diff options
Diffstat (limited to 'drivers/spi')
| -rw-r--r-- | drivers/spi/spi-bcm2835aux.c | 18 |
1 files changed, 9 insertions, 9 deletions
diff --git a/drivers/spi/spi-bcm2835aux.c b/drivers/spi/spi-bcm2835aux.c index 7428091d3f5b..1431cb98fe40 100644 --- a/drivers/spi/spi-bcm2835aux.c +++ b/drivers/spi/spi-bcm2835aux.c @@ -321,7 +321,6 @@ static int bcm2835aux_spi_transfer_one(struct spi_master *master, struct bcm2835aux_spi *bs = spi_master_get_devdata(master); unsigned long spi_hz, clk_hz, speed; unsigned long spi_used_hz; - unsigned long long xfer_time_us; /* calculate the registers to handle * @@ -358,20 +357,21 @@ static int bcm2835aux_spi_transfer_one(struct spi_master *master, bs->rx_len = tfr->len; bs->pending = 0; - /* calculate the estimated time in us the transfer runs - * note that there are are 2 idle clocks after each - * chunk getting transferred - in our case the chunk size - * is 3 bytes, so we approximate this by 9 bits/byte + /* Calculate the estimated time in us the transfer runs. Note that + * there are are 2 idle clocks cycles after each chunk getting + * transferred - in our case the chunk size is 3 bytes, so we + * approximate this by 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 µs per 300,000 Hz of bus clock. */ - xfer_time_us = tfr->len * 9 * 1000000; - do_div(xfer_time_us, spi_used_hz); - +#define HZ_PER_BYTE ((9 * 1000000) / BCM2835_AUX_SPI_POLLING_LIMIT_US) /* run in polling mode for short transfers */ - if (xfer_time_us < BCM2835_AUX_SPI_POLLING_LIMIT_US) + if (tfr->len < spi_used_hz / HZ_PER_BYTE) return bcm2835aux_spi_transfer_one_poll(master, spi, tfr); /* run in interrupt mode for all others */ return bcm2835aux_spi_transfer_one_irq(master, spi, tfr); +#undef HZ_PER_BYTE } static int bcm2835aux_spi_prepare_message(struct spi_master *master, |