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spi: bcm2835: Avoid 64-bit arithmetic in xfer len calc

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Avoid 64 bit aritmetics when deciding if we need to use polling or not
This replicates: commit d704afffe6
("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>
This commit is contained in:
Martin Sperl 2019-04-23 20:15:09 +00:00 committed by Mark Brown
parent 9ac3f90db4
commit 7f1922eb3a
No known key found for this signature in database
GPG Key ID: 24D68B725D5487D0
1 changed files with 9 additions and 9 deletions
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18
drivers/spi/spi-bcm2835.c
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@ -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 */