From 4adf312976ef2b72830b83f212fef3f6a36513a6 Mon Sep 17 00:00:00 2001 From: Martin Sperl Date: Mon, 23 Mar 2015 15:11:53 +0100 Subject: [PATCH] spi: bcm2835: fill/drain SPI-fifo as much as possible during interrupt Implement the recommendation from the BCM2835 data-sheet with regards to polling drivers to fill/drain the FIFO as much data as possible also for the interrupt-driven case (which this driver is making use of). This means that for long transfers (>64bytes) we need one interrupt every 64 bytes instead of every 12 bytes, as the FIFO is 16 words (not bytes) wide. Tested with mcp251x (can bus), fb_st7735 (TFT framebuffer device) and enc28j60 (ethernet) drivers. Signed-off-by: Martin Sperl Signed-off-by: Mark Brown --- drivers/spi/spi-bcm2835.c | 78 +++++++++------------------------------ 1 file changed, 17 insertions(+), 61 deletions(-) diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c index 779d3a86c3cb..960dcce607c2 100644 --- a/drivers/spi/spi-bcm2835.c +++ b/drivers/spi/spi-bcm2835.c @@ -91,25 +91,23 @@ static inline void bcm2835_wr(struct bcm2835_spi *bs, unsigned reg, u32 val) writel(val, bs->regs + reg); } -static inline void bcm2835_rd_fifo(struct bcm2835_spi *bs, int len) +static inline void bcm2835_rd_fifo(struct bcm2835_spi *bs) { u8 byte; - while (len--) { + while (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; } } -static inline void bcm2835_wr_fifo(struct bcm2835_spi *bs, int len) +static inline void bcm2835_wr_fifo(struct bcm2835_spi *bs) { u8 byte; - if (len > bs->len) - len = bs->len; - - while (len--) { + while ((bs->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->len--; @@ -122,60 +120,24 @@ static irqreturn_t bcm2835_spi_interrupt(int irq, void *dev_id) struct bcm2835_spi *bs = spi_master_get_devdata(master); u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS); - /* - * RXR - RX needs Reading. This means 12 (or more) bytes have been - * transmitted and hence 12 (or more) bytes have been received. - * - * The FIFO is 16-bytes deep. We check for this interrupt to keep the - * FIFO full; we have a 4-byte-time buffer for IRQ latency. We check - * this before DONE (TX empty) just in case we delayed processing this - * interrupt for some reason. - * - * We only check for this case if we have more bytes to TX; at the end - * of the transfer, we ignore this pipelining optimization, and let - * bcm2835_spi_finish_transfer() drain the RX FIFO. - */ - if (bs->len && (cs & BCM2835_SPI_CS_RXR)) { - /* Read 12 bytes of data */ - bcm2835_rd_fifo(bs, 12); + /* Read as many bytes as possible from FIFO */ + bcm2835_rd_fifo(bs); - /* Write up to 12 bytes */ - bcm2835_wr_fifo(bs, 12); + if (bs->len) { /* there is more data to transmit */ + bcm2835_wr_fifo(bs); + } else { /* Transfer complete */ + /* Disable SPI interrupts */ + cs &= ~(BCM2835_SPI_CS_INTR | BCM2835_SPI_CS_INTD); + bcm2835_wr(bs, BCM2835_SPI_CS, cs); /* - * We must have written something to the TX FIFO due to the - * bs->len check above, so cannot be DONE. Hence, return - * early. Note that DONE could also be set if we serviced an - * RXR interrupt really late. + * Wake up bcm2835_spi_transfer_one(), which will call + * bcm2835_spi_finish_transfer(), to drain the RX FIFO. */ - return IRQ_HANDLED; + complete(&bs->done); } - /* - * DONE - TX empty. This occurs when we first enable the transfer - * since we do not pre-fill the TX FIFO. At any other time, given that - * we refill the TX FIFO above based on RXR, and hence ignore DONE if - * RXR is set, DONE really does mean end-of-transfer. - */ - if (cs & BCM2835_SPI_CS_DONE) { - if (bs->len) { /* First interrupt in a transfer */ - bcm2835_wr_fifo(bs, 16); - } else { /* Transfer complete */ - /* Disable SPI interrupts */ - cs &= ~(BCM2835_SPI_CS_INTR | BCM2835_SPI_CS_INTD); - bcm2835_wr(bs, BCM2835_SPI_CS, cs); - - /* - * Wake up bcm2835_spi_transfer_one(), which will call - * bcm2835_spi_finish_transfer(), to drain the RX FIFO. - */ - complete(&bs->done); - } - - return IRQ_HANDLED; - } - - return IRQ_NONE; + return IRQ_HANDLED; } static int bcm2835_spi_start_transfer(struct spi_device *spi, @@ -238,12 +200,6 @@ static int bcm2835_spi_finish_transfer(struct spi_device *spi, struct bcm2835_spi *bs = spi_master_get_devdata(spi->master); u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS); - /* Drain RX FIFO */ - while (cs & BCM2835_SPI_CS_RXD) { - bcm2835_rd_fifo(bs, 1); - cs = bcm2835_rd(bs, BCM2835_SPI_CS); - } - if (tfr->delay_usecs) udelay(tfr->delay_usecs); -- 2.20.1