIFO, byte); bs->tx_len--; } } /** * bcm2835_rd_fifo_count() - blindly read exactly @count bytes from RX FIFO * @bs: BCM2835 SPI controller * @count: bytes to read from RX FIFO * * The caller must ensure that @bs->rx_len is greater than or equal to @count, * that the RX FIFO contains at least @count bytes and that the DMA Enable flag * in the CS register is set (such that a read from the FIFO register receives * 32-bit instead of just 8-bit). Moreover @bs->rx_buf must not be %NULL. */ static inline void bcm2835_rd_fifo_count(struct bcm2835_spi *bs, int count) { u32 val; int len; bs->rx_len -= count; do { val = bcm2835_rd(bs, BCM2835_SPI_FIFO); len = min(count, 4); memcpy(bs->rx_buf, &val, len); bs->rx_buf += len; count -= 4; } while (count > 0); } /** * bcm2835_wr_fifo_count() - blindly write exactly @count bytes to TX FIFO * @bs: BCM2835 SPI controller * @count: bytes to write to TX FIFO * * The caller must ensure that @bs->tx_len is greater than or equal to @count, * that the TX FIFO can accommodate @count bytes and that the DMA Enable flag * in the CS register is set (such that a write to the FIFO register transmits * 32-bit instead of just 8-bit). */ static inline void bcm2835_wr_fifo_count(struct bcm2835_spi *bs, int count) { u32 val; int len; bs->tx_len -= count; do { if (bs->tx_buf) { len = min(count, 4); memcpy(&val, bs->tx_buf, len); bs->tx_buf += len; } else { val = 0; } bcm2835_wr(bs, BCM2835_SPI_FIFO, val); count -= 4; } while (count > 0); } /** * bcm2835_wait_tx_fifo_empty() - busy-wait for TX FIFO to empty * @bs: BCM2835 SPI controller * * The caller must ensure that the RX FIFO can accommodate as many bytes * as have been written to the TX FIFO: Transmission is halted once the * RX FIFO is full, causing this function to spin forever. */ static inline void bcm2835_wait_tx_fifo_empty(struct bcm2835_spi *bs) { while (!(bcm2835_rd(bs, BCM2835_SPI_CS) & BCM2835_SPI_CS_DONE)) cpu_relax(); } /** * bcm2835_rd_fifo_blind() - blindly read up to @count bytes from RX FIFO * @bs: BCM2835 SPI controller * @count: bytes available for reading in RX FIFO */ static inline void bcm2835_rd_fifo_blind(struct bcm2835_spi *bs, int count) { u8 val; count = min(count, bs->rx_len); bs->rx_len -= count; do { val = bcm2835_rd(bs, BCM2835_SPI_FIFO); if (bs->rx_buf) *bs->rx_buf++ = val; } while (--count); } /** * bcm2835_wr_fifo_blind() - blindly write up to @count bytes to TX FIFO * @bs: BCM2835 SPI controller * @count: bytes available for writing in TX FIFO */ static inline void bcm2835_wr_fifo_blind(struct bcm2835_spi *bs, int count) { u8 val; count = min(count, bs->tx_len); bs->tx_len -= count; do { val = bs->tx_buf ? *bs->tx_buf++ : 0; bcm2835_wr(bs, BCM2835_SPI_FIFO, val); } while (--count); } static void bcm2835_spi_reset_hw(struct bcm2835_spi *bs) { u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS); /* Disable SPI interrupts and transfer */ cs &= ~(BCM2835_SPI_CS_INTR | BCM2835_SPI_CS_INTD | BCM2835_SPI_CS_DMAEN | BCM2835_SPI_CS_TA); /* * Transmission sometimes breaks unless the DONE bit is written at the * end of every transfer. The spec says it's a RO bit. Either the * spec is wrong and the bit is actually of type RW1C, or it's a * hardware erratum. */ cs |= BCM2835_SPI_CS_DONE; /* and reset RX/TX FIFOS */ cs |= BCM2835_SPI_CS_CLEAR_RX | BCM2835_SPI_CS_CLEAR_TX; /* and reset the SPI_HW */ bcm2835_wr(bs, BCM2835_SPI_CS, cs); /* as well as DLEN */ bcm2835_wr(bs, BCM2835_SPI_DLEN, 0); } static irqreturn_t bcm2835_spi_interrupt(int irq, void *dev_id) { struct bcm2835_spi *bs = dev_id; u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS); /* Bail out early if interrupts are not enabled */ if (!