diff options
Diffstat (limited to 'drivers/spi')
| -rw-r--r-- | drivers/spi/spi-bcm2835.c | 112 |
1 files changed, 86 insertions, 26 deletions
diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c index 90064494e828..f63864a893c5 100644 --- a/drivers/spi/spi-bcm2835.c +++ b/drivers/spi/spi-bcm2835.c @@ -68,7 +68,8 @@ #define BCM2835_SPI_CS_CS_10 0x00000002 #define BCM2835_SPI_CS_CS_01 0x00000001 -#define BCM2835_SPI_TIMEOUT_MS 30000 +#define BCM2835_SPI_POLLING_LIMIT_US 30 +#define BCM2835_SPI_TIMEOUT_MS 30000 #define BCM2835_SPI_MODE_BITS (SPI_CPOL | SPI_CPHA | SPI_CS_HIGH \ | SPI_NO_CS | SPI_3WIRE) @@ -156,12 +157,86 @@ static irqreturn_t bcm2835_spi_interrupt(int irq, void *dev_id) return IRQ_HANDLED; } +static int bcm2835_spi_transfer_one_poll(struct spi_master *master, + struct spi_device *spi, + struct spi_transfer *tfr, + u32 cs, + unsigned long xfer_time_us) +{ + struct bcm2835_spi *bs = spi_master_get_devdata(master); + unsigned long timeout = jiffies + + max(4 * xfer_time_us * HZ / 1000000, 2uL); + + /* enable HW block without interrupts */ + bcm2835_wr(bs, BCM2835_SPI_CS, cs | BCM2835_SPI_CS_TA); + + /* set timeout to 4x the expected time, or 2 jiffies */ + /* loop until finished the transfer */ + while (bs->rx_len) { + /* read from fifo as much as possible */ + bcm2835_rd_fifo(bs); + /* fill in tx fifo as much as possible */ + bcm2835_wr_fifo(bs); + /* if we still expect some data after the read, + * check for a possible timeout + */ + if (bs->rx_len && time_after(jiffies, timeout)) { + /* Transfer complete - reset SPI HW */ + bcm2835_spi_reset_hw(master); + /* and return timeout */ + return -ETIMEDOUT; + } + } + + /* Transfer complete - reset SPI HW */ + bcm2835_spi_reset_hw(master); + /* and return without waiting for completion */ + return 0; +} + +static int bcm2835_spi_transfer_one_irq(struct spi_master *master, + struct spi_device *spi, + struct spi_transfer *tfr, + u32 cs) +{ + struct bcm2835_spi *bs = spi_master_get_devdata(master); + + /* fill in fifo if we have gpio-cs + * note that there have been rare events where the native-CS + * flapped for <1us which may change the behaviour + * with gpio-cs this does not happen, so it is implemented + * only for this case + */ + if (gpio_is_valid(spi->cs_gpio)) { + /* enable HW block, but without interrupts enabled + * this would triggern an immediate interrupt + */ + bcm2835_wr(bs, BCM2835_SPI_CS, + cs | BCM2835_SPI_CS_TA); + /* fill in tx fifo as much as possible */ + bcm2835_wr_fifo(bs); + } + + /* + * Enable the HW block. This will immediately trigger a DONE (TX + * empty) interrupt, upon which we will fill the TX FIFO with the + * first TX bytes. Pre-filling the TX FIFO here to avoid the + * interrupt doesn't work:-( + */ + 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; +} + static int bcm2835_spi_transfer_one(struct spi_master *master, struct spi_device *spi, struct spi_transfer *tfr) { struct bcm2835_spi *bs = spi_master_get_devdata(master); unsigned long spi_hz, clk_hz, cdiv; + unsigned long spi_used_hz, xfer_time_us; u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS); /* set clock */ @@ -180,6 +255,7 @@ static int bcm2835_spi_transfer_one(struct spi_master *master, } else { cdiv = 0; /* 0 is the slowest we can go */ } + spi_used_hz = cdiv ? (clk_hz / cdiv) : (clk_hz / 65536); bcm2835_wr(bs, BCM2835_SPI_CLK, cdiv); /* handle all the modes */ @@ -203,33 +279,17 @@ static int bcm2835_spi_transfer_one(struct spi_master *master, bs->tx_len = tfr->len; bs->rx_len = tfr->len; - /* fill in fifo if we have gpio-cs - * note that there have been rare events where the native-CS - * flapped for <1us which may change the behaviour - * with gpio-cs this does not happen, so it is implemented - * only for this case - */ - if (gpio_is_valid(spi->cs_gpio)) { - /* enable HW block, but without interrupts enabled - * this would triggern an immediate interrupt - */ - bcm2835_wr(bs, BCM2835_SPI_CS, - cs | BCM2835_SPI_CS_TA); - /* fill in tx fifo as much as possible */ - bcm2835_wr_fifo(bs); - } + /* calculate the estimated time in us the transfer runs */ + xfer_time_us = tfr->len + * 9 /* clocks/byte - SPI-HW waits 1 clock after each byte */ + * 1000000 / spi_used_hz; - /* - * Enable the HW block. This will immediately trigger a DONE (TX - * empty) interrupt, upon which we will fill the TX FIFO with the - * first TX bytes. Pre-filling the TX FIFO here to avoid the - * interrupt doesn't work:-( - */ - cs |= BCM2835_SPI_CS_INTR | BCM2835_SPI_CS_INTD | BCM2835_SPI_CS_TA; - bcm2835_wr(bs, BCM2835_SPI_CS, cs); + /* for short requests run polling*/ + if (xfer_time_us <= BCM2835_SPI_POLLING_LIMIT_US) + return bcm2835_spi_transfer_one_poll(master, spi, tfr, + cs, xfer_time_us); - /* signal that we need to wait for completion */ - return 1; + return bcm2835_spi_transfer_one_irq(master, spi, tfr, cs); } static void bcm2835_spi_handle_err(struct spi_master *master, |