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>
diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c
index 6c73e69..b7bb07c 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 */