(cs & BCM2835_SPI_CS_INTR)) return IRQ_NONE; /* * An interrupt is signaled either if DONE is set (TX FIFO empty) * or if RXR is set (RX FIFO >= ¾ full). */ if (cs & BCM2835_SPI_CS_RXF) bcm2835_rd_fifo_blind(bs, BCM2835_SPI_FIFO_SIZE); else if (cs & BCM2835_SPI_CS_RXR) bcm2835_rd_fifo_blind(bs, BCM2835_SPI_FIFO_SIZE_3_4); if (bs->tx_len && cs & BCM2835_SPI_CS_DONE) bcm2835_wr_fifo_blind(bs, BCM2835_SPI_FIFO_SIZE); /* Read as many bytes as possible from FIFO */ bcm2835_rd_fifo(bs); /* Write as many bytes as possible to FIFO */ bcm2835_wr_fifo(bs); if (!bs->rx_len) { /* Transfer complete - reset SPI HW */ bcm2835_spi_reset_hw(bs); /* wake up the framework */ spi_finalize_current_transfer(bs->ctlr); } return IRQ_HANDLED; } static int bcm2835_spi_transfer_one_irq(struct spi_controller *ctlr, struct spi_device *spi, struct spi_transfer *tfr, u32 cs, bool fifo_empty) { struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); /* update usage statistics */ bs->count_transfer_irq++; /* * Enable HW block, but with interrupts still disabled. * Otherwise the empty TX FIFO would immediately trigger an interrupt. */ bcm2835_wr(bs, BCM2835_SPI_CS, cs | BCM2835_SPI_CS_TA); /* fill TX FIFO as much as possible */ if (fifo_empty) bcm2835_wr_fifo_blind(bs, BCM2835_SPI_FIFO_SIZE); bcm2835_wr_fifo(bs); /* enable interrupts */ cs |= BCM2835_SPI_CS_INTR | BCM2835_SPI_CS_INTD | BCM2835_SPI_CS_TA; bcm2835_wr(bs, BCM2835_SPI_CS, cs); /* signal that we need to wait for completion */ return 1; } /** * bcm2835_spi_transfer_prologue() - transfer first few bytes without DMA * @ctlr: SPI host controller * @tfr: SPI transfer * @bs: BCM2835 SPI controller * @cs: CS register * * A limitation in DMA mode is that the FIFO must be accessed in 4 byte chunks. * Only the final write access is permitted to transmit less than 4 bytes, the * SPI controller deduces its intended size from the DLEN register. * * If a TX or RX sglist contains multiple entries, one per page, and the first * entry starts in the middle of a page, that first entry's length may not be * a multiple of 4. Subsequent entries are fine because they span an entire * page, hence do have a length that's a multiple of 4. * * This cannot happen with kmalloc'ed buffers (which is what most clients use) * because they are contiguous in physical memory and therefore not split on * page boundaries by spi_map_buf(). But it *can* happen with vmalloc'ed * buffers. * * The DMA engine is incapable of combining sglist entries into a continuous * stream of 4 byte chunks, it treats every entry separately: A TX entry is * rounded up a to a multiple of 4 bytes by transmitting surplus bytes, an RX * entry is rounded up by throwing away received bytes. * * Overcome this limitation by transferring the first few bytes without DMA: * E.g. if the first TX sglist entry's length is 23 and the first RX's is 42, * write 3 bytes to the TX FIFO but read only 2 bytes from the RX FIFO. * The residue of 1 byte in the RX FIFO is picked up by DMA. Together with * the rest of the first RX sglist entry it makes up a multiple of 4 bytes. * * Should the RX prologue be larger, say, 3 vis-à-vis a TX prologue of 1, * write 1 + 4 = 5 bytes to the TX FIFO and read 3 bytes from the RX FIFO. * Caution, the additional 4 bytes spill over to the second TX sglist entry * if the length of the first is *exactly* 1. * * At most 6 bytes are written and at most 3 bytes read. Do we know the * transfer has this many bytes? Yes, see BCM2835_SPI_DMA_MIN_LENGTH. * * The FIFO is normally accessed with 8-bit width by the CPU and 32-bit width * by the DMA engine. Toggling the DMA Enable flag in the CS register switches * the width but also garbles the FIFO's contents. The prologue must therefore * be transmitted in 32-bit width to ensure that the following DMA transfer can * pick up the residue in the RX FIFO in ungarbled form. */ static void bcm2835_spi_transfer_prologue(struct spi_controller *ctlr, struct spi_transfer *tfr, struct bcm2835_spi *bs, u32 cs) { int tx_remaining; bs->tfr = tfr; bs->tx_prologue = 0; bs->rx_prologue = 0; bs->tx_spillover = false; if (bs->tx_buf && !sg_is_last(&tfr->tx_sg.sgl[0])) bs->tx_prologue = sg_dma_len(&tfr->tx_sg.sgl[0]) & 3; if (bs->rx_buf && !sg_is_last(&tfr->rx_sg.sgl[0])) { bs->rx_prologue = sg_dma_len(&tfr->rx_sg.sgl[0]) & 3; if (bs->rx_prologue > bs->tx_prologue) { if (!bs->tx_buf || sg_is_last(&tfr->tx_sg.sgl[0])) { bs->tx_prologue = bs->rx_prologue; } else { bs->tx_prologue += 4; bs->tx_spillover = !