From 7f1922eb3adba8c372fdf0d04fe9e6268f98291a Mon Sep 17 00:00:00 2001 From: Martin Sperl Date: Tue, 23 Apr 2019 20:15:09 +0000 Subject: spi: bcm2835: Avoid 64-bit arithmetic in xfer len calc Avoid 64 bit aritmetics when deciding if we need to use polling or not This replicates: commit d704afffe65c ("spi: bcm2835aux: Avoid 64-bit arithmetic in xfer len calc") from spi-bcm2835aux Signed-off-by: Martin Sperl Changelog: V1 -> V2: applied feedback by Stefan Wahren reorganized patchset added extra rational, descriptions Signed-off-by: Mark Brown --- drivers/spi/spi-bcm2835.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-) (limited to 'drivers/spi/spi-bcm2835.c') diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c index 6c73e694794a..b7bb07c9507d 100644 --- a/drivers/spi/spi-bcm2835.c +++ b/drivers/spi/spi-bcm2835.c @@ -749,7 +749,6 @@ static int bcm2835_spi_transfer_one(struct spi_master *master, struct bcm2835_spi *bs = spi_master_get_devdata(master); unsigned long spi_hz, clk_hz, cdiv; unsigned long spi_used_hz; - unsigned long long xfer_time_us; u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS); /* set clock */ @@ -790,14 +789,15 @@ static int bcm2835_spi_transfer_one(struct spi_master *master, bs->tx_len = tfr->len; bs->rx_len = tfr->len; - /* calculate the estimated time in us the transfer runs */ - xfer_time_us = (unsigned long long)tfr->len - * 9 /* clocks/byte - SPI-HW waits 1 clock after each byte */ - * 1000000; - do_div(xfer_time_us, spi_used_hz); - - /* for short requests run polling*/ - if (xfer_time_us <= BCM2835_SPI_POLLING_LIMIT_US) + /* 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. + */ +#define HZ_PER_BYTE ((9 * 1000000) / BCM2835_SPI_POLLING_LIMIT_US) + /* run in polling mode for short transfers */ + if (tfr->len < spi_used_hz / HZ_PER_BYTE) return bcm2835_spi_transfer_one_poll(master, spi, tfr, cs); /* run in dma mode if conditions are right */ -- cgit v1.2.3