Unverified Commit 7f1922eb authored by Martin Sperl's avatar Martin Sperl Committed by Mark Brown
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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 d704afff
("spi: bcm2835aux: Avoid 64-bit arithmetic in xfer len calc")
from spi-bcm2835aux

Signed-off-by: default avatarMartin Sperl <kernel@martin.sperl.org>

Changelog:
  V1 -> V2: applied feedback by Stefan Wahren
            reorganized patchset
	    added extra rational, descriptions
Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent 9ac3f90d

drivers/spi/spi-bcm2835.c

+9 −9
Original line number Diff line number Diff line
@@ -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 */

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