(sg_dma_len(&tfr->tx_sg.sgl[0]) & ~3); } } } /* rx_prologue > 0 implies tx_prologue > 0, so check only the latter */ if (!bs->tx_prologue) return; /* Write and read RX prologue. Adjust first entry in RX sglist. */ if (bs->rx_prologue) { bcm2835_wr(bs, BCM2835_SPI_DLEN, bs->rx_prologue); bcm2835_wr(bs, BCM2835_SPI_CS, cs | BCM2835_SPI_CS_TA | BCM2835_SPI_CS_DMAEN); bcm2835_wr_fifo_count(bs, bs->rx_prologue); bcm2835_wait_tx_fifo_empty(bs); bcm2835_rd_fifo_count(bs, bs->rx_prologue); bcm2835_wr(bs, BCM2835_SPI_CS, cs | BCM2835_SPI_CS_CLEAR_RX | BCM2835_SPI_CS_CLEAR_TX | BCM2835_SPI_CS_DONE); dma_sync_single_for_device(ctlr->dma_rx->device->dev, sg_dma_address(&tfr->rx_sg.sgl[0]), bs->rx_prologue, DMA_FROM_DEVICE); sg_dma_address(&tfr->rx_sg.sgl[0]) += bs->rx_prologue; sg_dma_len(&tfr->rx_sg.sgl[0]) -= bs->rx_prologue; } if (!bs->tx_buf) return; /* * Write remaining TX prologue. Adjust first entry in TX sglist. * Also adjust second entry if prologue spills over to it. */ tx_remaining = bs->tx_prologue - bs->rx_prologue; if (tx_remaining) { bcm2835_wr(bs, BCM2835_SPI_DLEN, tx_remaining); bcm2835_wr(bs, BCM2835_SPI_CS, cs | BCM2835_SPI_CS_TA | BCM2835_SPI_CS_DMAEN); bcm2835_wr_fifo_count(bs, tx_remaining); bcm2835_wait_tx_fifo_empty(bs); bcm2835_wr(bs, BCM2835_SPI_CS, cs | BCM2835_SPI_CS_CLEAR_TX | BCM2835_SPI_CS_DONE); } if (likely(!bs->tx_spillover)) { sg_dma_address(&tfr->tx_sg.sgl[0]) += bs->tx_prologue; sg_dma_len(&tfr->tx_sg.sgl[0]) -= bs->tx_prologue; } else { sg_dma_len(&tfr->tx_sg.sgl[0]) = 0; sg_dma_address(&tfr->tx_sg.sgl[1]) += 4; sg_dma_len(&tfr->tx_sg.sgl[1]) -= 4; } } /** * bcm2835_spi_undo_prologue() - reconstruct original sglist state * @bs: BCM2835 SPI controller * * Undo changes which were made to an SPI transfer's sglist when transmitting * the prologue. This is necessary to ensure the same memory ranges are * unmapped that were originally mapped. */ static void bcm2835_spi_undo_prologue(struct bcm2835_spi *bs) { struct spi_transfer *tfr = bs->tfr; if (!bs->tx_prologue) return; if (bs->rx_prologue) { sg_dma_address(&tfr->rx_sg.sgl[0]) -= bs->rx_prologue; sg_dma_len(&tfr->rx_sg.sgl[0]) += bs->rx_prologue; } if (!bs->tx_buf) goto out; if (likely(!bs->tx_spillover)) { sg_dma_address(&tfr->tx_sg.sgl[0]) -= bs->tx_prologue; sg_dma_len(&tfr->tx_sg.sgl[0]) += bs->tx_prologue; } else { sg_dma_len(&tfr->tx_sg.sgl[0]) = bs->tx_prologue - 4; sg_dma_address(&tfr->tx_sg.sgl[1]) -= 4; sg_dma_len(&tfr->tx_sg.sgl[1]) += 4; } out: bs->tx_prologue = 0; } /** * bcm2835_spi_dma_rx_done() - callback for DMA RX channel * @data: SPI host controller * * Used for bidirectional and RX-only transfers. */ static void bcm2835_spi_dma_rx_done(void *data) { struct spi_controller *ctlr = data; struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); /* terminate tx-dma as we do not have an irq for it * because when the rx dma will terminate and this callback * is called the tx-dma must have finished - can't get to this * situation otherwise... */ dmaengine_terminate_async(ctlr->dma_tx); bs->tx_dma_active = false; bs->rx_dma_active = false; bcm2835_spi_undo_prologue(bs); /* reset fifo and HW */ bcm2835_spi_reset_hw(bs); /* and mark as completed */; spi_finalize_current_transfer(ctlr); } /** * bcm2835_spi_dma_tx_done() - callback for DMA TX channel * @data: SPI host controller * * Used for TX-only transfers. */ static void bcm2835_spi_dma_tx_done(void *data) { struct spi_controller *ctlr = data; struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); /* busy-wait for TX FIFO to empty */ while (!(bcm2835_rd(bs, BCM2835_SPI_CS) & BCM2835_SPI_CS_DONE)) bcm2835_wr(bs, BCM2835_SPI_CS, bs->target->clear_rx_cs); bs->tx_dma_active = false; smp_wmb(); /* * In case of a very short transfer, RX DMA may not have been * issued yet. The onus is then on bcm2835_spi_transfer_one_dma() * to terminate it immediately after issuing. */ if (cmpxchg(&bs->rx_dma_active, true, false)) dmaengine_terminate_async(ctlr->dma_rx); bcm2835_spi_undo_prologue(bs); bcm2835_spi_reset_hw(bs); spi_finalize_current_transfer(ctlr); } /** * bcm2835_spi_prepare_sg() - prepare and submit DMA descriptor for sglist * @ctlr: SPI host controller * @tfr: SPI transfer * @bs: BCM2835 SPI controller * @target: BCM2835 SPI target * @is_tx: whether to submit DMA descriptor for TX or RX sglist * * Prepare and submit a DMA descriptor for the TX or RX sglist of @tfr. * Return 0 on success or a negative error number. */ static int bcm2835_spi_prepare_sg(struct spi_controller *ctlr, struct spi_transfer *tfr, struct bcm2835_spi *bs, struct bcm2835_spidev *target, bool is_tx) { struct dma_chan *chan; struct scatterlist *sgl; unsigned int nents; enum dma_transfer_direction dir; unsigned long flags; struct dma_async_tx_descriptor *desc; dma_cookie_t cookie; if (is_tx) { dir = DMA_MEM_TO_DEV; chan = ctlr->dma_tx; nents = tfr->tx_sg.nents; sgl = tfr->tx_sg.sgl; flags = tfr->rx_buf ? 