On Wed, 2018-02-07 at 10:00 -0600, Gustavo A. R. Silva wrote: > Add suffix ULL to constant 9 in order to give the compiler complete > information about the proper arithmetic to use. Notice that this > constant is used in a context that expects an expression of type > unsigned long long (64 bits, unsigned). > > The expression tfr->len * 9 * 1000000 is currently being evaluated > using 32-bit arithmetic. > > Addresses-Coverity-ID: 1339619 > Signed-off-by: Gustavo A. R. Silva <gust...@embeddedor.com> > --- > drivers/spi/spi-bcm2835aux.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/spi/spi-bcm2835aux.c b/drivers/spi/spi-bcm2835aux.c > index 7428091..a768c23 100644 > --- a/drivers/spi/spi-bcm2835aux.c > +++ b/drivers/spi/spi-bcm2835aux.c > @@ -363,7 +363,7 @@ static int bcm2835aux_spi_transfer_one(struct spi_master > *master, > * chunk getting transferred - in our case the chunk size > * is 3 bytes, so we approximate this by 9 bits/byte > */ > - xfer_time_us = tfr->len * 9 * 1000000; > + xfer_time_us = tfr->len * 9ULL * 1000000; > do_div(xfer_time_us, spi_used_hz); > > /* run in polling mode for short transfers */ if (xfer_time_us < BCM2835_AUX_SPI_POLLING_LIMIT_US)
If one looks at the logic as a whole... tfr->len * 9ULL * 100000 / spi_used_hz < 30 A little algebra can change that into: tfr->len < spi_used_hz / 300000 So rather than add more 64-bit math, it can be removed entirely. Both the length and speed are 32 bits and there's no need to multiply them into something larger than might need 64 bits.