diff options
| -rw-r--r-- | drivers/spi/spi-bcm2835.c | 241 |
1 files changed, 218 insertions, 23 deletions
diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c index f01d18d521f2..3fe823891861 100644 --- a/drivers/spi/spi-bcm2835.c +++ b/drivers/spi/spi-bcm2835.c @@ -106,6 +106,16 @@ MODULE_PARM_DESC(polling_limit_us, * These are counted as well in @count_transfer_polling and * @count_transfer_irq * @count_transfer_dma: count how often dma mode is used + * @chip_select: SPI slave 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) + * @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 slave-specific clock polarity and phase settings) */ struct bcm2835_spi { void __iomem *regs; @@ -126,6 +136,13 @@ struct bcm2835_spi { u64 count_transfer_irq; u64 count_transfer_irq_after_polling; u64 count_transfer_dma; + + u8 chip_select; + unsigned int tx_dma_active; + unsigned int rx_dma_active; + struct dma_async_tx_descriptor *clear_rx_desc[BCM2835_SPI_NUM_CS]; + dma_addr_t clear_rx_addr; + u32 clear_rx_cs[BCM2835_SPI_NUM_CS] ____cacheline_aligned; }; #if defined(CONFIG_DEBUG_FS) @@ -455,7 +472,7 @@ static void bcm2835_spi_transfer_prologue(struct spi_controller *ctlr, if (!sg_is_last(&tfr->tx_sg.sgl[0])) bs->tx_prologue = sg_dma_len(&tfr->tx_sg.sgl[0]) & 3; - if (!sg_is_last(&tfr->rx_sg.sgl[0])) { + 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) { @@ -547,7 +564,13 @@ static void bcm2835_spi_undo_prologue(struct bcm2835_spi *bs) bs->tx_prologue = 0; } -static void bcm2835_spi_dma_done(void *data) +/** + * bcm2835_spi_dma_rx_done() - callback for DMA RX channel + * @data: SPI master 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); @@ -561,14 +584,61 @@ static void bcm2835_spi_dma_done(void *data) * situation otherwise... */ dmaengine_terminate_async(ctlr->dma_tx); + bs->tx_dma_active = false; + bs->rx_dma_active = false; bcm2835_spi_undo_prologue(bs); /* and mark as completed */; complete(&ctlr->xfer_completion); } +/** + * bcm2835_spi_dma_tx_done() - callback for DMA TX channel + * @data: SPI master 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->clear_rx_cs[bs->chip_select]); + + 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(ctlr); + complete(&ctlr->xfer_completion); +} + +/** + * bcm2835_spi_prepare_sg() - prepare and submit DMA descriptor for sglist + * @ctlr: SPI master controller + * @spi: SPI slave + * @tfr: SPI transfer + * @bs: BCM2835 SPI controller + * @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_device *spi, struct spi_transfer *tfr, + struct bcm2835_spi *bs, bool is_tx) { struct dma_chan *chan; @@ -585,8 +655,7 @@ static int bcm2835_spi_prepare_sg(struct spi_controller *ctlr, chan = ctlr->dma_tx; nents = tfr->tx_sg.nents; sgl = tfr->tx_sg.sgl; - flags = 0 /* no tx interrupt */; - + flags = tfr->rx_buf ? 