0 : DMA_PREP_INTERRUPT; } else { dir = DMA_DEV_TO_MEM; chan = ctlr->dma_rx; nents = tfr->rx_sg.nents; sgl = tfr->rx_sg.sgl; flags = DMA_PREP_INTERRUPT; } /* prepare the channel */ desc = dmaengine_prep_slave_sg(chan, sgl, nents, dir, flags); if (!desc) return -EINVAL; /* * Completion is signaled by the RX channel for bidirectional and * RX-only transfers; else by the TX channel for TX-only transfers. */ if (!is_tx) { desc->callback = bcm2835_spi_dma_rx_done; desc->callback_param = ctlr; } else if (!tfr->rx_buf) { desc->callback = bcm2835_spi_dma_tx_done; desc->callback_param = ctlr; bs->target = target; } /* submit it to DMA-engine */ cookie = dmaengine_submit(desc); return dma_submit_error(cookie); } /** * bcm2835_spi_transfer_one_dma() - perform SPI transfer using DMA engine * @ctlr: SPI host controller * @tfr: SPI transfer * @target: BCM2835 SPI target * @cs: CS register * * For *bidirectional* transfers (both tx_buf and rx_buf are non-%NULL), set up * the TX and RX DMA channel to copy between memory and FIFO register. * * For *TX-only* transfers (rx_buf is %NULL), copying the RX FIFO's contents to * memory is pointless. However not reading the RX FIFO isn't an option either * because transmission is halted once it's full. As a workaround, cyclically * clear the RX FIFO by setting the CLEAR_RX bit in the CS register. * * The CS register value is precalculated in bcm2835_spi_setup(). Normally * this is called only once, on target registration. A DMA descriptor to write * this value is preallocated in bcm2835_dma_init(). All that's left to do * when performing a TX-only transfer is to submit this descriptor to the RX * DMA channel. Latency is thereby minimized. The descriptor does not * generate any interrupts while running. It must be terminated once the * TX DMA channel is done. * * Clearing the RX FIFO is paced by the DREQ signal. The signal is asserted * when the RX FIFO becomes half full, i.e. 32 bytes. (Tuneable with the DC * register.) Reading 32 bytes from the RX FIFO would normally require 8 bus * accesses, whereas clearing it requires only 1 bus access. So an 8-fold * reduction in bus traffic and thus energy consumption is achieved. * * For *RX-only* transfers (tx_buf is %NULL), fill the TX FIFO by cyclically * copying from the zero page. The DMA descriptor to do this is preallocated * in bcm2835_dma_init(). It must be terminated once the RX DMA channel is * done and can then be reused. * * The BCM2835 DMA driver autodetects when a transaction copies from the zero * page and utilizes the DMA controller's ability to synthesize zeroes instead * of copying them from memory. This reduces traffic on the memory bus. The * feature is not available on so-called "lite" channels, but normally TX DMA * is backed by a full-featured channel. * * Zero-filling the TX FIFO is paced by the DREQ signal. Unfortunately the * BCM2835 SPI controller continues to assert DREQ even after the DLEN register * has been counted down to zero (hardware erratum). Thus, when the transfer * has finished, the DMA engine zero-fills the TX FIFO until it is half full. * (Tuneable with the DC register.) So up to 9 gratuitous bus accesses are * performed at the end of an RX-only transfer. */ static int bcm2835_spi_transfer_one_dma(struct spi_controller *ctlr, struct spi_transfer *tfr, struct bcm2835_spidev *target, u32 cs) { struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); dma_cookie_t cookie; int ret; /* update usage statistics */ bs->count_transfer_dma++; /* * Transfer first few bytes without DMA if length of first TX or RX * sglist entry is not a multiple of 4 bytes (hardware limitation). */ bcm2835_spi_transfer_prologue(ctlr, tfr, bs, cs); /* setup