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| author | Martin Sperl <kernel@martin.sperl.org> | 2019-04-23 22:15:09 +0200 |
|---|---|---|
| committer | Mark Brown <broonie@kernel.org> | 2019-05-08 10:58:28 +0200 |
| commit | 7f1922eb3adba8c372fdf0d04fe9e6268f98291a (patch) | |
| tree | 0c3b4c5c706a4dbbee3eeda293d936879c2f642b /drivers/spi | |
| parent | spi: bcm2835: bcm2835_spi_transfer_one_poll remove unnecessary argument (diff) | |
| download | linux-7f1922eb3adba8c372fdf0d04fe9e6268f98291a.tar.xz linux-7f1922eb3adba8c372fdf0d04fe9e6268f98291a.zip | |
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 <kernel@martin.sperl.org>
Changelog:
V1 -> V2: applied feedback by Stefan Wahren
reorganized patchset
added extra rational, descriptions
Signed-off-by: Mark Brown <broonie@kernel.org>
Diffstat (limited to 'drivers/spi')
| -rw-r--r-- | drivers/spi/spi-bcm2835.c | 18 |
1 files changed, 9 insertions, 9 deletions
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 */ |