0 : DMA_PREP_INTERRUPT; } else { dir = DMA_DEV_TO_MEM; chan = ctlr->dma_rx; @@ -599,10 +668,17 @@ static int bcm2835_spi_prepare_sg(struct spi_controller *ctlr, if (!desc) return -EINVAL; - /* set callback for rx */ + /* + * 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_done; + 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->chip_select = spi->chip_select; } /* submit it to DMA-engine */ @@ -611,12 +687,42 @@ static int bcm2835_spi_prepare_sg(struct spi_controller *ctlr, return dma_submit_error(cookie); } +/** + * bcm2835_spi_transfer_one_dma() - perform SPI transfer using DMA engine + * @ctlr: SPI master controller + * @spi: SPI slave + * @tfr: SPI transfer + * @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 slave 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. + */ static int bcm2835_spi_transfer_one_dma(struct spi_controller *ctlr, struct spi_device *spi, struct spi_transfer *tfr, u32 cs) { struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); + dma_cookie_t cookie; int ret; /* update usage statistics */ @@ -629,13 +735,10 @@ static int bcm2835_spi_transfer_one_dma(struct spi_controller *ctlr, bcm2835_spi_transfer_prologue(ctlr, tfr, bs, cs); /* setup tx-DMA */ - ret = bcm2835_spi_prepare_sg(ctlr, tfr, true); + ret = bcm2835_spi_prepare_sg(ctlr, spi, tfr, bs, true); if (ret) goto err_reset_hw; - /* start TX early */ - dma_async_issue_pending(ctlr->dma_tx); - /* set the DMA length */ bcm2835_wr(bs, BCM2835_SPI_DLEN, bs->tx_len); @@ -643,19 +746,43 @@ static int bcm2835_spi_transfer_one_dma(struct spi_controller *ctlr, 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. */ - ret = bcm2835_spi_prepare_sg(ctlr, tfr, false); + if (bs->rx_buf) { + ret = bcm2835_spi_prepare_sg(ctlr, spi, tfr, bs, false); + } else { + cookie = dmaengine_submit(bs->clear_rx_desc[spi->chip_select]); + 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(ctlr); + } /* wait for wakeup in framework */ return 1; @@ -678,26 +805,42 @@ static bool bcm2835_spi_can_dma(struct spi_controller *ctlr, return true; } -static void bcm2835_dma_release(struct spi_controller *ctlr) +static void bcm2835_dma_release(struct spi_controller *ctlr, + struct bcm2835_spi *bs) { + int i; + if (ctlr->dma_tx) { dmaengine_terminate_sync(ctlr->dma_tx); dma_release_channel(ctlr->dma_tx); ctlr->dma_tx = NULL; } + if (ctlr->dma_rx) { dmaengine_terminate_sync(ctlr->dma_rx); + + for (i = 0; i < BCM2835_SPI_NUM_CS; i++) + if (bs->clear_rx_desc[i]) + dmaengine_desc_free(bs->clear_rx_desc[i]); + + if (bs->clear_rx_addr) + dma_unmap_single(ctlr->dma_rx->device->dev, + bs->clear_rx_addr, + sizeof(bs->clear_rx_cs), + DMA_TO_DEVICE); + dma_release_channel(ctlr->dma_rx); ctlr->dma_rx = NULL; } } -static void bcm2835_dma_init(struct spi_controller *ctlr, struct device *dev) +static void 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; + int ret, i; /* base address in dma-space */ addr = of_get_address(ctlr->dev.of_node, 0, NULL, NULL); @@ -727,17 +870,51 @@ static void bcm2835_dma_init(struct spi_controller *ctlr, struct device *dev) if (ret) goto err_config; + /* + * 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; + bs->clear_rx_addr = dma_map_single(ctlr->dma_rx->device->dev, + bs->clear_rx_cs, + sizeof(bs->clear_rx_cs), + DMA_TO_DEVICE); + if (dma_mapping_error(ctlr->dma_rx->device->dev, bs->clear_rx_addr)) { + dev_err(dev, "cannot map clear_rx_cs - not using DMA mode\n"); + bs->clear_rx_addr = 0; + goto err_release; + } + + for (i = 0; i < BCM2835_SPI_NUM_CS; i++) { + bs->clear_rx_desc[i] = dmaengine_prep_dma_cyclic(ctlr->dma_rx, + bs->clear_rx_addr + i * sizeof(u32), + sizeof(u32), 0, + DMA_MEM_TO_DEV, 0); + if (!bs->clear_rx_desc[i]) { + dev_err(dev, "cannot prepare clear_rx_desc - not using DMA mode\n"); + goto err_release; + } + + ret = dmaengine_desc_set_reuse(bs->clear_rx_desc[i]); + if (ret) { + dev_err(dev, "cannot reuse clear_rx_desc - not using DMA mode\n"); + goto err_release; + } + } + /* all went well, so set can_dma */ ctlr->can_dma = bcm2835_spi_can_dma; - /* need to do TX AND RX DMA, so we need dummy buffers */ - ctlr->flags = SPI_CONTROLLER_MUST_RX | SPI_CONTROLLER_MUST_TX; + /* need to do TX DMA, so we need a dummy buffer */ + ctlr->flags = SPI_CONTROLLER_MUST_TX; return; @@ -745,7 +922,7 @@ err_config: dev_err(dev, "issue configuring dma: %d - not using DMA mode\n", ret); err_release: - bcm2835_dma_release(ctlr); + bcm2835_dma_release(ctlr, bs); err: return; } @@ -834,8 +1011,7 @@ static int bcm2835_spi_transfer_one(struct spi_controller *ctlr, bcm2835_wr(bs, BCM2835_SPI_CLK, cdiv); /* handle all the 3-wire mode */ - if (spi->mode & SPI_3WIRE && tfr->rx_buf && - tfr->rx_buf != ctlr->dummy_rx) + if (spi->mode & SPI_3WIRE && tfr->rx_buf) cs |= BCM2835_SPI_CS_REN; /* set transmit buffers and length */ @@ -903,7 +1079,9 @@ static void bcm2835_spi_handle_err(struct spi_controller *ctlr, /* if an error occurred and we have an active dma, then terminate */ dmaengine_terminate_sync(ctlr->dma_tx); + bs->tx_dma_active = false; dmaengine_terminate_sync(ctlr->dma_rx); + bs->rx_dma_active = false; bcm2835_spi_undo_prologue(bs); /* and reset */ @@ -917,7 +1095,8 @@ static int chip_match_name(struct gpio_chip *chip, void *data) static int bcm2835_spi_setup(struct spi_device *spi) { - struct bcm2835_spi *bs = spi_controller_get_devdata(spi->controller); + struct spi_controller *ctlr = spi->controller; + struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr); struct gpio_chip *chip; enum gpio_lookup_flags lflags; u32 cs; @@ -936,6 +1115,21 @@ static int bcm2835_spi_setup(struct spi_device *spi) bs->prepare_cs[spi->chip_select] = cs; /* + * Precalculate SPI slave's CS register value to clear RX FIFO + * in case of a TX-only DMA transfer. + */ + if (ctlr->dma_rx) { + bs->clear_rx_cs[spi->chip_select] = cs | + BCM2835_SPI_CS_TA | + BCM2835_SPI_CS_DMAEN | + BCM2835_SPI_CS_CLEAR_RX; + dma_sync_single_for_device(ctlr->dma_rx->device->dev, + bs->clear_rx_addr, + sizeof(bs->clear_rx_cs), + DMA_TO_DEVICE); + } + + /* * sanity checking the native-chipselects */ if (spi->mode & SPI_NO_CS) @@ -1002,7 +1196,8 @@ static int bcm2835_spi_probe(struct platform_device *pdev) struct bcm2835_spi *bs; int err; - ctlr = spi_alloc_master(&pdev->dev, sizeof(*bs)); + ctlr = spi_alloc_master(&pdev->dev, ALIGN(sizeof(*bs), + dma_get_cache_alignment())); if (!ctlr) return -ENOMEM; @@ -1041,7 +1236,7 @@ static int bcm2835_spi_probe(struct platform_device *pdev) clk_prepare_enable(bs->clk); - bcm2835_dma_init(ctlr, &pdev->dev); + bcm2835_dma_init(ctlr, &pdev->dev, bs); /* initialise the hardware with the default polarities */ bcm2835_wr(bs, BCM2835_SPI_CS, @@ -1085,7 +1280,7 @@ static int bcm2835_spi_remove(struct platform_device *pdev) clk_disable_unprepare(bs->clk); - bcm2835_dma_release(ctlr); + bcm2835_dma_release(ctlr, bs); return 0; } |