tx-DMA */ if (bs->tx_buf) { ret = bcm2835_spi_prepare_sg(ctlr, tfr, bs, target, true); } else { cookie = dmaengine_submit(bs->fill_tx_desc); ret = dma_submit_error(cookie); } if (ret) goto err_reset_hw; /* set the DMA length */ bcm2835_wr(bs, BCM2835_SPI_DLEN, bs->tx_len); /* start the HW */ bcm2835_wr(bs, BCM2835_SPI_CS, cs | BCM2835_SPI_CS_TA | BCM2835_SPI_CS_DMAEN); bs->tx_dma_active = true; smp_wmb(); /* start TX early */ dma_async_issue_pending(ctlr->dma_tx); /* setup rx-DMA late - to run transfers while * mapping of the rx buffers still takes place * this saves 10us or more. */ if (bs->rx_buf) { ret = bcm2835_spi_prepare_sg(ctlr, tfr, bs, target, false); } else { cookie = dmaengine_submit(target->clear_rx_desc); ret = dma_submit_error(cookie); } if (ret) { /* need to reset on errors */ dmaengine_terminate_sync(ctlr->dma_tx); bs->tx_dma_active = false; goto err_reset_hw; } /* start rx dma late */ dma_async_issue_pending(ctlr->dma_rx); bs->rx_dma_active = true; smp_mb(); /* * In case of a very short TX-only transfer, bcm2835_spi_dma_tx_done() * may run before RX DMA is issued. Terminate RX DMA if so. */ if (!bs->rx_buf && !bs->tx_dma_active && cmpxchg(&bs->rx_dma_active, true, false)) { dmaengine_terminate_async(ctlr->dma_rx); bcm2835_spi_reset_hw(bs); } /* wait for wakeup in framework */ return 1; err_reset_hw: bcm2835_spi_reset_hw(bs); bcm2835_spi_undo_prologue(bs); return ret; } static bool bcm2835_spi_can_dma(struct spi_controller *ctlr, struct spi_device *spi, struct spi_transfer *tfr) { /* we start DMA efforts only on bigger transfers */ if (tfr->len < BCM2835_SPI_DMA_MIN_LENGTH) return false; /* return OK */ return true; } static void bcm2835_dma_release(struct spi_controller *ctlr, struct bcm2835_spi *bs) { if (ctlr->dma_tx) { dmaengine_terminate_sync(ctlr->dma_tx); if (bs->fill_tx_desc) dmaengine_desc_free(bs->fill_tx_desc); if (bs->fill_tx_addr) dma_unmap_page_attrs(ctlr->dma_tx->device->dev, bs->fill_tx_addr, sizeof(u32), DMA_TO_DEVICE, DMA_ATTR_SKIP_CPU_SYNC); dma_release_channel(ctlr->dma_tx); ctlr->dma_tx = NULL; } if (ctlr->dma_rx) { dmaengine_terminate_sync(ctlr->dma_rx); dma_release_channel(ctlr->dma_rx); ctlr->dma_rx = NULL; } } static int bcm2835_dma_init(struct spi_controller *ctlr, struct device *dev, struct bcm2835_spi *bs) { struct dma_slave_config slave_config; const __be32 *addr; dma_addr_t dma_reg_base; int ret; /* base address in dma-space */ addr = of_get_address(ctlr->dev.of_node, 0, NULL, NULL); if (!addr) { dev_err(dev, "could not get DMA-register address - not using dma mode\n"); /* Fall back to interrupt mode */ return 0; } dma_reg_base = be32_to_cpup(addr); /* get tx/rx dma */ ctlr->dma_tx = dma_request_chan(dev, "tx"); if (IS_ERR(ctlr->dma_tx)) { ret = dev_err_probe(dev, PTR_ERR(ctlr->dma_tx), "no tx-dma configuration found - not using dma mode\n"); ctlr->dma_tx = NULL; goto err; } ctlr->dma_rx = dma_request_chan(dev, "rx"); if (IS_ERR(ctlr->dma_rx)) { ret = dev_err_probe(dev, PTR_ERR(ctlr->dma_rx), "no rx-dma configuration found - not using dma mode\n"); ctlr->dma_rx = NULL; goto err_release; } /* * The TX DMA channel either copies a transfer's TX buffer to the FIFO * or, in case of an RX-only transfer, cyclically copies from the zero * page to the FIFO using a preallocated, reusable descriptor. */ slave_config.dst_addr = (u32)(dma_reg_base + BCM2835_SPI_FIFO); slave_config.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES; ret = dmaengine_slave_config(ctlr->dma_tx, &slave_config); if (ret) goto err_config; bs->fill_tx_addr = dma_map_page_attrs(ctlr->dma_tx->device->dev, ZERO_PAGE(0), 0, sizeof(u32), DMA_TO_DEVICE, DMA_ATTR_SKIP_CPU_SYNC); if (dma_mapping_error(ctlr->dma_tx->device->dev, bs->fill_tx_addr)) { dev_err(dev, "cannot map zero page - not using DMA mode\n"); bs->fill_tx_addr = 0; ret = -ENOMEM; goto err_release; } bs->fill_tx_desc = dmaengine_prep_dma_cyclic(ctlr->dma_tx, bs->fill_tx_addr, sizeof(u32), 0, DMA_MEM_TO_DEV, 0); if (!bs->fill_tx_desc) { dev_err(dev, "cannot prepare fill_tx_desc - not using DMA mode\n"); ret = -ENOMEM; goto err_release; } ret = dmaengine_desc_set_reuse(bs->fill_tx_desc); if (ret) { dev_err(dev, "cannot reuse fill_tx_desc - not using DMA mode\n"); goto err_release; } /* * The RX DMA channel is used bidirectionally: It either reads the * RX FIFO or, in case of a TX-only transfer, cyclically writes a * precalculated value to the CS register to clear the RX FIFO. */ slave_config.src_addr = (u32)(dma_reg_base + BCM2835_SPI_FIFO); slave_config.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES; slave_config.dst_addr = (u32)(dma_reg_base + BCM2835_SPI_CS); slave_config.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES; ret = dmaengine_slave_config(ctlr->dma_rx, &slave_config); if (ret) goto err_config; /* all went well, so set can_dma */ ctlr->can_dma = bcm2835_spi_can_dma; return 0; err_config: dev_err(dev, "issue configuring dma: %d - not using DMA mode\n", ret); err_release: bcm2835_dma_release(ctlr, bs); err: /* * Only report error for deferred probing, otherwise fall back to * interrupt mode */ if (ret != -EPROBE_DEFER) ret = 0; return ret; } static int bcm2835_spi_transfer_one_poll(struct spi_controller *ctlr, struct spi_device *spi, struct spi_transfer *tfr, u32 cs) { struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); unsigned long timeout; /* update usage statistics */ bs->count_transfer_polling++; /* enable HW block without interrupts */ bcm2835_wr(bs, BCM2835_SPI_CS, cs | BCM2835_SPI_CS_TA); /* fill in the fifo before timeout calculations * if we are interrupted here, then the data is * getting transferred by the HW while we are interrupted */ bcm2835_wr_fifo_blind(bs, BCM2835_SPI_FIFO_SIZE); /* set the timeout to at least 2 jiffies */ timeout = jiffies + 2 + HZ * polling_limit_us / 1000000; /* loop until finished the transfer */ while (bs->rx_len) { /* fill in tx fifo with remaining data */ bcm2835_wr_fifo(bs); /* read from fifo as much as possible */ bcm2835_rd_fifo(bs); /* if there is still data pending to read * then check the timeout */ if (bs->rx_len && time_after(jiffies, timeout)) { dev_dbg_ratelimited(&spi->dev, "timeout period reached: jiffies: %lu remaining tx/rx: %d/%d - falling back to interrupt mode\n", jiffies - timeout, bs->tx_len, bs->rx_len); /* fall back to interrupt mode */ /* update usage statistics */ bs->count_transfer_irq_after_polling++; return bcm2835_spi_transfer_one_irq(ctlr, spi, tfr, cs, false); } } /* Transfer complete - reset SPI HW */ bcm2835_spi_reset_hw(bs); /* and return without waiting for completion */ return 0; } static int bcm2835_spi_transfer_one(struct spi_controller *ctlr, struct spi_device *spi, struct spi_transfer *tfr) { struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); struct bcm2835_spidev *target = spi_get_ctldata(spi); unsigned long spi_hz, cdiv; unsigned long hz_per_byte, byte_limit; u32 cs = target->prepare_cs; /* set clock */ spi_hz = tfr->speed_hz; if (spi_hz >= bs->clk_hz / 2) { cdiv = 2; /* clk_hz/2 is the fastest we can go */ } else if (spi_hz) { /* CDIV must be a multiple of two */ cdiv = DIV_ROUND_UP(bs->clk_hz, spi_hz); cdiv += (cdiv % 2); if (cdiv >= 65536) cdiv = 0; /* 0 is the slowest we can go */ } else { cdiv = 0; /* 0 is the slowest we can go */ } tfr->effective_speed_hz = cdiv ? (bs->clk_hz / cdiv) : (bs->clk_hz / 65536); bcm2835_wr(bs, BCM2835_SPI_CLK, cdiv); /* handle all the 3-wire mode */ if (spi->mode & SPI_3WIRE && tfr->rx_buf) cs |= BCM2835_SPI_CS_REN; /* set transmit buffers and length */ bs->tx_buf = tfr->tx_buf; bs->rx_buf = tfr->rx_buf; bs->tx_len = tfr->len; bs->rx_len = tfr->len; /* Calculate the estimated time in us the transfer runs. Note that * there is 1 idle clocks cycles after each byte getting transferred * so we have 9 cycles/byte. This is used to find the number of Hz * per byte per polling limit. E.g., we can transfer 1 byte in 30 us * per 300,000 Hz of bus clock. */ hz_per_byte = polling_limit_us ? (9 * 1000000) / polling_limit_us : 0; byte_limit = hz_per_byte ? tfr->effective_speed_hz / hz_per_byte : 1; /* run in polling mode for short transfers */ if (tfr->len < byte_limit) return bcm2835_spi_transfer_one_poll(ctlr, spi, tfr, cs); /* run in dma mode if conditions are right * Note that unlike poll or interrupt mode DMA mode does not have * this 1 idle clock cycle pattern but runs the spi clock without gaps */ if (ctlr->can_dma && bcm2835_spi_can_dma(ctlr, spi, tfr)) return bcm2835_spi_transfer_one_dma(ctlr, tfr, target, cs); /* run in interrupt-mode */ return bcm2835_spi_transfer_one_irq(ctlr, spi, tfr, cs, true); } static int bcm2835_spi_prepare_message(struct spi_controller *ctlr, struct spi_message *msg) { struct spi_device *spi = msg->spi; struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); struct bcm2835_spidev *target = spi_get_ctldata(spi); /* * Set up clock polarity before spi_transfer_one_message() asserts * chip select to avoid a gratuitous clock signal edge. */ bcm2835_wr(bs, BCM2835_SPI_CS, target->prepare_cs); return 0; } static void bcm2835_spi_handle_err(struct spi_controller *ctlr, struct spi_message *msg) { struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); /* if an error occurred and we have an active dma, then terminate */ if (ctlr->dma_tx) { dmaengine_terminate_sync(ctlr->dma_tx); bs->tx_dma_active = false; } if (ctlr->dma_rx) { dmaengine_terminate_sync(ctlr->dma_rx); bs->rx_dma_active = false; } bcm2835_spi_undo_prologue(bs); /* and reset */ bcm2835_spi_reset_hw(bs); } static void bcm2835_spi_cleanup(struct spi_device *spi) { struct bcm2835_spidev *target = spi_get_ctldata(spi); struct spi_controller *ctlr = spi->controller; struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); if (target->clear_rx_desc) dmaengine_desc_free(target->clear_rx_desc); if (target->clear_rx_addr) dma_unmap_single(ctlr->dma_rx->device->dev, target->clear_rx_addr, sizeof(u32), DMA_TO_DEVICE); gpiod_put(bs->cs_gpio); spi_set_csgpiod(spi, 0, NULL); kfree(target); } static int bcm2835_spi_setup_dma(struct spi_controller *ctlr, struct spi_device *spi, struct bcm2835_spi *bs, struct bcm2835_spidev *target) { int ret; if (!ctlr->dma_rx) return 0; target->clear_rx_addr = dma_map_single(ctlr->dma_rx->device->dev, &target->clear_rx_cs, sizeof(u32), DMA_TO_DEVICE); if (dma_mapping_error(ctlr->dma_rx->device->dev, target->clear_rx_addr)) { dev_err(&spi->dev, "cannot map clear_rx_cs\n"); target->clear_rx_addr = 0; return -ENOMEM; } target->clear_rx_desc = dmaengine_prep_dma_cyclic(ctlr->dma_rx, target->clear_rx_addr, sizeof(u32), 0, DMA_MEM_TO_DEV, 0); if (!target->clear_rx_desc) { dev_err(&spi->dev, "cannot prepare clear_rx_desc\n"); return -ENOMEM; } ret = dmaengine_desc_set_reuse(target->clear_rx_desc); if (ret) { dev_err(&spi->dev, "cannot reuse clear_rx_desc\n"); return ret; } return 0; } static size_t bcm2835_spi_max_transfer_size(struct spi_device *spi) { /* * DMA transfers are limited to 16 bit (0 to 65535 bytes) by * the SPI HW due to DLEN. Split up transfers (32-bit FIFO * aligned) if the limit is exceeded. */ if (spi->controller->can_dma) return 65532; return SIZE_MAX; } static int bcm2835_spi_setup(struct spi_device *spi) { struct spi_controller *ctlr = spi->controller; struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); struct bcm2835_spidev *target = spi_get_ctldata(spi); struct gpiod_lookup_table *lookup __free(kfree) = NULL; int ret; u32 cs; if (!target) { target = kzalloc(ALIGN(sizeof(*target), dma_get_cache_alignment()), GFP_KERNEL); if (!target) return -ENOMEM; spi_set_ctldata(spi, target); ret = bcm2835_spi_setup_dma(ctlr, spi, bs, target); if (ret) goto err_cleanup; } /* * Precalculate SPI target's CS register value for ->prepare_message(): * The driver always uses software-controlled GPIO chip select, hence * set the hardware-controlled native chip select to an invalid value * to prevent it from interfering. */ cs = BCM2835_SPI_CS_CS_10 | BCM2835_SPI_CS_CS_01; if (spi->mode & SPI_CPOL) cs |= BCM2835_SPI_CS_CPOL; if (spi->mode & SPI_CPHA) cs |= BCM2835_SPI_CS_CPHA; target->prepare_cs = cs; /* * Precalculate SPI target's CS register value to clear RX FIFO * in case of a TX-only DMA transfer. */ if (ctlr->dma_rx) { target->clear_rx_cs = cs | BCM2835_SPI_CS_TA | BCM2835_SPI_CS_DMAEN | BCM2835_SPI_CS_CLEAR_RX; dma_sync_single_for_device(ctlr->dma_rx->device->dev, target->clear_rx_addr, sizeof(u32), DMA_TO_DEVICE); } /* * sanity checking the native-chipselects */ if (spi->mode & SPI_NO_CS) return 0; /* * The SPI core has successfully requested the CS GPIO line from the * device tree, so we are done. */ if (spi_get_csgpiod(spi, 0)) return 0; if (spi_get_chipselect(spi, 0) > 1) { /* error in the case of native CS requested with CS > 1 * officially there is a CS2, but it is not documented * which GPIO is connected with that... */ dev_err(&spi->dev, "setup: only two native chip-selects are supported\n"); ret = -EINVAL; goto err_cleanup; } /* * TODO: The code below is a slightly better alternative to the utter * abuse of the GPIO API that I found here before. It creates a * temporary lookup table, assigns it to the SPI device, gets the GPIO * descriptor and then releases the lookup table. * * More on the problem that it addresses: * https://www.spinics.net/lists/linux-gpio/msg36218.html */ lookup = kzalloc(struct_size(lookup, table, 2), GFP_KERNEL); if (!lookup) { ret = -ENOMEM; goto err_cleanup; } lookup->dev_id = dev_name(&spi->dev); lookup->table[0] = GPIO_LOOKUP("pinctrl-bcm2835", 8 - (spi_get_chipselect(spi, 0)), "cs", GPIO_LOOKUP_FLAGS_DEFAULT); gpiod_add_lookup_table(lookup); bs->cs_gpio = gpiod_get(&spi->dev, "cs", GPIOD_OUT_LOW); gpiod_remove_lookup_table(lookup); if (IS_ERR(bs->cs_gpio)) { ret = PTR_ERR(bs->cs_gpio); goto err_cleanup; } spi_set_csgpiod(spi, 0, bs->cs_gpio); /* and set up the "mode" and level */ dev_info(&spi->dev, "setting up native-CS%i to use GPIO\n", spi_get_chipselect(spi, 0)); return 0; err_cleanup: bcm2835_spi_cleanup(spi); return ret; } static int bcm2835_spi_probe(struct platform_device *pdev) { struct spi_controller *ctlr; struct bcm2835_spi *bs; int err; ctlr = devm_spi_alloc_host(&pdev->dev, sizeof(*bs)); if (!ctlr) return -ENOMEM; platform_set_drvdata(pdev, ctlr); ctlr->use_gpio_descriptors = true; ctlr->mode_bits = BCM2835_SPI_MODE_BITS; ctlr->bits_per_word_mask = SPI_BPW_MASK(8); ctlr->num_chipselect = 3; ctlr->max_transfer_size = bcm2835_spi_max_transfer_size; ctlr->setup = bcm2835_spi_setup; ctlr->cleanup = bcm2835_spi_cleanup; ctlr->transfer_one = bcm2835_spi_transfer_one; ctlr->handle_err = bcm2835_spi_handle_err; ctlr->prepare_message = bcm2835_spi_prepare_message; ctlr->dev.of_node = pdev->dev.of_node; bs = spi_controller_get_devdata(ctlr); bs->ctlr = ctlr; bs->regs = devm_platform_ioremap_resource(pdev, 0); if (IS_ERR(bs->regs)) return PTR_ERR(bs->regs); bs->clk = devm_clk_get_enabled(&pdev->dev, NULL); if (IS_ERR(bs->clk)) return dev_err_probe(&pdev->dev, PTR_ERR(bs->clk), "could not get clk\n"); ctlr->max_speed_hz = clk_get_rate(bs->clk) / 2; bs->irq = platform_get_irq(pdev, 0); if (bs->irq < 0) return bs->irq; bs->clk_hz = clk_get_rate(bs->clk); err = bcm2835_dma_init(ctlr, &pdev->dev, bs); if (err) return err; /* initialise the hardware with the default polarities */ bcm2835_wr(bs, BCM2835_SPI_CS, BCM2835_SPI_CS_CLEAR_RX | BCM2835_SPI_CS_CLEAR_TX); err = devm_request_irq(&pdev->dev, bs->irq, bcm2835_spi_interrupt, IRQF_SHARED, dev_name(&pdev->dev), bs); if (err) { dev_err(&pdev->dev, "could not request IRQ: %d\n", err); goto out_dma_release; } err = spi_register_controller(ctlr); if (err) { dev_err(&pdev->dev, "could not register SPI controller: %d\n", err); goto out_dma_release; } bcm2835_debugfs_create(bs, dev_name(&pdev->dev)); return 0; out_dma_release: bcm2835_dma_release(ctlr, bs); return err; } static void bcm2835_spi_remove(struct platform_device *pdev) { struct spi_controller *ctlr = platform_get_drvdata(pdev); struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); bcm2835_debugfs_remove(bs); spi_unregister_controller(ctlr); bcm2835_dma_release(ctlr, bs); /* Clear FIFOs, and disable the HW block */ bcm2835_wr(bs, BCM2835_SPI_CS, BCM2835_SPI_CS_CLEAR_RX | BCM2835_SPI_CS_CLEAR_TX); } static const struct of_device_id bcm2835_spi_match[] = { { .compatible = "brcm,bcm2835-spi", }, {} }; MODULE_DEVICE_TABLE(of, bcm2835_spi_match); static struct platform_driver bcm2835_spi_driver = { .driver = { .name = DRV_NAME, .of_match_table = bcm2835_spi_match, }, .probe = bcm2835_spi_probe, .remove = bcm2835_spi_remove, .shutdown = bcm2835_spi_remove, }; module_platform_driver(bcm2835_spi_driver); MODULE_DESCRIPTION("SPI controller driver for Broadcom BCM2835"); MODULE_AUTHOR("Chris Boot "); MODULE_LICENSE("GPL");